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Carbon Stored in the Arctic Permafrost: What are
the Impacts on the Future Arctic Climate System?
Photo: M. Nigro
Carbon Stored in the Arctic Permafrost
• 1672 Pg of organic carbon is estimated to be stored in
the Arctic permafrost regions of the Northern
Hemisphere (Tarnocai et al. 2009)
• This is 50% of the Earth’s carbon that is stored in below
ground pools
• As the Arctic temperatures increase the extent of the
permafrost declines releasing the stored carbon to the
atmosphere
Where is carbon stored in the Arctic?
• Atmosphere• ~750 Pg globally and ~125 Pg north of 60°N
• Ocean• Cold temperatures in the Arctic increase the efficiency of
carbon transfer from the atmosphere to the ocean• Arctic Ocean is 3% of the Earth’s oceans, but removes 5 to
14% of the Earth’s ocean carbon uptake
• Land• Boreal forest store carbon as plant material
• Sequester about 1.3±0.5 Pg/yr
• Arctic tundra stores carbon as soil carbon• ~1672 Pg in northern permafrost regions
Why do we care about carbon?
Methane (CH4) is 23 times stronger than carbon dioxide (CO2) as a greenhouse gas
What will happen with Arctic warming?
• Permafrost Decomposition & Changes in vegetation
• Methane hydrates
• Photosynthesis
• Droughts and Fires
• Ocean carbon uptake
Permafrost Decomposition & Vegetation Changes
Increased temperatures cause permafrost decomposition
SOURCE: permafrost decomposition releases carbon to the atmosphere
SINK: rising temperatures increases the length of the growing season and bring more productive vegetation to northern latitudes
It is estimated that the release of carbon from permafrost decomposition will be larger than the sink due to changes in vegetation by 1 Pg/year.
Distribution of Soil Organic Carbon
Figure 3. Distribution of soil organic carbon contents in the northern circumpolar permafrost region based on the NCSCD (Tarnocai et al., unpublished data, 2007). Enhanced TIF [3.3 MB]
Methane Hydrates
Methane hydrates: a solid icy form of methane that is trapped in permafrost and at shallow depths in cold ocean sediments
SOURCE: As air and water temperatures increase, the hydrates start to decompose and release methane to the atmosphere
This could take many years, but would have a very LARGE impact
Photosynthesis
Photosynthesis increases with warmer temperatures
SINK: Increased photosynthesis activity will remove more CO2 from the atmosphere
SINK: Increased temperatures will increase the length of the growing season, leading to more photosynthesis
This has an effect over both the land and the ocean
Droughts & Fires
Droughts tend to increase the chance of a forest fire
SOURCE: Forest fires released a significant amount of carbon into the atmosphere
SOURCE: The forest fire destroy plants which uptake carbon from the atmosphere
Fires have an effect on the carbon cycle which lasts much longer than the duration of the fire.
Ocean Carbon UptakeTraditional theory
SINK: As ice melts the newly open water will uptake more carbon from the atmosphere
SINK: Warmer temps increase biological productivity in open water and increase carbon storage as living things die and sink to the ocean floor
SOURCE: Increased temperatures decrease the efficiency of ocean carbon uptake
The traditional view of ocean carbon uptake has been challenged. Studies show that the Arctic Ocean may be “full” of carbon.
Ocean Carbon UptakeRecent Study
Wei-Jun et al. 2010 Science
The increased carbon uptake from newly ice-free regions will be short lived due to a weakening of the carbon gradient between the atmosphere and the ocean. The ocean will quickly reach equilibrium with the atmosphere due to stably stratified waters, surface warming and low biological CO2 fixation.
The traditional view of ocean carbon uptake has been challenged. Studies show that the Arctic Ocean may be “full” of carbon.
Source: ACIA Impacts of a Warming Arctic: Arctic Climate Impact Assessment (2004),Key Finding #2, p.39
Conclusions
It is important to understand the feedback mechanisms involved in the carbon cycle to
make future predictions about the Arctic climate cycle.
Questions?
See me for references
Methane
• Methane produced by decomposition of dead plant material in wet soils (mires and tundra ponds)
• Methane is released to atmosphere when temperature and precipitation are increased
• Methane can be absorbed by forest and tundra soils in very dry conditions
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