New Study Finds that Present CO2 Levels are Capable of Melting Large Portions of East and West Antarctica

If you’re a regular reader of this blog and its comments section, you’re probably more than a little worried about two bits of climate science in particular:

Our understanding of past climates (paleoclimate) and 5-6 C long term climate sensitivity.

And if you’re a frequent returner, you’ve probably figured out by now that the two go hand in glove.

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Looking back to a period of time called the Pliocene climate epoch of 2.6 to 5.3 million years ago, we find that atmospheric carbon dioxide levels were somewhat lower than they are at present — ranging from 390 to 400 parts per million. We also find that global temperatures were between 2 to 3 degrees Celsius warmer than 1880s ranges, that glaciers in Antarctica and Greenland were significantly reduced, and that sea levels were about 25 meters (82 feet) higher than they are today.

(The Totten Glacier is one of many Antarctic land ice systems that are under threat of melt due to human-forced warming. A new paleoclimate study has recently found that levels of atmospheric greenhouse gasses that are below those presently in our atmosphere caused substantial Antarctic melt 4.23 million years ago. Image source: antarctica.gov.)

Given that atmospheric CO2 levels during 2017 will average around 407 parts per million, given that these levels are above those when sea levels were considerably higher than today, and given that these levels of heat trapping gasses are rapidly rising due to continued fossil fuel burning, both the present level of greenhouse gasses in the Earth’s atmosphere and our understanding of past climates should give us substantial cause for concern.

This past week, even more fuel was thrown onto the fire as a paleoclimate-based model study led by Nick Golledge has found that under 400 parts per million CO2 heat forcing during the Pliocene, substantial portions of Antarctica melted over a rather brief period of decades and centuries.

Notably, the model found that the West Antarctic Ice Sheet collapsed in just 100-300 years under the steady 400 ppm CO2 forcing at 4.23 million years ago. In addition, the Wilkes Basin section of Antarctica collapsed within 1-2 thousand years under a similar heat forcing. In total, the study found that Antarctica contributed to 8.6 meters of sea level rise at the time due to the loss of these large formations of land ice.

From the study:

We conclude that the Antarctic ice sheet contributed 8.6 ± 2.8 m to global sea level at this time, under an atmospheric CO2concentration identical to present (400 ppm). Warmer-than-present ocean temperatures led to the collapse of West Antarctica over centuries, whereas higher air temperatures initiated surface melting in parts of East Antarctica that over one to two millennia led to lowering of the ice-sheet surface, flotation of grounded margins in some areas, and retreat of the ice sheet into the Wilkes Subglacial Basin. The results show that regional variations in climate, ice-sheet geometry, and topography produce long-term sea-level contributions that are non-linear with respect to the applied forcings, and which under certain conditions exhibit threshold behaviour associated with behavioural tipping points (emphasis added).

This study began the publication process in 2016 when year-end atmospheric CO2 averages hit around 405 parts per million. By end 2017, those averages will be in the range of 407 parts per million. Even more worrying is the fact that CO2 equivalent forcing from all the various greenhouse gasses that fossil fuel burning and related industrial activity has pumped into the atmosphere (methane, nitrogen oxides, CFCs and others) will, by end 2017 hit around 492 ppm.

As a result, though conditions in Antarctica are presently cooler than during 4.23 million years ago, the considerably higher atmospheric greenhouse gas loading implies that there’s quite a lot more warming in store for both Antarctica and the rest of the world. A warming that, even if atmospheric greenhouse gasses remain at present highly elevated levels and do not continue to rise, could bring about a substantially more significant and rapid melt than during the Pliocene.

Links:

Antarctic Climate and Ice Sheet Configuration During Early Pliocene Interglacial at 4.23 Ma

NOAA ESRL CO2 Trends

NOAA’s Greenhouse Gas Index

East Antarctic Ice Sheet More Vulnerable to Melting than We Thought

Pliocene Climate

antarctica.gov

Hat tip to Spike

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“It’s Worse Than We Thought” — New Study Finds That Earth is Warming Far Faster Than Expected

Ocean Heat Map

(Upper ocean heat anomaly map for 2002 through 2011 shows extreme global heating of the upper ocean during the past decade. Image source: Quantifying Underestimates of Long-Term Upper Ocean Warming.)

2 Degrees Celsius. That’s the ‘safe limit’ for human warming now recommended by the IPCC. But under current human greenhouse gas heating of the atmosphere and oceans, 2 C is neither safe, nor the likely final upper limit of the warming we will probably eventually see.

In the push and pull between all the various political and scientific interests over setting these goals and limits, the glaring numbers really jump out at the wary analyst. One is the total heat forcing now being applied to the atmosphere by all the greenhouse gasses we’ve dumped into the air over the years and decades. That total, this year, rose to a stunning 481 parts per million CO2 equivalent. And if we look at paleoclimate temperature proxies, the last time the world’s atmosphere contained 481 parts per million CO2 was when temperatures were in the range of 3-4 degrees Celsius hotter than we see today.

It takes time for all that extra heat to settle in, though. Decades and centuries for ice to melt, oceans to warm and the Earth System to provide feedbacks. So what scientists are really concerned with when it comes to recommending policy is how much warming is likely to occur this century. And, for this measure, they’ve developed a broad science for determining what is called Equilibrium Climate Sensitivity (ECS).

ECS is sensitivity to a given heat forcing that does not include the so-called slow feedbacks of ice sheet and ocean responses. For this measure, 481 ppm CO2e gets us to around 1.8 degrees Celsius warming this Century — if the Earth System and related so-called slow feedbacks are as slow to respond as we hope they will be…

Earth System Warming Far Faster Than Expected

Earlier this week, a new study emerged showing that the world was indeed warming far faster than expected. The study, which aimed sensors at the top 700 meters of the World Ocean, found that waters had warmed to a far greater extent than our limited models, satellites, and sensors had captured. In particular, the Southern Ocean showed much greater warming than was previously anticipated.

Winds and a very active downwelling, likely driven by a combined freshening of water near Antarctica and an increased salinity due to warming near the equator, drove an extraordinary volume of heat into these waters. An extra heat in the oceans that was 24 to 58 percent higher than previous estimates. An extraordinary rate of uptake earlier measures had missed.

Upper Ocean Heat Content trends

(Upper ocean heat content trends from 1970 to 2004. Note the extraordinary amount of heat being forced into the Southern Ocean near the 50 degrees South Latitude line. This heat forcing is likely due to increased storminess and ocean circulation-driven down-welling related to effects driven by human caused climate change such as increased glacial melt in Antarctica and increased sea surface salinity near the equator. Image source: Quantifying Underestimates of Long-Term Upper Ocean Warming.)

This observation led New Scientist to make the following rather blunt statement:

It’s worse than we thought. Scientists may have hugely underestimated the extent of global warming because temperature readings from southern hemisphere seas were inaccurate.

The implications of finding this extra heat are rather significant. For one, it upends current Equilibrium Climate Science. Gavin Schimdt — Chief NASA GISS scientist — over at RealClimate, noted that the study’s findings would increase ECS ranges from 1.1 to 4.1 C to 1.1 to 4.7 C (a 15% percent increase by Gavin’s calculation). This increase shows that the Earth System may well be both far more sensitive to current human heat forcing and may well be likely to warm far faster this century than scientists had previously hoped. For broader context, it’s worth noting that the scientific community generally considers ECS to be in the range of 1.5 to 4.5 C (3 C average). And any analysis of the new findings is likely to push sensitivity to the higher range of these scales.

Dr Wenju Cai from CSIRO in Australia added by noting that the results mean the world is warming far faster than we thought:

“The implication is that the energy imbalance – the net heating of the earth – would have to be bigger,” he says.

Higher rates of Earth Systems responses to human heat forcing this century and a larger net energy imbalance in the global system together spell very bad news. What this means is that there is both more heat forcing now than we at first expected and that that heat forcing is likely to bring about more extreme climate consequences far sooner than we had initially hoped.

These findings are new and will take some time to ring through the scientific community. And though this study provides a more complete picture of how rapidly the Earth is warming and where that heat is going, we are still missing another big part of the puzzle — what is happening to the deep ocean. Recent studies by Trenberth hint that that region of the climate system is also taking up extra heat very rapidly. So, hopefully, more exact measures of the total ocean system can give us an even better idea of how the Earth System is responding to our insults.

Yet again, we have another study showing clearly that conditions are today worse than we previously expected. How we can continue to do things like build coal plants and plan to burn oil and natural gas throughout the 21st Century is beyond imagining. But here we are…

Links:

Quantifying Underestimates of Long-Term Upper Ocean Warming

The World is Warming Faster Than We Thought

Different Depths Reveal Ocean Warming Trends

Climate Responses From Lewis and Curry

Hat Tip to Colorado Bob

Hat Tip to Bassman

CO2, Earth’s Global Thermostat, Dials Up to Record 401.6 ppm Daily Value on March 12

NASA GISS, likely the world’s premier Earth atmospheric monitoring agency has dubbed CO2 “The Thermostat that Control’s Earth’s Temperature.” So when human fossil fuel emissions keep cranking that thermostat ever higher, it’s important sit up and take note. For, inexorably, we keep forcing atmospheric values of this critical heat-trapping gas up and up.

According to reports from The Mauna Loa Observatory and The Keeling Curve, daily CO2 values for March 12 rocketed to a record 401.6 parts per million. Hourly values rose briefly higher, touching 402 parts per million. Levels fell back to around 400 ppm on March 13. But the overall trend will continue upward through March, April and much of May when the height of annual atmospheric CO2 readings is typically reached.

By comparison, during May of last year, daily and weekly values hit just slightly higher than 400 parts per million while measures for the month hovered just below this number. We are now about two months away from the 2014 peak. So it appears possible that daily values could rise to 404 ppm or greater with highs for the month potentially exceeding 402 ppm (you can view a comparison graph for May 2013 here).

March CO2 401.6

(Daily and hourly atmospheric CO2 values from March 7 to 13. Image source: The Keeling Curve.)

Such high levels of this gas have not been seen on Earth in over 3 million years. A time when temperatures were 2-3 degrees Celsius warmer and sea levels were 15-75 feet higher than today. And should CO2 levels merely remain at the level currently achieved, we can probably expect at least the same amount of warming long-term.

CO2 in Context

Annually, the average rate of CO2 increase now is an extraordinary 2.2 parts per million each year. This rate is about 6-7 times faster than at any time in geological history. None of the vast flood basalts of the ancient past, no period of natural vulcanism, can now rival the constant and massive injection of this powerful and long-lasting greenhouse gas by humans into the atmosphere.

Last year, the rate of increase spiked to around 2.5 parts per million and we can view this as mere prelude under a continuation of business as usual. For if human fossil fuel emissions are not radically brought into check, the ongoing economic inertia of existing fossil fuel based infrastructure and planned new projects will likely shove this rate of increase to 3, 4 even 7 parts per million each year by the end of this century. As a result, CO2 levels alone have the potential to reach catastrophic values of 550 parts per million by around 2050-2060 that, long term and without any of the added effects of other greenhouse gasses, would be enough to eventually melt all the ice on Earth and raise global temperatures to around 5-6 degrees Celsius above current levels. A level that, through acidification alone and not including damage through stratification and anoxia, could drive up to 1/3 of ocean species to extinction.

CO2 accounts for much of the greenhouse forcing when taking into account the feedbacks it produces on water vapor and clouds. NASA notes:

Because carbon dioxide accounts for 80% of the non-condensing GHG forcing in the current climate atmosphere, atmospheric carbon dioxide therefore qualifies as the principal control knob that governs the temperature of Earth.

All other greenhouse gasses pale in comparison to both its total effect and its current rate of increase. Methane, the next most potent greenhouse gas, accounts for about 15% of the forcing and is rising at a rate of 4 parts per billion (1/550 that of CO2), generating a net effect equal to, in the worst case, an additional .4 parts per million CO2 each year (.29 when aerosols drop out). A troubling and dangerous increase itself. But still a mere shadow compared to the overall rate of CO2 increase.

Only in the most catastrophic of scenarios, when added atmospheric heat, primarily generated through added CO2 and other greenhouse gas forcing, triggers methane emissions equal to 2 gigatons each year in the Arctic (a rate 25 times the current release), would the total methane forcing approach the predicted value for CO2 by the end of this century under current fossil fuel emissions scenarios. More likely, paleoclimate scenarios tend to suggest that the natural methane feedback, long-term, is roughly equal to 50% of the CO2 forcing and is largely governed by it. A dangerous amplifying feedback driven by a devastating and long-lasting CO2 forcing.

CO2 is also the longest lived of the major greenhouse gasses with one molecule of CO2 providing effective atmospheric warming for at least 500 years. By comparison, the oxidation time for a single molecule of methane is around 8 years. What this means is that it takes an ever increasing methane emission just to keep values constant while atmospheric CO2 takes much longer to level off given even a constant rate of emission.

The result is that heat forcing from CO2 tends to remain constant over long periods while methane heat forcing values have a tendency to spike due to rapid oxidation.

methane.rf_.11071836-300x150

(Radiative forcing from a 10 gigaton release of methane in red compared to expected end century CO2 values of 750 ppm. Note how the methane heat forcing spikes and then rapidly falls off. Image source: RealClimate.)

Current rates of CO2 increase, therefore, should be viewed as catastrophic to climates that are both livable and benevolent to humans. A rate of increase that puts at risk severe changes to Earth environments and which provides a trigger for setting off a series of powerful amplifying feedbacks through the medium and long term. These include both loss of ice albedo and the potential for spiking methane emissions from the widespread natural store.

UPDATE:

Most recent daily values from March 12 onward in relationship to the six month trend. Note the sharp spike upward at the end of the period as well as the overall volatility of the trend line. High volatility may well be an indication that the typical carbon cycle is suffering disruption with sinks, stores and sources experiencing larger than typical fluxes.

mlo_six_months

(Mauna Loa Observatory six month trend. Image source: The Keeling Curve.)

Dr. Ralph Keeling today noted:

“We’re already seeing values over 400. Probably we’ll see values dwelling over 400 in April and May. It’s just a matter of time before it stays over 400 forever.”

Links:

The Keeling Curve

May 2013: CO2 Touches 400 ppm

The Thermostat that Control’s Earth’s Temperature

Atmospheric Composition, Radiative Forcing, and Climate Change as a Consequence from the Massive Release of Gas Hydrates

RealClimate

Hat Tip to Climate State

Kudos to Mark Archambault for Looking Sharp

“Slow Feedbacks,” Paleoclimate Data Show Equilibrium Climate Sensitivity Misses Half of Future Warming

Over the past month or so, there’s been quite a bit of controversy over a scientific measurement called equilibrium climate sensitivity (ECS). Among the media, confusion abounds. In a recent instance, The Economist, taking a number of scientific studies out of context, made the dubious claim that a slower pace of temperature increase during the first decade of the 20th century indicated a lower level of climate sensitivity. Other news outlets continue to remark on new climate sensitivity studies without appearing to understand what equilibrium climate sensitivity really means or, more importantly, understanding the inherent limitations of model-based ECS estimates.

Because there’s been such a high level of interest in and confusion over ECS recently, it’s worthwhile taking a closer look at this measurement’s scope and limitations. In an effort to clear up some of the confusion surrounding ECS, this article will attempt to answer these questions:

  • How is ECS defined?
  • How accurate is ECS?
  • And, lastly, does a slower pace of warming over the first decade of the 21rst century mean climate sensitivity is less than previously expected?

Definition of Equilibrium Climate Sensitivity

In its broadest sense, ECS defines the long-term increase in surface air temperatures that results from a doubling of atmospheric carbon dioxide. The measure is important because it gives a broad indication of how much climate change and related harm to humans and environments results from a given amount of carbon dioxide being pumped into Earth’s atmosphere.

Under these basic principles, ECS provides a good guideline. However, ECS operates under a major handicap. The measurement does not include the effects of slow climate feedbacks like loss of ice sheets or albedo change to Earth’s surface.

How Accurate is Equilibrium Climate Sensitivity?

Because ECS leaves out slow feedbacks, it isn’t a very accurate measure of potential long-term warming. That said, in the early days of global warming modeling, ECS was seen as the most useful measure because models had difficulty handling complex physical forces that resulted from slow feedbacks. The result was that climate science came to rely on a less accurate measure because it was more expedient to use in modeling.

For these reasons, ECS was developed as a simpler way to model atmospheric temperature increase caused by carbon emissions over the long term. And because it was difficult to model slow feedbacks, they were not included in the measurement. So, though ECS is a useful measurement for the purposes of more easily modeling atmospheric temperature increases, ECS dramatically undershoots long-term global temperature increases.

The reason for this is that slow feedbacks such as albedo change and ice sheet melt have powerful impacts. We know this because ECS models tend to present about half the total sensitivity observed in the paleoclimate data for a doubling of CO2. This second and more accurate, but far more difficult to model, measure of climate sensitivity based on all global feedbacks acting in concert is called Earth System Sensitivity (ESS).

In total, the combined Earth System Sensitivity is far greater than the more model friendly Equilibrium Climate Sensitivity. By how much? Based on paleoclimate data, total long term ESS is probably about double that of current ECS estimates.

Muddling Models

Unfortunately, these different definitions can be very confusing to the layman observer. As an example, the IPCC estimates ECS to be between 1.5 to 4.5 degrees Celsius for each doubling of CO2. From an average of these measures, the IPCC gets its estimate ECS of about 3 degrees Celsius. On the other hand, observations of past Earth climates show temperatures averaging at least 6 degrees Celsius warmer when CO2 levels were around 560 parts per million, or about double what the IPCC estimates for ECS.

Yet ECS is, most often, the official, published estimate for how much the Earth will warm. Yet, as shown above, given our current understanding of past climates, the ECS model estimates are short by half.

When looking at the stunning impact of CO2 on global temperatures in the paleoclimate data, one wonders why ECS is used, so often, without this broader qualification? Why, instead, don’t estimates of ECS provide a broader indication that end temperature increases are likely be double those seen in the climate models?

Lower Climate Sensitivity?

For the most part, scientists are trying to determine if slower atmospheric warming since 2000 indicates that climate sensitivity, in this case an already, short by half, equilibrium climate sensitivity, is less than previously expected.

For context, average atmospheric temperatures increased by about .2 degrees Celsius during the 1990s while atmospheric temperatures during the 2000s increased by about .1 degree Celsius. This apparent slowdown in atmospheric warming has caused some to question whether equilibrium climate sensitivity is less than previously expected.

One paper, published by Alexander Otto in Nature indicated a long-term equilibrium climate sensitivity of about 2 degrees Celsius based on new data from recent decades. This new model estimate is still in the range of 1.5-4.5 degrees Celsius provided by most model runs. Furthermore, the study found almost no significant changes to equilibrium climate sensitivity in the long-term trend.

Another Nature study, conducted by Roger Bodman of Victoria University, also found that model estimates for equilibrium climate sensitivity were not lower than previous estimates.

Conclusions

The conclusions to draw from this information are manifold.

The first is that model estimates for equilibrium climate sensitivity are not the best measure of total, long-term climate change. For that we should take a look at past Earth climates. From these measurements, we can find an Earth System Sensitivity of about 6 degrees Celsius for each doubling of CO2. This measure is consistent with Earth climates 50-65 million years ago when CO2 measured about 580 parts per million and temperatures were more than 6 degrees Celsius warmer.

The second conclusion is that long-term change will likely take many centuries to completely unfold. So long-term climate sensitivity measures like ECS or ESS are not good indicators for how fast Earth temperatures will increase within a given decade. Some decades may see relatively slow increases, some little or no increase, and some remarkably rapid increases. However, the overall trend will be for warming, and probably a more rapid pace of warming than that seen in the geological record due to the fact that the human CO2 forcing is currently so powerful.

Furthermore, the .2 degrees Celsius warming during the 1990s and the .1 degrees Celsius atmospheric warming during the 2000s are not entirely indicative of what the long-term trend will look like. In all likelihood, natural variability favored warming more during the 1990s and less so during the 2000s. This is hinted at in the El Nino/La Nina cycle with many powerful El Ninos (which tend to warm the atmosphere) evident during the 1990s while La Ninas (which tend to cool the atmosphere) were more prevalent during the late 2000s.

The third conclusion is that major Earth system feedbacks are beginning to kick in that are likely to make observations of the climates of past decades less relevant. Loss of albedo, ice sheet melt, ocean heat uptake, and environmental carbon release all have a roll to play in future atmospheric warming. Together with a continued and growing human CO2 forcing, these and other factors will determine the pace of warming over the next century. Under business as usual, worldwide CO2 levels hit somewhere between 800 and 1000 parts per million by the end of this century. Such a strong forcing is likely to have very powerful and damaging effects on Earth’s climate system. Even the models that do not take into account slow feedbacks are showing warming of 5-7 degrees Celsius by the end of this century if business as usual emissions continue. And for such a high degree of warming to take place even without the additional contribution from a number of slow feedbacks would be a terrible result.

Fourth, it should be noted that ‘slow feedbacks’ are already beginning to emerge at a more rapid pace than previously estimated. One example, loss of sea ice, is already reducing the northern polar region’s albedo. Another instance, methane hydrate and tundra methane release, are also already adding a positive amplifying feedback to human-caused warming.

Finally, it is worth noting that a more rapid than expected melt of polar ice would temporarily keep temperatures lower at the cost of a more rapid pace of sea level rise combined with much more extreme weather. Such higher than expected paces of melt are entirely possible and, in certain regions, appear to be happening now. In one example northern polar sea ice has experienced an 80% loss of volume since 1980. The result is that northern hemisphere sea ice melt is occurring 80 years ahead of model projections.

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