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Melting ice in the arctic may change the equation on greenhouse gases

With sea-ice hitting an all-time low in September 2012, scientists are examining how the melt will affect the transfer of greenhouse gases in arctic plant communities.

Melting ice provides some of the most striking images of a changing planet.  The 2012 film Chasing Ice, featuring the work of photographer James Balog and the Extreme Ice Survey, brought attention to the speed and extent of melting in the arctic.  Last year, arctic sea-ice reached its lowest extent in recorded history, half the average extent observed from the 1980s to 2000.  With conditions in the arctic changing rapidly, scientists around the world are investigating how climate change may impact the transfer of greenhouse gases between sea, air, and living things on land.
A study published in Nature Climate Change by an international team of arctic scientists, led by Frans-Jan Parmentier, looked at recent climate change research and impact on Arctic greenhouse-gas exchange. The research tells a troubling story: melting sea-ice may amplify arctic melting.
Melting ice affects a variety of climate factors in the arctic, one of which is the arctic color palette.  Dark-colored melt ponds form on top of light-colored melting ice.  Like a dark tee shirt on a sunny day, dark melt ponds decrease the ice’s albedo, a scientific word for “reflectiveness.”  With less reflection the ice absorbs more heat from the sun, warming the ice just like the dark tee short warms your skin, and more ice melts.  The color palette is changing on land, too. Melting snow and ice leave dark rocks and soil in the sun, again invoking the dark tee shirt affect.
With warmer oceans and land, scientists wonder how arctic plant communities will respond.  Plant communities are important players in regulating climate change, both capturing and emitting greenhouse-gases such as carbon dioxide.  Scientists, however, don't fully understand how melting sea-ice will affect greenhouse-gas exchange in plant communities.  Warmer temperatures will extend the arctic summer, which means plants will have more time to photosynthesize, storing CO2, and to respire, releasing CO2 back into the atmosphere.  Will there be a net change in the balance of CO2 emissions from plants?
Parmentier and his team looked to recent research to try to find an answer to that question.  A 2007 study by led by Stephen Sitch suggests that warmer temperatures will tip the balance towards more CO2 uptake in plant communities. Magnus Lund and a team of researchers set up an experiment in 12 northern-hemisphere wetlands, from warm temperate zones to cold arctic zones, to look at CO2 exchange in plants.  They reason that as temperatures rise the arctic will look more like the temperate zone.  Like Sitch, Lund concludes that higher temperatures and longer summers tip the balance in favor of CO2 storage.  In effect, CO2 uptake by plant communities may mitigate some of the effects of climate change.
Much of the climate change story in the arctic remains unclear.  Scientists are still trying to understand how much arctic plant communities can actually mitigate the effects of global CO2 emissions and ongoing changes in the arctic.  Parmentier also looked at the effect of melting sea-ice on methane emissions from arctic wetlands.  The balance of methane, a greenhouse-gas considered 20 times more potent than CO2, is expected to change, too.  Looking beyond the shore, melting ice and higher temperatures are expected to shift the balance of CO2 exchange in the Arctic Ocean, making the big picture even more elusive.
The results compiled by Parmentier, Sitch, Lund and others contribute to the growing story about climate change in the arctic: change creates more change.  In the complex web of climate change factors, some amplify climate change effects and others reduce the effects.  Bringing the big picture into focus is difficult, but with more knowledge about the interplay of climate change factors, scientists and policy-makers will be able to make better predictions and management decisions in the years to come.



Original Paper:
Parmentier, Frans-Jan W., T.R. Christensen, Lise L. Sørensen, Søren Rysgaard, A. David McGuire, Paul A. Miller, and Donald A. Walker.   2013.  “The impact of lower sea-ice extent on Arctic greenhouse-gas exchange.” Nature Climate Change, vol. 3, pp. 195-202.  DOI: 10.1038/NCLIMATE1784.
Further Reading:
Lund, M., LaFleur, P. M., Roulet, N. T., Lindroth, A., Christensen, T. R., Aurela, M., Chojnicki, B. H., Flanagan, L. B., Humphreys, E. R., Laurila, T., Oechel, W. C., Olejnik, J., Rinne, J., Schubert, P. and Nilsson, M. B. (2010), Variability in exchange of CO2 across 12 northern peatland and tundra sites. Global Change Biology, 16: 2436–2448.  DOI: 10.1111/j.1365-2486.2009.02104.x
Sitch, Stephen, A. David McGuire, John Kimball, Nicola Gedney, John Gamon, Ryan Engstrom, Annett Wolf, Qianlai Zhuang, Joy Clein, and Kyle C. McDonald.  2007.Assessing the carbon balance of circumpolar Arctic tundra using 
remote sensing and process modeling. Ecol. Appl. 17, 213–234.


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