How will permafrost affect and be affected by global environmental change?

Permafrost is defined as ground that remains at or below 0°C for at least two consecutive years. Permafrost underlies approximately 25 % of the land area in the northern hemisphere and can be up to 1500 m thick. Under current climate-change scenarios, permafrost degrades from both the top and bottom, increasing the depth of the “active layer”, and the extent of talik formation.

The deepening of the active layer could trigger the massive decomposition of organic matter stored in the first three meters below surface. The most recent estimates put the organic carbon pool in permafrost at 50% of the global soil organic carbon pool. This pool is equivalent to twice the amount of carbon in the atmosphere. The decomposition processes would lead to the emission of vast quantities of greenhouse gases, including methane and carbon dioxide, which could greatly affect the global climate.

Under the sea, permafrost occurs as subsea permafrost. Its presence on Arctic shelves is intrinsically linked to the occurrence of gas hydrates which are released to the atmosphere through “holes” in the permafrost, called gas seeps. Its exact distribution on the shelves of the Arctic has not yet been correctly assessed, which hampers the attempts to correctly depict the mechanisms of gas hydrate occurrence and release.

In alpine areas, permafrost is responsible for the occurrence and the preservation of landforms that could evolve dramatically, resulting in large scale natural hazards for alpine valley settlements. In the Arctic, rapid coastal erosion of permafrost is expected to increase dramatically following the drastic reduction of summer sea ice extent, threatening the existence of Inuit communities.

Permafrost observation and monitoring is probably one of the most important challenges of the twenty-first century

More information on theIPA website

What is the exact sensitivity of the climate system to changing greenhouse gas, dust and aerosol loading in the atmosphere?

The IPCC AR4 has shown that, although we understand better and better how the climate system works, there are still considerable uncertainties in evaluating its future evolution. Not only due to uncertainties in human emissions, but also because of flaws in our physical and biogeochemical understanding of the system. The unpredicted recent evolution of Arctic sea ice or of the Greenland ice sheet are magnificent examples of such flaws.

Although everyone legitimally wants to understand the impacts of climate change (which drives many other global changes such as water resources, biodiversity, agriculture, extreme events, etc…), or wants to develop strategies of mitigation and adaptation to global change, there is little hope in doing a good job in the two latter aspects of global change if one does not improve our physical understanding of the system.

Climate sensitivity is the clear prerequisite to all other physical aspects such as tipping points, feedbacks, thresholds, etc… Solving this question allows one to basically improve the response to all other questions, from the physics to the mitigation, going through the impacts.

How extensive will be the reorganization of the planet’s climate system and northern ecosystems in response to an 80% loss in summer arctic sea ice cover over the next few decades?

Arctic sea ice loss is happening at least 30 years earlier than anticipated by the IPCC AR4 Report. The arctic ocean is gaining excess heat which is already being given back to the atmosphere in the autumn and thus changing the winds down into the northern mid-latitudes and the northern part of the earth’s heat engine. We have lost 40 % of summer sea ice already; this impact will only increase as we lose 80 % of the summer sea ice over the next few decades.

How and why is the cryosphere changing? How are these changes impacting people and eco-systems around the planet? What can be done to ameriolate these changes?

The cryosphere is one of the most dynamic, least sampled and least understood components of the Earth system. Changes in the cryosphere impact the water supply for millions, if not billions of people on the planet and seriously alter the availability of water for industry, irrigation, consumption and sanitation. Changing sea level *will* impact those on the coast, changes in seasonal snow cover will impact regional climate and the Earths albedo. Changes in the Earths polar ice sheets are alarming, but not yet fully understood. Changing ice and snow affects all other aspects of the Earth system – ecology, geology, hydrology, atmospheric science, marine systems, social systems, economic systems and human health. We cannot ignore the cryosphere. Obstacles – perceived relevance to the science funding agencies of tropical countries, politics of high latitudes, resource management challenges. In my opinion decreasing water supplies will be the cause of future international tensions.