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unpublished data, 2007).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
East Siberian Arctic Shelf
Shakhova et al. 2010 Science
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 Uptake
Traditional 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 Uptake
Recent 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
Credit: Zina Deretsky, National Science Foundation
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
Carbon Dioxide
• CO2 is released during decomposition of soil in
dry areas and forest fires
• Increased temperature leads to faster
decomposition
• Increased temperature causes growth of more
productive vegetation and hence more CO2
uptake