Environment Counts | Thawing permafrost will accelerate climate change
Author: Geoff Zeiss – Published At: 2011-12-04 19:36 – (849 Reads)
Arctic temperatures are rising and permafrost is thawing. Carbon released into the atmosphere from permafrost soils will accelerate climate change. This article estimates that permafrost thaw will release the same order of magnitude of carbon as deforestation if current rates of deforestation continue, but because these emissions include significant quantities of methane, the overall effect on climate could be 2.5 times larger.
This recent soil carbon amount is more than three times higher than previous estimates, largely because of the realization that organic carbon is stored much deeper in frozen soils than was thought. Inventories typically measure carbon in the top metre of soil. But the physical mixing during freezeâ€“thaw cycles, in combination with sediment deposition over hundreds and thousands of years, has buried permafrost carbon many metres deep.
The answers to three key questions will determine the extent to which the emission of this carbon will affect climate change:
- How much is vulnerable to release into the atmosphere?
- In what form it will be released?
- And how fast will it be released?
To answer these questions the authors surveyed 41 international scientists, who publish on various aspects of permafrost. The survey asks what percentage of the surface permafrost is likely to thaw, how much carbon will be released, and how much of that carbon will be CH4, for three time periods and under four warming scenarios that will be part of the Intergovernmental Panel on Climate Change Fifth Assessment Report.
- The lowest warming scenario projects 1.5 Â°C Arctic warming over the 1985â€“2004 average by the year 2040 increasing to 2 Â°C by 2100;
- the highest warming scenario posits 2.5 Â°C by 2040 and 7.5 Â°C by 2100.
In all cases, it is posited that the temperature would remain steady from 2100 to 2300.
The collective results suggest that the high warming scenario will degrade 9â€“15% of the top 3 metres of permafrost by 2040, increasing to 47â€“61% by 2100 and 67â€“79% by 2300. The estimated carbon release from the permaforst degradation is 30 billion to 63 billion tonnes of carbon by 2040, reaching 232 billion to 380 billion tonnes by 2100 and 549 billion to 865 billion tonnes by 2300. These values, expressed in CO2 equivalents, combine the effect of carbon released as both CO2 and as CH4.
The survey estimate for the amount of carbon released by 2100 is 1.7â€“5.2 times larger than those reported in several recent modelling studies for a similar warming scenario.
For all of the warming scenarios, most of the released carbon is expected be in the form of CO2, with only about 2.7% in the form of CH4. However, because CH4 has a higher global-warming potential, almost half the effect of future permafrost-zone carbon emissions on climate forcing is likely to be from CH4.
The survey’s estimate for carbon release under the lowest warming scenario is about one-third of that predicted under the strongest warming scenario.
Despite the massive amount of carbon in permafrost soils, emissions from these soils are unlikely to overshadow those from the burning of fossil fuels. However, permafrost carbon release will be an important amplifier of climate change and once the soils thaw, emissions are likely to continue for decades, or even centuries.