Global Warming Rolls Climate Dice Yet Again: High Amplitude Jet Stream Wave Brings Late July Melt Surge to Greenland

The old cliche is that lightning never strikes twice in the same place. In weather and climate terms, natural variability makes it highly unlikely that record year will follow record year, even when a forcing, such as human global warming, tends to push in that direction.

In the context of Greenland, it was very unlikely that record melt on the order of around 700 gigatons of ice lost during 2012 would repeat in 2013.¬† That said, even in a year like 2013, where climate attempts a return to the average trend line, it’s entirely clear that conditions are anything but normal.

Throughout late June and much of July, a downward dip in the Jet Stream dominated weather patterns over Greenland. Cold, Arctic air was locked over the massive island, pushing melt rates closer to ‘normal’ for a summer season. The term to use is definitely ‘closer,’ because even during weather conditions that would normally bring colder than average conditions to Greenland, warmth and melt were still above average.

Global warming adds a roll

A metaphor we can use to describe this phenomena of implied variability in a warming system is James Hansen’s climate dice. Imagine that a basic roll of a d10 gives us a typical weather pattern for Greenland. 1 on the dice represents record cold, 10 record warmth, 2 and 3 are colder than average, with 2 being near record lows and 3 being closer to average, 4, 5, 6 and 7 are average, 8 and 9 are hotter than average, and 10 is record heat.

This set of weather and climate possibilities is a basic representation of ‘normal’ for Greenland. But when we add in human climate change and global warming, we are essentially adding a new player to the mix, with its own set of dice. In this case, let’s add a 1d3 to the global warming hand. Now, with the extra dice roll for global warming, the potential for extreme hot, melting years just got far, far more likely and we begin to experience never seen before heat and melt events. But we still end up with colder than average years and normal years, just less of them.

The situation is probably worse than the simulation described above because on the typical 1 to 10 scale we can label 2012 about a 13 (with freakish never seen before record heat and melt) and 2013 through about July 26th a 7.1 — slightly hotter than average with ever so slightly above average melt.

The problem is that June and July were average when they should have been cold. I say this because a high amplitude wave in the Jet Stream flowed down over Greenland, pushing relatively colder air over the sea ice and into the freezer that is still Greenland. Such conditions usually push for colder than average Greenland temperatures and lower than average melt. This period of what should have been colder than average conditions instead resulted only in an abatement of record melt and a return to slightly above average melt.

Mangled Jet Stream switches back to ‘hot’

But now, even this brief respite appears to have evaporated. Over the past couple of weeks, the deep, cooler trough over Greenland eroded, weakening as warmer air pushed into southern Greenland. Now, the trough has completely reversed — becoming a ridge and somewhat mimicking the freakish conditions that occurred during 2012. So slightly above average melt conditions are now starting to swing back toward record melt conditions for this time of year.

You can see the large, high amplitude bulge riding from south to north, carrying air from the south-eastern US all the way north to Baffin Bay and southwestern Greenland, in the Jet Stream map for July 30th below:

Greenland Jet

(Image source: California Regional Weather Service)

This sudden Jet Stream switch brings back a weather pattern that caused such major melt conditions during summer of 2012 and such warm winter conditions for Greenland as 2012 turned to 2013. And the results, as far as ice melt goes, have been almost immediate. Earlier melt peaks at around 34% of the ice sheet during July were obliterated in one fell switch of atmospheric air flow that, once again, drew warm, temperate air into the Arctic.

Over the past two days, this extra warmth has increased Greenland melt area to above 40%, peaking at near 45% just a couple of days ago. This peak, though not as anomalous as the 90% + melt coverage experienced during early July of 2012, is still about 80% higher than the average melt peak observed for the period of 1981-2010 and more than double the average for melt in late July. It also puts Greenland further into above average melt year territory, possibly shifting the 2013 score from 7.1 to around 8.5.

You can see the melt coverages graph, provided by NSIDC, for the current year below:

Greenland Melt 2013 Late July

(Image source: NSIDC)

The warm air pulse that drove these anomalously high late season melt rates in Greenland appears to have settled in for at least the time being. Temperatures along the Greenland coast range from the upper 30s to the lower 60s — quite warm for this time of year — while summit Greenland is experiencing warmer than average temperatures in the lower 20s (Fahrenheit).

Above average melt when it should have been cold

So what is freakish about 2013 when compared to 2012 is not that it matched a major melt event that will likely stand as a record for the next five years or so, but that in a year where weather conditions would have pushed Greenland to be mostly colder than normal, above average warmth and melt were still experienced. In this case, it becomes very clear that we are rolling with loaded climate dice or, as the illustration above shows, human global warming is adding its own wicked set of rolls.


California Regional Weather Service


James Hansen’s Climate Dice

Learn about Dark Snow


2012: 9th Hottest Year on Record, Continuation of Inexorable Heating Trend


According to reports from NASA’s GISS division, 2012 was the 9th hottest year on record globally. It was also the hottest year on record for the continental United States. The above image is a composite heat map showing global temperature difference for the 2008-2012 period — a period that has included one hottest year (2010) and two consecutive La Nina years that ranked 2nd and 3rd hottest (2011, 2012). Overall, 2008 was the 12th hottest year on record, 2009 the 7th hottest, 2010 the hottest, 2011 the 10th hottest, with 2012 coming in 9th hottest.

The last year that experienced temperatures cooler than the 20th century average was 1976.


“One more year of numbers isn’t in itself significant,” GISS climatologist Gavin Schmidt said. “What matters is this decade is warmer than the last decade, and that decade was warmer than the decade before. The planet is warming. The reason it’s warming is because we are pumping increasing amounts of carbon dioxide into the atmosphere.”

Given the degree to which heat keeps building up in the atmosphere due to human CO2 emissions, a record 34 gigatons in 2012, it is likely that the next El Nino year will produce a strong new temperature record. However, 2011 and 2012 both experienced La Nina conditions. ENSO conditions are expected to remain neutral throughout much of 2013 with chances rising for a return to El Nino by the end of this year.

NASA scientist James Hansen, who has labeled the ongoing procession of extreme weather events, rapid sea ice melt, glacial melt, and abnormally hot conditions a ‘planetary emergency,’ puts the current state of the human-caused warming trend into perspective:

“The U.S. temperatures in the summer of 2012 are an example of a new trend of outlying seasonal extremes that are warmer than the hottest seasonal temperatures of the mid-20th century,” GISS director James E. Hansen said. “The climate dice are now loaded. Some seasons still will be cooler than the long-term average, but the perceptive person should notice that the frequency of unusually warm extremes is increasing. It is the extremes that have the most impact on people and other life on the planet.”


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