- Current levels of atmospheric carbon dioxide are probably sufficient to trigger large-scale permafrost carbon feedbacks and global warming that human effort would be unable to contain.
- The time to slash emissions was a long time ago but now is still much, much better than later, which may, as new studies suggests, simply become too late.
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| Thawing permafrost |
The last time carbon dioxide levels were apparently as high as they are today — and were sustained at those levels — global temperatures were 3 to 6 degrees Celsius higher than they are today, the sea level was approximately 25 to 40 metres higher than today, there was no permanent sea ice cap in the Arctic and very little ice on Antarctica and Greenland.
One impact is ocean acidification (increasing atmospheric carbon dioxide is well-mixed with the ocean, to form carbonic acid and thus increasing water acidity) and rising ocean temperatures. Given that carbon dioxide emissions over the next two decades are being determined (more than we would wish!) by existing energy infrastructure, we are not far from disaster:
- Oceans are more acidic than they have been for at least 20 million years, and they are acidifying 10 times faster today than 55 million years ago when a mass extinction of marine species occurred. It is predicted 10 per cent of the Arctic Ocean will be corrosively acidic by 2018, and 50% by 2050.
- By 2030 (with atmospheric CO2 around 450ppm) the Southern Ocean will have reached a tipping point; and tiny pteropods at the base of the food chain in the southern ocean are likely to have hit a tipping point where they can no longer maintain their shells, says Dr Donna Roberts of the University of Tasmania.
- In January 2010, the prestigious journal Nature reported that scientists have found a 40 per cent decline in phytoplankton since 1950 linked to the rise in ocean sea surface temperatures. Phytoplankton are the foundation of the marine food chain, suck up harmful carbon dioxide and produce half the world’s oxygen. This may be the most devastating impact yet documented of human-caused global warming.
- And in June 2011 a global panel of scientists concluded that marine life facing mass extinction "within one human generation".
So the big question is how far we are from triggering large-scale permafrost release.
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| PIOMAS yearly minimum Arctic ice volume (click to enlarge) |
- The first point to note is that the Arctic has already proved to be more sensitive to global warming that expected. It is now acknowledged that the Arctic has passed the tipping point for sea-ice-free summers. The lack of summer sea-ice will increase Arctic warming (already double the global average) as heat-reflecting ice is replaced by dark, heat-absorbing open seas. There may well be a summer sea-ice-free Arctic by around 2015 (see chart).
- Those circumstances will increase the rate of melting of the Greenland ice sheet, which is already accelerating. And now the tipping point for Greenland's ice sheet (eventual sea level rise of 7 metres) has been revised down from around 3 degrees C to just 1.6C (uncertainty range of 0.8C-3.2C). At the current temperature rise of 0.8C we may have already reached Greenland's tipping point, and with temperature rises in the pipeline (global emissions still rising, no reasonable agreement to reduce them), we are very likely to hit 1.6C in two to three decades.
- Global average temperatures have warmed just less than 1ºC since the Industrial Revolution, but average temperatures in Siberia, Alaska and western Canada are now 3ºC to 4ºC warmer than 50 years ago. In parts of northern Canada, Greenland and the surrounding ocean during the 2010-2011 northern winter, temperatures were more than 6 degrees Celsius warmer than the baseline temperature average for the period of 1951-1980, and 7 to 9 degrees Celsius above average over the Chukchi Sea. So by mid-century the regional increase increase could easily be 4ºC to 6ºC.
- Predictions in 2011 suggested that as soon as 2020 carbon emissions from melting permafrost could be close to a billion tonnes a year. Researchers said that this positive permafrost carbon feedback will “will change the Arctic from a carbon sink to a source after the mid-2020s and is strong enough to cancel 42–88% of the total global land sink.”
- Work by Celia Bitz, Philippe Ciais and others suggests that the tipping point for the large-scale loss of permafrost carbon is around 8–10C regional temperature increase. As temperatures rise, it is projected that Arctic amplification (the multiple by with the Arctic warms compared to the global average) would be approximately times three, so around a 3C increase in global temperature is probably more than enough to detonate the permafrost timebomb. This feedback in the carbon cycle would drive temperatures significantly higher. Caias told the March 2009 Copenhagen science conference that: “A global average increase in air temperatures of 2C and a few unusually hot years could see permafrost soil temperatures reach the 8C threshold for releasing billions of tonnes of carbon dioxide and methane”.
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The take-home message is that current levels of atmospheric carbon dioxide are probably sufficient to trigger large-scale permafrost carbon feedbacks and global warming that human effort would be unable to contain.
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| In the Pliocene 3 million years ago conditions were 11-16 degrees Celsius warmer, at atmospheric carbon dioxide levels similar to today. |
Similar dynamics are at play today. Global warming is degrading permafrost in the north polar regions, thawing frozen organic matter, which will decay to release CO2 and methane into the atmosphere. This will only exacerbate future warming in a positive feedback loop.Here's more on the new study from Joe Romm's Climate Progress:
Nature Bombshell: ‘Past Extreme Warming Events Linked To Massive Carbon Release From Thawing Permafrost’
So begins an article in the journal Nature that offers an unsettling explanation for one of the great climate mysteries: What caused the PETM? The article’s title gives away the answer: “Past extreme warming events linked to massive carbon release from thawing permafrost” (subs. req’d).The lead author, climate scientist Rob DeConto, explains in a news release:
The standard hypothesis has been that the source of carbon was in the ocean, in the form of frozen methane gas in ocean-floor sediments,” DeConto says. “We are instead ascribing the carbon source to the continents, in polar latitudes where permafrost can store massive amounts of carbon that can be released as CO2 when the permafrost thaws.Indeed, the recent scientific literature suggests that the permafrost is poised to be a major amplifying feedback if we are self-destructive enough to ignore yet another dire warning and stay anywhere near our current path of unrestricted carbon pollution:
The new view is supported by calculations estimating interactions of variables such as greenhouse gas levels, changes in the Earth’s tilt and orbit, ancient distributions of vegetation, and carbon stored in rocks and in frozen soil.
While the amounts of carbon involved in the ancient soil-thaw scenarios was likely much greater than today, implications of the study appear dire for the long-term future as polar permafrost carbon deposits have begun to thaw due to burning fossil-fuels, DeConto adds. “Similar dynamics are at play today. Global warming is degrading permafrost in the north polar regions, thawing frozen organic matter, which will decay to release CO2 and methane into the atmosphere. This will only exacerbate future warming in a positive feedback loop.”
- Nature: Climate Experts Warn Thawing Permafrost Could Cause 2.5 Times the Warming of Deforestation!
- NSIDC: Thawing permafrost feedback will turn Arctic from carbon sink to source in the 2020s, releasing 100 billion tons of carbon by 2100
In short, whatever we do, we don’t want to duplicate the conditions of the PETM. But, tragically, we are. Indeed, a 2011 study that found humans are releasing carbon to the atmosphere 10 times faster now than during the PETM. “Rather than the 20,000 years of the PETM which is long enough for ecological systems to adapt, carbon is now being released into the atmosphere at a rate 10 times faster,” one of the authors of that study explained. “It is possible that this is faster than ecosystems can adapt.”
Here’s more on this important new study:
[DeConto] and colleagues at Yale, the University of Colorado, Penn State, the University of Urbino, Italy, and the University of Sheffield, U.K., designed an accurate model―elusive up to now―to satisfactorily account for the source, magnitude and timing of carbon release at the PETM and subsequent very warm periods, which now appear to have been triggered by changes in the Earth’s orbit.The time to slash emissions was a long time ago but now is still much, much better than later, which may, as this study suggests, simply become too late.
Earth’s atmospheric temperature is a result of energy input from the sun minus what escapes back to space. Carbon dioxide in the atmosphere absorbs and traps heat that would otherwise return to space. The PETM was accompanied by a massive carbon input to the atmosphere, with ocean acidification, and was characterized by a global temperature rise of about 5 degrees C in a few thousand years, the researchers point out. Until now, it has been difficult to account for the massive amounts of carbon required to cause such dramatic global warming events.
To build the new model, DeConto’s team used a new, high-precision geologic record from rocks in central Italy to show that the PETM and other hyperthermals occurred during periods when Earth’s orbit around the sun was both highly eccentric (non-circular) and oblique (tilted). Orbit affects the amount, location and seasonality of solar radiation received on Earth, which in turn affects the seasons, particularly in polar latitudes, where permafrost and stored carbon can accumulate.
They then simulated climate-ecosystem-soil interactions, accounting for gradually rising greenhouse gases and polar temperatures plus the combined effects of changes in Earth orbit. Their results show that the magnitude and timing of the PETM and subsequent hyperthermals can be explained by the orbitally triggered decomposition of soil organic carbon in the circum-Arctic and Antarctica.
This massive carbon reservoir at the poles “had the potential to repeatedly release thousands of petagrams of carbon to the atmosphere-ocean system once a long-term warming threshold was reached just prior to the PETM,” DeConto and colleagues say. Until now, Antarctica, which today is covered by kilometers of ice, has not been appreciated as an important player in such global carbon dynamics.
In the past, “Antarctica and high elevations of the circum-Arctic were suitable locations for massive carbon storage,” they add. “During long-term warming, these environments eventually reached a climatic threshold,” with permafrost thaw and the sudden release of stored soil carbon triggered during the Earth’s highly eccentric orbits coupled with high tilt….
Overall, they conclude, “an orbital-permafrost soil carbon mechanism provides a unifying model accounting for the salient features of the hyperthermals that other previously proposed mechanisms fail to explain.” Further, if the analysis is correct and past extreme warm events can be attributed to permafrost loss, it implies that thawing of permafrost in similar environments observed today “will provide a substantial positive feedback to future warming.”
