Polar Warming Spawns More Severe Winter Storms

So there’s a lot of groundbreaking work going on in the climate sciences right now. And a major focus is evidence that winter polar warming events are increasingly connected to blizzards and storms in places like Europe and North America. Storms that are both historically powerful and that occur with greater frequency.

(A historic nor’easter produces major flooding on the U.S. East Coast even as a blizzard pounds the UK in early March. Were these extreme storms linked to human-caused climate change and related rapid polar warming? A new scientific study says — yes. Image source: NASA Worldview.)

A new study led by pioneers in the emerging field of climate change attribution for extreme weather events (including the notable Dr. Jennifer Francis), finds:

Recent boreal winters have exhibited a large-scale seesaw temperature pattern characterized by an unusually warm Arctic and cold continents… Using a recently developed index of severe winter weather, we show that the occurrence of severe winter weather in the United States is significantly related to anomalies in pan-Arctic geopotential heights and temperatures.

In particular, the authors discovered thatwinter storms were two to four times more likely when the Arctic is abnormally warm, compared to when it was abnormally cold (emphasis added).”

Stronger, More Frequent Storms

This is a rather big deal for a number of reasons. First, it’s an observational confirmation of earlier scientific work predicting just these kinds of extreme weather instances due to polar warming and related climate change. Second, it’s another indicator that human-caused climate change is pushing us into a period of much stormier weather for the North Atlantic region during fall and winter.

(A new study in the journal Nature finds that winter storms in the U.S. are two to four times more likely when the Arctic is abnormally warm than when it is abnormally cold. Due to human-caused climate change, the Arctic is now warming up at a rate two times faster than the rest of the globe (emphasis added). Image source: Atmospheric and Environmental Research.)

With the new NASA global temperature data set out, I thought we’d take this opportunity to apply a bit of context to apparent stormy changes we see at present in winter weather patterns.

The first bit that I’d like to be crystal clear about is that the Arctic, overall, has become much, much warmer than usual during winter. That this warming spike occurs in the context overall global warming. And that this polar warming is increasingly associated with severe weather events in the middle latitudes and especially over the land and North Atlantic mid latitude zones.

The above graph shows polar temperature anomalies from the surface (1000 mb/2 meter) of the Earth to the top regions of the atmosphere (10 mb/25 kilometers). Along the bottom of the graph, we have a list of extreme weather events. Analyzing the graph we find that major polar warming associated with extreme temperature increases at the bottom of the atmosphere all the way through to the stratosphere correlate with recently more frequent historic blizzards and nor’easters in the regions mentioned.

Polar Warming Flushing Cooler Air into the Middle Latitudes

In previous posts, I used the ground-breaking scientific research of Dr. Jennifer Francis and others as a basis to analyze how energy transfer into the polar zone in the form of heat build-up has generated these extraordinary temperature extremes. How this ramping heat is associated with polar amplification — an aspect of human-caused climate change. And how these warming events can have upstream (Jet Stream) impacts that increase storminess in the middle latitudes.

(From January [top] to February [bottom] the pole heats up and extreme weather events ensue. Image source: NASA.)

But let’s take this analysis a step further to look at, as January progressed into February, where it got warmer, where it got colder, and where the big storms fired off.

The maps above show global temperature anomalies (NASA) for January (top) and February (bottom). And looking at those maps we find that the polar region heated up significantly from already warm ranges of 4 to 6.9 degrees Celsius above average during January to an amazing 4 to 12.3 C above average during February.

As this relative polar warming increased during February, the NASA maps show that colder than normal temperatures expanded over North America through Canada and parts of the Northern U.S. even as a cold spell began to blossom in Europe. Cold pools that were fed by Arctic air shunting southward as the Polar Vortex collapsed and remnant continental troughs emerged.

NASA’s zonal anomaly measures provide further evidence for this trend.

(Major northern polar warming from January [top] to February [bottom] is clearly visible in NASA’s zonal anomalies maps. Note that despite cold air excursions into North America and Europe, most zonal regions are warmer to much warmer than average.)

For here we find that as temperatures spiked from 4.5 degrees Celsius above average in the polar region of 80 to 90 degrees north latitude during January to an amazing 11 degrees above average during February, the region of 45 to 70 N dipped from 1 to 3 C warmer than average to 0.8 to 2.5 C warmer than average.

Note that the zonal middle latitude continental cooling is moderated by both the relatively warmer oceans and by very strong ridge zones running through these regions. But that the trough regions over both Europe and North America produced locally frigid temperatures and related instances of extreme weather.

Putting all these maps together from top to bottom we find that the polar warming events coincided both with mid latitude cooling even as we saw extreme snowfall in Canada and Montana, historic cold and snowfall in Europe and the UK, record flooding in the Central U.S., and record heat along the U.S. East Coast. We also find that the developing deep trough over Canada due to the expulsion of polar air southward in turn produced the succession of instabilities that would later spawn 3 very severe nor’easters off the U.S. East Coast during March.

Of course, all of these severe weather events are happening in the context of months that are around 1 degree Celsius warmer than 1880s averages globally. That January was the fifth hottest on record and that February was the sixth hottest on record during a La Nina that, all things being equal, should cause the world to be cooler than average.

But as we can see clearly here, all things are not equal — human-caused climate change is a big spoiler.


Sudden Stratospheric Warming and Polar Amplification: How Climate Change Interacts With the Polar Vortex

Over the past few years, the term Polar Vortex has dominated the broadcast weather media — gaining recent notoriety due to increasingly extreme weather events associated with a number of disruptions to Arctic atmospheric circulation patterns. In short, this swirl of cold air over the furthest north regions is being intensely disrupted by warm air invasions — both at the surface and in the upper levels of the atmosphere. A subject that we’ll explore further as part of this analysis.

Take the recent extreme February warming at the North Pole in which temperatures there rose to above freezing even as a major cold snap slammed into Europe this week. We’ve seen such varied headlines as Yes the North Pole is Warmer than Europe Right Now and Arctic Warm Event Stuns Scientists.

When it’s warmer at the pole than in Europe, it’s a sign that the weather is clearly out of whack. Especially when temperatures in a region spanning tens of thousands of square miles over the Arctic rocket to between 40 and 63 degrees Fahrenheit above normal. Scientists are notably concerned. Dr. Michael Mann, one of the world’s foremost experts on climate change characterized the polar warming event as:

…an anomaly among anomalies. It is far enough outside the historical range that it is worrying — it is a suggestion that there are further surprises in store as we continue to poke the angry beast that is our climate.

But what’s driving all this? Dr. Mann gives us a bit of a hint by describing our climate as an angry beast that’s being poked.

(Polar Amplification writ large. The entire region of the Arctic above the 80 degree North Latitude line has been 8.64 degrees Celsius warmer than normal for all of 2018 thus far. This is an extraordinary departure for a region that plays a critical role in how the Earth’s climate system functions. Image source: DMI.)

Perhaps another way to say it is that it’s a warming atmosphere that’s prodding the Jet Stream to take a chunk out of the Polar Vortex.

How might this work?

First, surface warming in the Arctic caused by increased radiative forcing from rising greenhouse gas levels and by follow-on reductions of Arctic sea ice and snow result in less temperature difference between the Pole and the Equator. This surface warming translates into higher levels of the atmosphere through convection.

Temperature difference is what drives the upper level winds. So a lower difference in temperature causes these winds to slow. When the Jet Stream winds slow, they tend to meander — forming large ridges and deep troughs. The elongated ridges and troughs eventually break like waves — pushing against the circulation of the Polar Vortex.

(NOAA graphic shows how a weak jet stream results in changes in atmospheric circulation and increased disruption of the Polar Vortex.)

When this happens, the speed of the winds that make up the Polar Vortex slow down and sometimes reverse. This results in the collapse of the column of upper level air held aloft by the Vortex’s winds. When the air collapses, it compresses, causing the stratosphere to warm. This falling column of warm air then can end up acting like an atmospheric wedge — driving the Polar Vortex apart and causing it to split.

The split then tends to generate smaller funnels that capture polar air and pull it south. Beneath the funnels, it can be quite cold as Arctic air invades places like North America or the UK (as happened this week). But at the Pole, where the cold air should typically reside, it warms up enormously.

That’s how, under a regime of human-forced climate change, you can end up with periods where temperatures are warmer at the Pole than they are in Europe.

It’s worth noting that Polar Vortex collapse events did occur in the past. But not in such a way that generated the kinds of historically extreme Arctic temperatures we see today. The primary driver for the recently increased extremity of weather driven by Polar Vortex collapse events being human-caused climate change, Polar Amplification, and related influences on the Jet Stream.

NOAA’s 2016 Report Card: The Arctic is Shouting Change

From winter to spring to summer to fall, it’s been an odd year for the Arctic. And according to Donald Perovich, one of the authors of NOAA’s 2016 Arctic Report Card, the Arctic isn’t just whispering change, it’s not foretelling change, “it’s shouting change.

(NOAA’s Arctic Report Card presented at the American Geophysical Union this morning. Video source: AGU.)


Winter and spring of 2016 saw very warm temperatures in the northern polar region of our world. There, Arctic sea ice extent maximum hit its lowest values ever recorded in March. During summer, cooler, cloudier conditions prevented a complete meltdown by the time of sea ice minimum in September. However, sea ice extent bottomed out at second or third lowest on record in most of the major monitors. Moving into October, November and December, Arctic sea ice failed to refreeze at typical rates as extraordinarily warm temperatures were reinforced by pulses of air rising northward from the middle latitudes. At times, the gap between previous record low years and the new record lows seen during November of 2016 were as much as 1.1 million square kilometers. Now it is practically certain that average sea ice extents throughout 2016 will hit a new record low overall.

Arctic Warming at Least Twice as Fast as Rest of World

Much of this melt was almost certainly driven by the record warm Arctic temperatures seen during 2016. And according to NOAA, this year shattered all previous high marks for Arctic heat by a big margin — hitting 3.5 degrees Celsius warmer than 1900. Overall, this rate of warming is at least twice as fast as the rest of the globe.


(Arctic heat during 2016 centered over recently seasonal and annual ice free regions in the Chukchi and Barents seas. It’s an indicator that sea ice loss since 2007 and related loss of albedo [reflectivity] is starting to have the predicted heat-amplifying effect. Image source: NOAA.)

And all this extra heat has not only had a significant and substantial impact on sea ice — it is hammering the Greenland ice sheet, forcing the permafrost to rapidly thaw, and increasing the incidence of algae blooms related to ocean acidification.

Greenland Melt and Permafrost Thaw

In Greenland, the average annual rate of land ice loss is now 230 billion tons per year. This despite the fact that warming in the Greenland and Barents seas is helping to drive increased rates of precipitation in Eastern Greenland. So far, much of the precipitation is coming as snowfall. And this increase is helping to mitigate some of the mass losses due to melt across Greenland (see Marco Tedesco’s comments in the video above). However, as Greenland continues to experience surface warming, precipitation is likely to come more and more as rain — which will only further help to accelerate melt.

NOAA also notes that added Arctic heat has substantially altered the permafrost. Increasingly, this region of frozen soil is given over to thaw. As a result, profound changes to the Arctic landscape are ongoing. In wet regions, the permafrost is giving way to thermokarst lakes. In drier zones, the moisture that was locked into the soil and preserved by permafrost is being steadily lost — which is one of the primary drivers of drought and related wildfire hazards now being experienced in Canada, Siberia, and Alaska.


(As permafrost thaws, microbes within the soil break down carbon and begin to emit methane and carbon dioxide. According to NOAA, “the warming tundra is now releasing more carbon into the atmosphere than it is taking up.” Image source: NOAA.)

Overall, the permafrost is emitting more and more methane and carbon dioxide as it melts and as microbes in the thawed soil activate. And consensus science now indicates that, on balance, this thawing ground is now emitting more carbon than it is taking in. This is a step change from its previous state — when the frozen land acted in concert with the boreal forests as one of the world’s primary carbon sinks (please also see: Beyond the Point of No Return).

Large Algae Blooms Indicator of Ocean Acidification

During 2016, the Arctic also saw a continuation of large algae blooms popping up in regions near the receding sea ice edge. This happens as high nutrient waters liberated by ice allow sunlight to produce a riot of plankton and algae growth. These minute life forms take in atmospheric carbon. But as they die, they transfer this carbon to the ocean. As a result, and as Jeremy Mathis noted in the press briefing this morning (see video above), Ocean acidification increases.

Conditions in Context — The Arctic Screams Change

The above indicators present a picture of an Arctic undergoing rapid climate destabilization. As a result, everything from weather patterns, to the rate of sea level rise, to Northern Hemisphere growing seasons are likely to see some impact from these Arctic changes over the coming years and decades. In addition, loss of sea ice and likely harms to life in the Arctic Ocean due to warming, habitat loss, and ocean acidification will remove food sources for local communities.

NOAA researchers identify some potential positive outcomes — such as increased commerce, ship traffic, tourism, and mineral extraction. But it is difficult to see how these supposed positives do not further exacerbate an already difficult to manage problem. Increased commerce, ship traffic and tourism threaten to harm already stressed habitats and animal populations. In addition, if new fossil fuel sources are exploited in the region, it will only add to the currently severe problems presented by warming. As a result, there is a high likelihood that the net impact to the region will be starkly negative as species are threatened or go extinct and numerous communities are lost to the rising seas, destruction of environmental resource bases or endangered by worsening fires.


AGU Fall Meeting

NOAA’s Arctic Report Card

Beyond the Point of No Return

Thermokarst Lakes

Hat tip to Vic


Denying The Neverending Heatwave: NASA, NOAA, JMA Show 2014 Broke New Records; But Will Republicans Ever Listen to Science?

If you are younger than 29 years old, you haven’t lived in a month that was cooler than the 20th century average. — Dr. Marshall Shepherd, former President of the American Meteorological Society

*   *   *   *   *

Strong global temperature records typically show up in all the major climate monitors. And, despite no El Nino providing an added kick to atmospheric heating, that’s exactly what happened in 2014.

Respectively Japan’s Meteorological Agency (JMA), NASA and NOAA all showed 2014 as the hottest year in the global climate record. And the departures were all quite strong with JMA showing +0.63 C, NASA showing +0.68 C, and NOAA showing +0.69 C above the 20th Century average — all measures that put the world now in the range of +0.9 C warming since the 1880s.

Not only was this year the hottest on record for the global climate. It was one in many progressively hotter years and decades. The result being that if you were born in 1986, you haven’t experienced one month that has been cooler than the 20th Century average.

Decadal and Yearly Warming NOAA

(Decadal and yearly warming since 1880 as recorded by the National Oceanic and Atmospheric Administration. It’s a brutal warming trend that has propelled us, in just 1 Century, into a time hotter than any in at least 5,000 years and probably 150,000 years. Continued warming at this pace will put us hotter than at any time in 1 million years before mid century and that is without any of the predicted acceleration due to amplifying feedbacks such as Arctic carbon release, loss of Arctic albedo due to snow and ice melt and greening, and loss of the oceans as a global carbon sink. Image source: NOAA and Climate Progress.)

It’s a set of validated evidence that is so obvious as to be incontrovertible.

And yet the climate games and silliness still occur with regularity in the public sphere. In the most recent republican witching hour congressional approval of the Keystone XL pipeline — a piece of infrastructure that will shackle the US to climate-wrecking carbon emissions for decades to come — Bernie Sanders submitted an amendment asking republicans to record their climate change denial for the public record. A denial a majority of republicans, including most major party heads, now attest to, despite what the science is obviously saying.

In an interview with the Guardian, Sanders noted:

“The bottom line is that I think as a nation that we walk down a very dangerous road when the majority party in the United States Congress is prepared to reject science. I think it is important for Republicans to tell their constituents, to tell the American people, and to tell the world whether they agree with the science or not.”

More notably, Senator Jim Inhofe, who currently sits as chairman of the environment and public works committee has publicly claimed that he believes climate change is a hoax. But what Inhofe doesn’t elaborate is why scientists who spend their lives in service to the public, and not to special interests, like the oil, gas and coal companies Inhofe often goes to bat for in Congress, would perpetrate such a hoax. Because if it is a hoax it is broad and all-encompassing — including every major atmospheric sciences body in the world today. In other words, if Inhofe believes NASA put a man on the moon, then why doesn’t he believe the same scientific body on the issue of climate change?

Climate Scientist Michael Mann gave his own very clear take of the new record today on Facebook. Mann noted that the current new record, especially when viewed in context of the fact that we currently see no El Nino but still hit annual heat records, can put to rest the recent false assertions that atmospheric warming has paused.

As ever, Mann provides a very clear assessment:

Based on the collective reports, it is therefore fair to declare 2014 the warmest year on record. This is significant for a number of reasons. Unlike past record years, 2014 broke the record without the “assist” of a large El Niño event. There was only the weakest semblance of an El Niño and tropical Pacific warmth contributed only moderately to the record 2014 global temperatures.

Viewed in context, the record temperatures underscore the undeniable fact that we are witnessing, before our eyes, the effects of human-caused climate change. It is exceptionally unlikely that we would be seeing a record year, during a record warm decade, during a multidecadal period of warmth that appears to be unrivaled over at least the past millennium, were it not for the rising levels of planet-warming gases produced by fossil fuel burning.

The record temperatures *should* put to rest the absurd notion of a “pause” (what I refer to as the “Faux Pause” in Scientific American: in global warming.

There is a solid body of research now showing that any apparent slow-down of warming during the past decade was likely due to natural short-term factors (like small changes in solar output and volcanic activity) and internal fluctuations related to e.g. the El Nino phenomenon. The record 2014 temperatures underscore the fact that global warming and associated climate changes continue unabated as we continue to raise the concentrations of greenhouse gases in the atmosphere.

Mann was joined by lead NASA GISS scientist Gavin Schmidt who pointed out the inexorable global warming of ‘decades and decades.’ Schmidt noted that individual years rankings can be slung about through the forces of chaotic weather. But the trend, Schmidt asserted, was undeniable.

Dr. Schmidt’s research has been critical in understanding the role of both CO2 as the primary governing gas impacting global heating as well as the amplifying heat of additional greenhouse gasses. In the late 1990s and early 2000s Dr. Schmidt provided critical evidence highlighting the atmospheric warming impact of methane, for example.

NASA and Dr Schmidt provide their own brief on the issue which can be viewed here:

Dr. Jennifer Francis of Rutgers, who is now engaged in cutting edge research on the issue of changes in the Jet Stream due to polar amplification, joins the litany of influential scientists in speaking out on the new record. Of the impact of the 2014 high heat mark she plainly states: “Any wisps of doubt that human activities are at fault are now gone with the wind.”

NOAA’s own global analysis this year comes with a near-endless list of record flood and drought events ongoing throughout 2014. I highly suggest you read the report. The language is dry, but the list of record events is staggering, even to someone like myself who is treated to these events on a daily basis. They’re exactly the kind of outlier events that are the upshot of meridional patterns, polar amplification, and the meandering Jet Streams identified by Dr. Francis. A list of extreme instances that propelled 2014 into another record-breaking year for natural disasters, according to Munich Re:

Natural Disater List Munich Re

(List of natural disasters in number of instances per year as reported by Munich Re. Image source: Climate Progress.)

The evidence is there. All of it. For any thinking person. The public-serving, and often conservative in their assessments, scientists keep making their warnings again and again like a collective modern Jeremiah. And yet we have one political party whose leaders simply refuse to listen to either facts or even the most basic reason.

So in the face of such blantant and obvious denial of reality by the very people who are supposed to be responsibly leading our country, one must seriously consider the notion of running them out of office. Of stopping their legislative malpractice before it results in ever more serious trouble for us all. And not just for all the sakes of the scientists and those who believe them, but for the sake of the climate change deniers too.

Drought, Burning Rings of Fire out West, Severe Flooding in the East: How Climate Change and a Mangled Jet Stream Wrecked US Weather

Earlier this summer, I had a weather conversation with my mother. She was excited about a new business venture my sister had undertaken (Adventure Kayaks) and for an upcoming trip to Yosemite in August to celebrate her and my father’s 45th wedding anniversary. She wondered about the weather, hoping it would be a good summer for both the new business and the trip. Without thinking too much, I said:

‘Rain, cooler weather, and storms in the east, drought, heat and fires in the west.’

Immediately after saying this, I felt reticent. Perhaps I shouldn’t have spoken? Maybe I would scare my mom. What good would it do to ruin her enjoyment or her looking forward to both the trip and to my sister’s potential success?

It’s worth noting that, thankfully, the storms and cooler weather that did emerge with fury and flood in the east did not ruin my sister’s kayaking venture (although it did result in numerous interruptions both during spring and throughout summer). Should a tropical storm or hurricane make landfall on the US east coast this August, September or October, however, the devastation could be vast, perhaps exceeding a 1 billion dollar disaster event (more on this below).

But as my mother boarded her plane to California and a potential date with Yosemite yesterday morning, these were the satellite images I was looking at:

Yosemite Fire NASA Earth Observatory

Yosemite Fire NASA Earth Observatory

Image source: Earth Observatory

The vast Rim fire that had grown to consume over 192,000 acres as of today was steadily devouring the western border of Yosemite. You can see it on the above infrared satellite picture provided by NASA as a ring of bright white steadily inching into the indicated yellow border of Yosemite.

Jennifer Francis, Stu Ostro and How I Knew

Earlier this summer, my mother chided me on my ‘attempts to predict the weather.’ In a phone conversation last night, she asked ‘how did you know?’

It’s fair to say that in the overall prediction of more storms and rains in the US east, with more risk of flooding, and more heat and dryness out west, with more risks of fire, that I wasn’t entirely certain. However, I’d recently read the work of climatologist Jennifer Francis and had been listening to and following the statements of Stu Ostro. During early spring and summer, I observed a Jet Stream pattern setting up over the US that appeared to be settling into a ‘stuck position’ that would result in the high likelihood of the conditions I communicated with my mother. It’s worth noting that in looking at these Jet Stream patterns it’s not difficult to make such predictions because the patterns change slowly, they lumber and tend to remain stuck for long periods. Once a pattern settles into place, it’s a good bet that it will stick around for at least a few months these days, a fact that the models nail but which meteorologists, in general, have failed to communicate. In short, this is a climate change driven change in the weather.

In fact, some meteorologists and climatologists seem entirely reticent to accept this new weather pattern, despite the fact that it is a powerful tool for weather prediction and will tend to result in less surprises. The big troughs equal record floods sticking around for a long time and the big ridges equal record heat, drought, and probably fires sticking around for long periods of time.

In an example of this reticence, a recent paper by a University of Colorado researcher concluded that Jennifer Francis did not have enough evidence to support her claims of an observed slowing in the Jet Stream. Unfortunately, the paper included, as a part of its findings, a cross section of the atmosphere in which the Jet Stream does not typically reside even while the paper included a sample during which changes were already occurring, which would have likely biased its results. Despite these biases and errors, where the paper actually did measure Jet Stream flows, it corroborated Francis, showing Jet Stream slowing during the periods measured. This is odd considering the fact that the concluding statement contradicts the papers own findings, a point which Dr. Francis, herself, provides.

It’s easy to understand why reticence still lives in the science. As I noted above, it’s understandable to feel reticent when being the bearer of bad news. No one wants to be the messenger that gets metaphorically ‘killed.’ But without making use of the clear understanding provided by Francis and Ostro, we will continue to be surprised by extreme floods, storms, fires, heatwaves and droughts that can be easily predicted by simply looking at how the Jet Stream sets up and where it gets stuck. Instead, ‘surprise’ after ‘surprise’ just keeps coming our way.

When Rossby Waves Get Stuck: Changing to a More Radical Jet Stream

Dr. Jennifer Francis has observed that loss of sea ice and snow cover in the Northern Hemisphere has resulted in a slowing of the Jet Stream in recent years. Sea ice volume, the measure of total ice in the Arctic Ocean, since 1979 had declined by as much as 80% when measured at its low during 2012 (this measure may rally back to around 75 to 78 percent lower than 1979 this year, but the overall trend remains a death spiral). Greenland melt is unprecedented at 500 gigatons per year and with Arctic heatwaves blasting the tundra both permafrost and snow cover are at record and near record lows. 80 to 90 degree temperatures now often advance to the shores of the Arctic Ocean, with the coldest air pushed back above the 80 degree north latitude line, confining it to a shrinking region that, increasingly, huddles closer to the remaining large ice sheets in Greenland. Overall rates of warming for much of the Arctic are about .5 degrees C temperature increase each decade, more than twice the global average.

A more quickly warming Arctic results in changes to the atmosphere’s heat balance. According to Francis, the height of the atmosphere over the Arctic is rising relative to atmospheric heights in the lower lattitudes, this loss of slope results in lower gradients from north to south and since temperature, atmospheric height and pressure gradient drive Jet Stream speed, the Jet Stream slows down. And as the Jet Stream slows, it tends to seek out the highest gradients it can find. The result is more northward invasions of the polar region of the Jet Stream ridges and more southward invasion of the Jet Stream troughs. This amplification creates a rather large and elongated sine wave called a Rossby wave pattern.

Jet Stream Pattern Change. Image source: NOAA.

Jet Stream Pattern Change. Image source: NOAA.

In the sequence above, we see the progression of a flat Jet Stream to a Rossby wave ridge/trough configuration to, eventually, cut off lows and highs. In the past, such waves tended to set up for briefer periods, extending for days or weeks before returning to the usual, more flattened motion of the Jet. In more recent years, large Rossby type waves have been the typical pattern, one that transitions to cut off lows before it returns to a configuration more similar to (b) in the diagram, before setting up as a Rossby-type wave again.

Perhaps more importantly, this b, c, d progression has tended to occur again and again and again over the same geographical region for months and months on end. And, looking back at Jet Stream maps over the past months, this is exactly what we find.

Below is a progression of images I’m providing from this blog’s archive. It includes either direct temperature measures that indicate Jet Stream patterns or a mapping of air flow speed indicating the Jet Stream’s path.

Clover leaf Jet Stream Pattern April, 2013.

Clover leaf Jet Stream Pattern April, 2013.

(Image source: ECMWF)

In ‘For Central US, Climate Change and a Mangled Jet Stream Means Drought Follows Flood Follows Drought’ I described how the Jet Stream pattern had consistently switched from large trough to large ridge configurations over the past few years bringing either heatwaves and droughts or storms and floods. But the left hand portion of the image provides a good record of the Jet Stream configuration as of mid April this year. Following the temperatures, on the west coast we see a large, hot ridge and in the central and eastern US we see a deep, cool and stormy trough.

Wednesday July 3, Rossby wave still in effect over US.

Wednesday July 3, Rossby wave still in effect over US.

(Image source: ECMWF)

Throughout May and into June, this ridge over west, trough over east, pattern continued. By late June, a massive, record-shattering heatwave had set up over the US southwest. I described this highly anomalous event in ‘Mangled Jet Stream and Global Warming to Shatter Earth’s Highest Recorded Temperature This Week?’

Looking at the ECMWF image above we again see the highly exaggerated ridge/trough dichotomy setting up over the US with very hot, dry conditions out west and cooler, wet and stormy conditions in the east.

At this point, I want to tap Stu Ostro’s own observations to add to the Jennifer Francis mix. What Stu has found is that large, powerful high pressure systems have tended to develop more and more often. These extraordinarily dense systems seem to be exploding to new heights in a thickening atmosphere. Primarily, these monsters are driven by heat and so they tend to live in the massive ridges provided by our new, exaggerated and slowed, Jet Stream pattern. That said, these beasts can spring up almost anywhere there is a massive abundance of heat to tap, as one did over a super-heated region of ocean near Shanghai this summer sparking its own monstrous heat wave.

These large heat domes have major and far reaching effects. To understand them, we must first step back to think about the broader effects of human caused warming before looking at how heat domes manifest in the atmosphere. Based on models of the Earth’s atmosphere, we know that for each 1 degree Celsius of Earth temperature increase we get a corresponding 8% amplification of the hydrological cycle. What this means is that evaporation happens 8% faster and condensation happens 8% faster — OVERALL.

Since 1998, we have observed temperatures that are, on average, .8 degrees Celsius above those seen during the 1880s. What this means is that the hydrological cycle has amplified by 6% over this same time period. Because of this dynamic, droughts are more intense, but rainfall events are also more intense. Yet since the atmosphere is uneven we can expect this 6% amplification to manifest in somewhat more extreme fashion at the locations where more extreme Jet Stream patterns set up.

Mangled Jet Stream Dumps Deluge on US Midwest

Mangled Jet Stream Dumps Deluge on US Midwest

(Image source: California Regional Weather Server)

What goes up must come down. And that massive heat dome over the western US and Canada had been baking moisture out of the soil at unprecedented rates over an extended period from April to August. The moisture injected into the heat dome rose and rose, The high pressure system suppressed cloud formation so the moisture had no where to go but up and out. Eventually, this moisture found the edge of the massive high and spilled over into the storms riding along the Jet Stream trough rushing down from the Arctic Ocean and into eastern Canada and the US (hat tip to Colorado Bob).

The result was multiple flood events starting with the Midwest floods of April, then the massive Canadian floods (Calgary) of June, then the Toronto floods, then the Midwest floods of early August, and lastly the east coast floods of mid to late August. The Calgary floods were the worst ever recorded in Canada, the Toronto floods were the worst recorded for that region, and in the Midwest floods of early August, four months worth of rain fell in just one week.

Monthly rainfall estimates August 2013.

Monthly rainfall estimates August 2013.

(Image source: The Weather Channel)

On 8 August, the time of the second barrage of major Midwest floods this year, we find the Jet Stream in the same elongated configuration with a large northward ridge extending all the way from the southwestern US to the Arctic Ocean and with a deep trough diving back down into the central and eastern United States. As noted above, the mangled Jet Stream delivered its overburden of moisture directly to the US Midwest, dumping four months worth of rain in just one week.

A second pulse of moisture rode far south along this Jet Stream flow to dump massive amounts of rain over the southeastern US about a week after pummeling Missouri. This flow combined with a compromised tropical system to saturate the southeast, with some regions receiving as much as 300 percent their annual rainfall totals by late August.

One of the hardest hit areas is Lake Okeechobee. Water levels there as of mid August hit 16 feet at the Hoover Dike, a level that requires weekly monitoring for cracks or ruptures. The dike stretches over 140 miles along the perimeter of lake Okeechobee and was intended to keep the lake in check during major storms and hurricanes after large outburst events in the early 20th Century resulted in thousands of lives lost. The dike is 25 to 30 feet high and is as wide as a football field. The US Army Corps of Engineers has been working feverishly to shore up the dike in a project that will take years to complete.

At 16.5 feet water level, the dike will require daily monitoring. For each inch of increase above that level, the pressure put on the dike would greatly increase risks of catastrophic failure. The causes of such high water, this year, were neither tropical storms nor hurricanes. Florida has been, thus far, spared the wrath of these strong storms. Deep Jet Stream troughs and a constant Atlantic moisture flow have, instead, resulted in day after day rain events for much of southern Florida, pushing August totals near Lake Okeechobee above 16 inches, filling the massive lake and putting the dikes at risk. Should a hurricane or tropical storm strike Florida during late August, September, or October, the dike could overtop or rupture, unleashing the massive lake on communities sitting beneath it. (Hat tip to Colorado Bob).

As the threat of massive floods continued to increase in the east, the west was erupting with wildfires. Fire containment efforts went into high gear both exhausting the Forest Service Fire budget and briefly pushing the national fire alert level to 5. The Rim Fire, so close to my parents’ vacation site, expanded to 192,723 acres today making it the 6th worst in California history.

Rim Fire on August 28th, 2013

s Rim Fire on August 28th, 2013

(Image source: Lance-Modis)

You can see this massive fire, now 23% contained, burning to the west of Yosemite in the Modis shot below. A more detailed report of this major wildfire is provided by WeatherUnderground here and here.

Mangled Jet Stream Temporarily Edges Eastward

My parents wanted to see Yosemite’s amazing waterfalls. A major source of my reticence in telling them the likely pattern for this summer was that the heat and drought out west would probably dry out many of those magnificent falls. And, sadly, this has happened. So even if they brave the smoke and fires to reach Yosemite, the one attraction my mom had been most excited to see will likely be somewhat less magnificent.

But a cloud has suddenly appeared in this wrinkle. For the Jet Stream had edged slightly east.

As of the middle of last week, reports of heatwave conditions had emerged throughout the US Midwest with North Dakota, South Dakota, Nebraska, Illinois, Wisconsin, Iowa, Minnesota and Missouri experiencing temperatures in the range of 20 degrees (Fahrenheit) above average. With heat index values hitting as high as 110 degrees, communities sweltered and school systems declared closings. In California, where temperatures had remained in the upper 90s to lower 100s for much of summer, the trough advanced, pushing temperatures back down to the 70s. An upper level low flirting with the west coast may even toss a few fog clouds and rain showers toward California. Such an event would be a welcome change for both my parents and for beleaguered fire fighters in the region.

In any case, the shift is expected to be short lived with ECMWF models showing the Jet Stream again backing up and reforming a hot and dry ridge pattern over the US west. So the Midwest can expect cooling and a return to more stormy, rainy conditions while the US west, after only a brief respite, continues to bake:

Mangled Jet Stream Early September

(Image source: ECMWF)

The September 7 ECMWF forecast again shows a large and powerful Rossby-type wave pattern with a very large and hot ridge setting up over the US and Canadian West with a deep trough digging down toward the US East Coast. It is the same pattern we’ve seen since at least April, a pattern that has delivered numerous rounds of heat and drought to the US west and an equally vicious and persistent pattern of storms and flooding from the central US to the east coast. The Jet Stream has, essentially, been stuck these past 5 months and there is no end in sight. For even if this configuration of the Jet were to move, it would likely simply re-distribute the locations of heatwaves and droughts and storms and floods.

If anything, this past summer has been yet one more validation in evidence of the work of Dr. Francis. And it is because of her work that I, a relatively untrained observer, can make the accurate prediction that a large region from the Mississippi west to California will continue to stay hot and dry and will continue to see risk for large fires, while the region to the east will remain cooler and stormier so long as the current Jet Stream configuration continues to persist. The western region will risk periods of record heat, continued drying of lands, rivers and aquifers, and fires of record size. The eastern region will continue to risk record floods and storm events. As summer proceeds to fall, shifts in these weather patterns have the potential to grow violent with the possibility of powerful nor-easters or hybrid storms developing near the US East Coast. Both the southeast and Florida remain very vulnerable to continued large rain events or tropical storms and hurricanes as time moves forward and in the event of pattern persistence. Meanwhile, long range model forecasts show this general pattern continuing to persist until at least early to mid September.

At this point, the current US Jet Stream pattern will have been in place for at least 6 months.




Why Global Warming Should Keep You Awake at Night: Dr. Jennifer Francis Gives Chilling Testimony to Congress


In a July 18 testimony to Congress, Dr. Jennifer Francis, an atmospheric scientist from Rutgers and key innovator to understanding how climate change has brought about dangerous alterations to the Northern Hemisphere Jet Stream, provides five compelling reasons why we should all be quite concerned about human caused global warming.

They include:

1. CO2 levels are higher than they’ve been in probably 2.5 million years.

2. The northern polar sea ice has lost more than 3/4 (80% ) of its volume since 1979.

3. The pace of sea level rise is accelerating.

4. The Arctic has warmed 2-3 times faster than the rest of the Northern Hemisphere.

5. Climate misleaders deliberately ignore and misconstrue the science.

The video is well worth the five minutes it takes to watch. A more in depth PDF was also provided for those looking to dig deeper.

Hat tip to Peter Sinclair for the heads up.

Double Barrel Retrograde Low Sets Off Rain, Flooding From East Coast to Desert Southwest

Double Barrel Retrograde

(Image source: NOAA)

An upper level low that originated this  weekend west of the Appalachians has now transitioned all the way to the New Mexico, Arizona border. If it continues this motion, it will exit the continent somewhere near Baja or Southern California this weekend, having pushed over 3,000 miles against an extraordinarily week Jet Stream.

Yesterday, a second low developed in the wake of the first over the southeast, slowly drifting east to west behind the first.

Today, this double barrel retrograde system brought rains and localized flooding to a wide region including Florida, Georgia, the Carolinas, Texas, New Mexico and Arizona. Miami, which consistently suffers from flooding these days due to an antiquated water management system unable to cope with encroaching seas and more intense rains brought on by climate change, was blanketed by high waters. City offices handed out sandbags to residents who saw roadways, golf courses and yards disappear beneath the flooding rains.

In Atlanta, warnings were issued as a local river approached flood stage and waters continued to rapidly rise as  Houston experienced flooded roads and dangerous driving conditions. Less heavy downpours were reported throughout the Carolinas and into New Mexico and Arizona. The western rains may be welcome, as they help to alleviate drought conditions that have lasted for more than a year. In the east, rainfall has saturated many areas causing added concern for what is expected to be a busy hurricane season.

This rainy, backwards moving weather has been facilitated by an extraordinary weakness in the Jet Stream over the US. The pattern and weak upper level wind flow have resulted in retrograde weather affecting much of the US, now for five days running. You can view these dual weather systems moving backward over the US via the following NOAA animation:

The first retrograde low can be seen moving into Arizona, the second is centered over Georgia, and another system looping over Maine and into the backward upper level wind pattern will potentially recurve into the East Coast over the next 36 hours.

Dr. Jennifer Francis of Rutgers University has been presenting compelling research that shows that Arctic sea ice loss significantly affects the upper-level atmospheric circulation, slowing its winds and increasing its tendency to make contorted high-amplitude loops. Such high-amplitude loops in the upper level wind pattern (and associated jet stream) increase the probability of persistent (that is, longer-duration) weather patterns in the Northern Hemisphere, potentially leading to extreme weather due to longer-duration cold spells, snow events, heat waves, flooding events, and drought conditions.

Given the strange backward moving weather events of the past week, weather system motion retrograde to typical upper level flows may also be a likely result.



Jet Stream so Weak, Weather is Moving Backwards

Greenland Melt Exceeds Summer Maximum in Early June. “Storms of My Grandchildren” on the Horizon?


(Image source: NSIDC)

According to reports from NSIDC, Greenland ice sheet melt had exceeded average summer maximum values by Tuesday, June 11th, about a month and a half earlier than normal.

On Tuesday, about 24% of the Greenland ice sheet had experienced melting. This value is about 1% higher than the usual summer maximum of 23% melt coverage.

2013’s early, widespread melt follows just one year after melt covered nearly all the Greenland ice sheet for days during July of 2012. 2012’s melt was the strongest for Greenland in at least 120 years. For 2013 melt values to approach or meet 2012 melt values would further reinforce a powerful increase in Greenland melt that has occurred since the 1990s. Since that time, the rate of Greenland melt has more than tripled.

June 2013 has established a trend of rapidly increasing melt that sets in place conditions for past record values to potentially be challenged. As such, it is well worth monitoring conditions as they develop.


(Visual of Greenland melt coverage on June 12th. Image source: NSIDC)

Scientists now are at odds over how fast Greenland melt will increase. Some believe a linear increase in melt is most likely while others believe that exponential increases in Greenland ice sheet melt are not out of the question. Should the increasing pace of melt for Greenland continue, powerful changes in the weather, especially for Europe and North America are in store. This winter and spring’s extreme weather over much of Europe may just be a foretaste of what is to come.

Storms of My Grandchildren on the Horizon

Massive melt from Greenland by or before mid-century means large volumes of fresh water in the North Atlantic. These high volumes of fresh water could substantially slow or even halt the Gulf Stream. Present measures of Gulf Stream circulation already show the current slowing. If these trends continue, the replacement of this warm water stream with cold water from Greenland will radically alter northern hemisphere weather.

The Weather Channel provided a brief summary of some of the possible impacts of slowing Gulf Stream currents here.

Even worse, under human caused climate change, a cooling of the North Atlantic occurs at about the same time tropical and temperate region temperatures begin to rapidly rise. This creates a high gradient between cold air near Greenland and warm air directly to the south. The result, according to models, is powerful storms never seen before in human memory.

In “The Storms of My Grandchildren,” NASA scientist James Hansen warned of the potential for frontal storms large enough to span continents and packing the punch of hurricanes. Is is just these kinds of storms that rapid Greenland melt combined with intensified warming at the tropics could set off.

The conditions for these events appears to be ramping up now and could be present, in the worst case, by as soon as the 2030s. In the meantime, weather conditions are likely to continue to deteriorate as a combination of sea ice melt and Greenland ice sheet melt play havoc with traditional weather patterns.

Alterations to the Northern Hemisphere Jet Stream as demonstrated by the work of Dr. Jennifer Francis is one such change that is already present. And this alteration has already resulted in several instances of enhanced severe weather.

Meanwhile, in more southerly regions, we find that the seasons for tropical storm development are lengthening. Dr. Jeff Masters of WeatherUnderground made the following statement in reference to the early June formation of Tropical Storm Andrea:

Andrea’s formation in June continues a pattern of an unusually large number of early-season Atlantic named storms we’ve seen in recent years. Climatologically, June is the second quietest month of the Atlantic hurricane season, behind November. During the period 1870 – 2012, we averaged one named storm every two years in June, and 0.7 named storms per year during May and June. In the nineteen years since the current active hurricane period began in 1995, there have been fifteen June named storms (if we include 2013′s Tropical Storm Andrea.) June activity has nearly doubled since 1995, and May activity has more than doubled (there were seventeen May storms in the 75-year period 1870 – 1994, compared to 6 in the 19-year period 1995 – 2013.) Some of this difference can be attributed to observation gaps, due to the lack of satellite data before 1966.

So storminess increases at the tropics and storminess increases at the poles. When these two conditions meet, the potential exists for amazingly powerful and freakish storms similar to, but even worse, than Hurricane Sandy. It is the potential of global warming to set in place conditions where powerful storms can combine, persist, and expand over vast areas that is a threat we must consider as Greenland melt continues to increase, Arctic sea ice melt progresses, and warming in the tropics and temperate zones continues to expand.



The Weather Channel Observes Slowing Gulf Stream

The Storms of My Grandchildren


Masters: Hurricane Season Getting Longer

The Greenland High, Blocking Patterns and Sandy’s Arctic Arm: How Climate Scientists, Journalists and Bloggers Warned Of New Potential For Extreme Storms Before Sandy

Over the coming weeks, you will hear any number of people trying to ‘normalize’ the unprecedented weather event that was Sandy. You will hear people trying to over-emphasize Sandy’s link to ‘natural climate variability.’ You will hear people claiming that extreme events like Sandy could have never been predicted. And you will hear people trying to take Sandy out of a context in which the US has just experienced its hottest year on record, is still experiencing one of its worst droughts on record, has just experienced its most extreme climate year ever, and during a year in which Arctic Sea Ice has melted to extreme record lows.

And you should be assured — people taking Sandy out of a context of an ongoing string of extreme climate impacts as well as making these other assertions are entirely and completely wrong. Further, it is important to note that we were warned about the increased possibility of extreme storms like Sandy in the weeks and months before Sandy formed.

(Looking at this GOES satellite picture, you can see the swirl of clouds that is Sandy just off the South Carolina coast. See that long arm of clouds stretching down from the Arctic and then feeding into Sandy? That’s Sandy’s Arctic Arm.)

A key ingredient that made Sandy so intense was not just the 5 degree Fahrenheit above average temperatures in the Atlantic Ocean off the East Coast. This five degree warming was fed by an increase of 1  degrees of average Ocean temperature warming over the past century, pushing the potential for extreme years higher. An overall warming directly fueled by human carbon emissions. These increased temperatures and related increases in water vapor fueled Sandy, making her larger and stronger. These were clear global warming impacts that enhanced Sandy’s size and strength. But the kicker, the added boost that made Sandy a monster storm, the influence that pulled Sandy into the East Coast at such a destructive angle. That influence came from the Arctic.

In the GOES image above, we can clearly see a long white arm of cloud stretching all the way down from the Arctic and into Sandy. This arm both greatly increased Sandy’s size and fed her strength through a mechanism called baroclinity. This mechanism fed Sandy’s strength not directly through heat energy alone, but through extreme differences in pressure and temperature. A hot core hurricane met up with a cold core Arctic front tapping the extreme cold air over Greenland. It was this combination of extremes that made Sandy far, far worse. It was this Arctic Arm that pulled Sandy into the East Coast at the most destructive angle possible.

Though scientists didn’t specifically call for the merging of a hybrid system like Sandy, what they did warn us about was how receding Arctic Sea Ice was making severe weather events far more likely. One researcher, Charles Green noted:

“What’s happening now is that we are changing the climate system, especially in the Arctic, and that’s increasing the odds for the negative AO conditions that favor cold air invasions and severe … weather outbreaks.”

Another scientist, Dr. Jennifer Francis also highlighted how Arctic Sea Ice decline would likely result in the kind of blocking patterns that had caused severe weather events in the past. “It’s probably going to be a very interesting winter,” climate scientist Jennifer Francis said in early September in a teleconference with reporters. Francis, a researcher at the Institute of Marine and Coastal Sciences at Rutgers University, has argued that shrinking Arctic ice can be tied to such recent weather events as prolonged cold spells in Europe, heavy snows in the Northeastern U.S. and Alaska, and heat waves in Russia. Francis also noted:

“What we’re seeing is stark evidence that the gradual temperature increase is not the important story related to climate change; it’s the rapid regional changes and increased frequency of extreme weather that global warming is causing. As the Arctic warms at twice the global rate, we expect an increased probability of extreme weather events across the temperate latitudes of the northern hemisphere, where billions of people live.”

In fact, it was Francis’s research that resulted in headlines like this one in the Los Angeles Times on September 13th: “Record loss of Arctic ice may trigger extreme weather” and this one in Climate Progress“How the Arctic Death Spiral Fuels a Wicked Backlash on Our Weather.” On this blog, I posted an article entitled “NOAA’s Global Warning: Arctic Tipping Point Reached, Extreme Weather, Rapid Melt, Ecological Damage to Follow.”

Unfortunately, like so many other global warming Cassandras, these warnings went unheeded. A Presidential campaign in which Mitt Romney bragged about denying climate change and de-funding FEMA made mockery of the science and the altogether salient warnings. Such blindness during a year of record drought and Arctic Sea Ice loss is as inexcusable as it is criminal. Such inexcusable piggishness culminated in a Presidential debate in which Romney goaded Obama into arguing over who could increase drilling and, thus, fossil fuel emissions, the most.

Then came Sandy and now all with eyes to see are able to bear witness to both the new potential for extreme weather and its Arctic Sea Ice melt enabler.

(A graphic of the Arctic blocking pattern that resulted in the Greenland High and Arctic air trough that both added strength to Sandy and helped pull her to shore. Image credit here.)

At issue is the way receding Arctic Sea Ice erodes the circumpolar Jet Stream. This happens as warm air is drawn up from the south, slowing that air current down. The result is that huge wave patterns begin to appear in the Jet Stream. These waves draw warmer air up from the tropics in the south and pull cold air down from the Arctic. The blocking pattern also results in a more frequent negative Arctic Oscillation during the fall and winter months. This negative Arctic Oscillation is associated with extreme winter storms in both the US and in Europe and has been implicated in a number of extreme weather disasters over the past decade and a half.

What happened this year is that withdrawing Arctic Sea Ice likely contributed to a very strong negative Arctic Oscillation occurring this fall. The result was a powerful blocking high pressure system over Greenland and an equally strong cold front pushing down from the Arctic. The fact that this happened at the same time Sandy was making her charge north is not simple coincidence. It is, in part, due to the loading of climate dice that resulted from these factors.

First, we had abnormal late-season heat in the Atlantic fueling a powerful late-season hurricane. Second, we had an abnormally strong blocking pattern establishing early during fall rather than winter. The conditions were set for two powerful storms, should they arise, to come together in a dramatic way. The hot Atlantic Ocean was bound to brew up at least a few more hurricanes. Chances were some of these storms would track close to the troughs pushed south by the blocking Greenland high pressure. The receding Arctic Sea Ice was causing more and more strong cold fronts to charge south. Chances were that one of these might intersect with one of the northward-bound tropical systems.

The deep dig of the charging cold fronts and the blocking high closing off any storm’s egress to the northeast made it increasingly likely that any merged hybrid would come ashore somewhere on the US East Coat. The chances for this set of conditions occurring without climate change eroding sea ice and heating the Atlantic are vanishingly small. But now, with the new conditions established, these events become more and more likely.

At issue here is the fact that these conditions are established now. So we can expect an increasing chance for powerful hybrid storms like Sandy resulting from Arctic and tropical storm mergers as time continues, as Arctic Sea Ice melt intensifies, and as the Atlantic Ocean continues to heat up.


Hurricane Sandy, The Storm that Climate Change Wrought; How Global Warming Made Sandy Far, Far Worse

(Earth. See that massive swirl of clouds with arms stretching up into the Arctic and back across the Atlantic Ocean? Yes, that’s Sandy.)

This year was already the worst extreme weather year ever recorded. Fires, heatwaves, a monster Derecho and a devastating drought together would have made 2012 one for the record books. The one saving grace, it seemed, was that hurricane season hadn’t significantly added to an already severe problem. That was before Hurricane Sandy slammed into the US Northeast causing what many think will be in the range of 10-20 billion dollars in damage. If total damage estimates exceed 20 billion, Sandy will be one of the five most costly hurricanes in US history.

Sandy was nothing if not unprecedented. Never has the Northeast seen this kind of storm so late in the season. Never has New York and New Jersey been subject to such a high level of ocean flooding over such a broad area. According to CNN’s chief meteorologist: “There’s no one that’s not 300 years old that has seen anything like this.” That’s just a finer way of saying that there is no record for a storm like Sandy ever occurring in this region of the country. And, in many cases, there’s no record for a storm like Sandy occurring period.

What made Sandy so unique? In two words: climate change. We’ve seen northeastern Atlantic Ocean storms where powerful troughs combine with hurricanes in ways that create a much stronger storm. The last time such a thing happened was during the 1991 ‘Perfect Storm.’ But that storm formed over the open waters of the Atlantic and only caused damage as it brushed New England with the powerful squall lines and heavy surf it cast off. In the case of Sandy, the Perfect Storm came ashore far further south and west than is usually possible.

Sandy’s Global Warming Ingredients

Since 1991, atmospheric changes and alterations to the Earth’s physical characteristics have been taking place that make storms like Sandy more and more possible. These ‘ingredients’ include increasing ocean temperatures, changes in the jet stream, and the receding boundary of Arctic Sea Ice.

To understand how these changes made it possible for a storm like Sandy to have such a devastating effect on the US Northeast and Mid-Atlantic so late in the season, it helps to follow the life of the storm that became Sandy…

Like so many other hurricanes, Sandy was born of the tropical Atlantic. She started as a pulse of thunderous rain storms swirling off the coast of Africa. This tropical wave slowly gathered energy from the hot tropical Atlantic as she moved west, gradually twisting into the classic coma shape as she entered the central Caribbean.

(GOES weather satellite Image of Sandy from October 22. Sandy is already large for a tropical system. But Sandy will soon grow even larger by combining with other storms to the north.)

Ocean heat content for the South Atlantic and Caribbean was abnormally high this year. Most of this added heat content came from human caused global warming. In many regions, temperatures were 2-3 degrees above average. This meant that, for a storm like Sandy, these waters were about as warm as they would have been two to three weeks earlier during a typical season of the 20th century. This added energy increased the likelihood that the storm would form in the first place. It also gave the storm more capacity to strengthen even in an environment of increased wind shear.

As Sandy tracked northward, she plowed through Jamaica and hopped over the eastern tip of Cuba. Maintaining significant strength as a category two storm, Sandy grew to a large size, boasting a tropical storm wind field in excess of five hundred miles in diameter. Hovering off the coast of Florida, Sandy was about to enter the second stage of her development.

Two systems to the north would play key roles in Sandy’s growth and path. Both were products of new ‘blocking patterns’ that have emerged as regular weather events during the past decade. ‘Blocking patterns’ occur when the jet stream makes deep swoops down from the Arctic and into the mid and lower latitudes. These swoops make giant wave-like patterns in the jet stream. They also create a huge amount of atmospheric inertia. The result is that weather patterns tend to be more persistent. In the under-belly of a blocking pattern, one can expect abnormally hot and dry conditions to persist over long periods of time. In the frontal down-slope of the blocking pattern, one can expect abnormally cool, wet, and stormy conditions. The peaks of these blocking patterns tap the tropics and the troughs tap the Arctic.

According to Dr. Jennifer Francis, these blocking patterns have emerged as a result of sea ice loss in the Arctic. The receding edge of the sea ice pulls air northward changing the shape of the jet stream from that of a rippling halo to that of a circle of sine waves.

The new blocking pattern that had established itself over the central US allowed a powerful cold front to sweep southward, both lending energy to Sandy via strong temperature and pressure gradients and steering Sandy first northward, then pulling her in toward the Mid-Atlantic coast. A second aspect of the blocking pattern emerged in the form of a new high pressure system that has tended to form recently over Greenland. This particular high pressure system blocked the path of Sandy northeastward, shoving Sandy back up against the frontal trough that ended up lending her so much strength.

(A visible satellite shot of Sandy beginning to combine with a powerful Arctic cold front. The massive trough of cold air is outlined in blue. Sandy is in the red circle. To the northeast is a blocking high backing in over Newfoundland. Note the extraordinary size of the combined trough and Sandy.)

As Sandy began to touch the trough’s strong, cooler winds, her tropical storm wind field spread out, eventually reaching 900 miles in diameter. In addition, Sandy found herself cloaked in the trough’s rain shield. This shield helped to prevent the worst effects of wind shear which, at times, was powerful enough to rip a normal storm apart.

Sandy’s encounter with the Arctic-born cold-air trough caused her to explode in size and as she moved north, she pummeled the Outer Banks of North Carolina and Coastal Virginia from 300 miles off shore. What strength she lost at her core was multiplied manifold in the expanding reach of her effect. North Carolina and Virginia coasts experienced impacts usually reserved for those in the direct path of a Hurricane — powerful winds, heavy rains, and storm surge flooding. Roads were washed out, dunes were breached, homes were flooded. Water rises exceeded seven feet in some places.

(Sandy taps hotter than normal Atlantic Ocean water in final rush to the coast. At this point, Sandy is the largest tropical cyclone ever recorded in the Atlantic Ocean.)

Yet Sandy was still hundreds of miles away, biding her time for the final rush to shore. And in this critical time period, global warming again played its hand. Sandy was now moving parallel to the Virginia coast. In normal years, water temperatures would begin to drop off here, sucking energy from the storm. This year, though, water temperatures had heated to 5 degrees Fahrenheit above normal through, the year after year, heat trapping effects of human emitted greenhouse gasses. Sandy drank deep from this added heat and, as the Arctic-born trough began to pull Sandy in to shore, she intensified.

Maximum sustained winds reached 90 mph, tropical storm force wind diameter reached 1000 miles, hurricane force wind diameter reached 200 miles, and the pressure fell to an unprecedented 940 millibars. Sandy was now a storm for the record books. A storm that was the largest tropical cyclone ever to form in the Atlantic. A storm never seen before in this region of the world. A storm powerful enough to push ocean water nearly a mile inland up and down the Jersey coast. A storm mighty enough to create a nearly 14 foot water rise in New York City.

Without climate change, the storm may not have formed in the first place, the storm probably wouldn’t have reached category 2 strength or grown to such a large size, the storm would have not combined with such a powerful trough sweeping so far south, the storm would have not been blocked from going out to sea by the new Greenland/Newfoundland high pressure, the storm would not have strengthened so far north over abnormally hot waters, and the storm would have not been pulled into the coastline by the powerful blocking pattern caused by melting sea ice.

Sandy was, in all ways, the storm that climate change wrought. And since the pattern is now established for this kind of storm to happen now, it is likely that this kind of ‘300 year storm’ will happen again. Almost certainly with growing force and almost certainly within the next decade or two.

I’ll leave you with the following quote from Time Magazine:

“Perhaps, if you are in your 60s or 70s or 80s, Sandy’s destructive forces are a once in your lifetime event. But younger generations—those of us in our fifties, and our children—will likely be looking at flooded coastal cities, devastated infrastructure, blownout power, and storm surges for the rest of our lives.”

(Graffiti scrawled on the side of a house flooded by Sandy. Image credit: here.)


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