Permafrost

The Great Siberian Thaw 0122.rtf - In-depth history and analysis

Large Loss of CO2 in Winter Observed across the Northern Permafrost Region - Summary 1019.rtf

Permafrost Is Warming Around the Globe, a Problem for Climate Change 0119.rtf

     About 24% of Northern Hemisphere land surface was covered by permafrost in 1997.  See north polar-view map at left.  Soil carbon content tends to be greater toward the poles, where permafrost is most prevalent (and probably deeper).

Permafrost: MacDougall

Changes in the size of each Earth system carbon pool in response to the addition of permafrost carbon to the UVic ESCM.

     That is, the difference in the size of each carbon pool between simulations with and without permafrost carbon.  All values are relative to the size of the frozen permafrost carbon pool.  A summation of all the pools adds up to 100% for each year.

     Results are given for two emissions pathways (DEPs 4.5 and 8.5) and for 3 climate sensitivities to a doubling of CO2 (2.0, 3.0, and 4.5°C).  Soil layers that thaw, but are subsequently returned to a permafrost state, continue to be administered by the active soil carbon pool, leading to the apparent high rate of transfer of carbon to the active soil carbon pool in the 20th century.

     Permafrost (not including whatever is under the ice in Greenland and Antarctica) holds about twice as much carbon as the atmosphere does today.  In the worst case shown, if current net carbon sinks fail, atmospheric CO2 levels could double from permafrost alone.  Then add the effect of human carbon emissions.

     Strangely enough, the additional temperature effect of permafrost emissions is not highest in the highest human emission scenario (DEP 8.5), but in the intermediate scenarios.  The simplest reason is that CO2 in the air warms the air at a diminishing rate; with more CO2 molecules in the air, the chances are higher that one at a lower altitude will intercept outgoing radiation before one at a higher altitude gets a chance.

MacDougall Permafrost Carbon Emissions, Supplement 0912.pdf

Graphs of modeled future permafrost extent anomaly in CO2 concentration with respect to baseline runs with no permafrost carbon, for each DEP.  Which climate sensitivity is assumed in not clear.

Thawing Permafrost to Double Carbon in Air 0113.rtf - summary of study below

Antarctic May Host Methane Stores 0812.rtf

     "Between about 55.5 and 52 million years ago, Earth experienced a series of sudden and extreme warming events (hyperthermals) superimposed on a long-term warming trend.  The first and largest of these events ... (PETM) is characterized by a massive input of carbon, ocean acidification and an increase in global temperatue of about 5°C within a few thousand years."
    "...the magnitude and timing of the PETM and subsequent hyperthermals can be explained by the orbitally triggered decomposition of soil organic carbon in circum-Arctic and Antarctic terrestrial permafrost.  This massive carbon reservoir had the potential to repeatedly release thousands of [billions of tonnes] of carbon to the atmosphere-ocean system, once a … threshold had been reached...."

    "These results show the potential for high-latitude climate forcing to trigger massive terrestrial carbon release, initiating positive warming feedbacks that can account for the sudden and high elevations of past hyperthermals."

(Xerophytic plants, such as cactus, are adapted to live with very little water.)

     At 400 ppm (not shown), global mean surface temperature is ~14.6°C, about the same as today.  At 900 ppm CO2 (top & middle 4 panels of 6), global mean surface temperature is 6°C warmer than today and Antarctic summers are too warm to allow glaciation.  But ~9/10 as much permafrost remains in high latitudes of both hemispheres (top panel, not middle) as in Earth's total modern inventory, NOT counting modern Greenland and Antarctica, where most permafrost was then.
    In the model, the warming-permafrost positive feedback loop eliminates 97-98% of the initial permafrost inventory (bottom 2 panels), releasing ~3,400 billion tons af carbon within 10,000 years [~10 times what humans have released from fossil fuels].  This raises global mean surface temperature another 6°C, leaving 2,680 ppm of CO2 in the air (see bottom left panel).

     In the bottom panel, which features 2,680 ppm CO2 and is ~12°C warmer than today, dry vegetation types (scrub and cactus) cover most of Africa (replacing much savanna), South America (replacing savanna and tropical deciduous woodland), and Southeast Asia (replacing tropical broadleaf forest).  Warm and temperate deciduous and mixed deciduous-conifer forests cover much of Antarctica and most of Siberia and Canada, replacing most cold conifer forests.

Section Map: Carbon Emissions