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of soil organic carbon contents in the northern circumpolar permafrost region based on the NCSCD (Tarnocai et al., unpublished data, 2007).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 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

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