By Charlene Porter
30 January 2014
Washington — If the world acts to reduce carbon dioxide emissions, a melting trend in the Arctic might be slowed in the final decades of this century, according to a new report from U.S. scientists, led by the Pacific lab of the National Oceanic and Atmospheric Administration (NOAA).
Arctic Ocean sea ice and glaciers have melted by 75 percent since the 1980s, according to an article in the American Geophysical Union publication Earth’s Future. Diminishing sea ice at the top of the world offers some of the most compelling evidence anywhere that climate change, global warming and sea level rise are already underway.
Energy companies, the shipping industry, the world’s naval commands and even tourism companies are already reassessing how warming Arctic temperatures will open more sea lanes through the region, allowing greater navigability.
“It is very likely that the Arctic Ocean will become nearly seasonally sea ice free before 2050 and possibly within a decade or two,” according to the article by lead author James Overland of NOAA’s Pacific Marine Environmental Laboratory and a team of co-authors from other U.S. marine and Arctic research centers.
Warming trends are moving faster in the Arctic than in the mid-latitudes for a variety of reasons. The amount of heat the planet surface reflects into the atmosphere is a significant factor. As more bright, white ice melts, more dark sea surface is exposed, absorbing more atmospheric heat, rather than bouncing it back into space. That means, as Arctic sea ice melting accelerates, that trend could speed more warming and more melting.
But this new research indicates that “if civilization follows a mitigation scenario,” for gases contributing to climate change, the mean temperature projections for the Arctic at the end of the century might be 2 degrees to 7 degrees Celsius lower than the temperature rise predictions calculated on the basis of the continued pattern of ongoing increases in global greenhouse gas emissions.
Based on a review of the data, the authors of Earth’s Future project “that major Arctic changes are locked into the climate system over the next decades and that one should consider adaptation as a priority for human response to the changes.”
The authors predict the near-term likelihood of Arctic warming trends with considerable certainty, but what could happen by century’s end is less predictable. The enormous complexity of projecting climate patterns depends on the fundamentally “chaotic nature of the Earth’s climate system” and other variables, which, estimated differently, can lead to considerably different conclusions.
Emission reduction actions versus persistence of current emissions levels are among the variables evaluated by the scientific team.
The contrast between the two different paths shows a “large difference in surface air temperatures in the Arctic for the end of the 21st century, which makes a strong case to begin mitigation activities for greenhouse gases,” according to the conclusions of Earth’s Future.
Arctic-wide temperatures by the end of the century based on climate projections with a business-as-usual emissions policy will increase 13 degrees Celsius in late autumn months and 5 degrees in late spring. Models that calculate a future in which emission reduction policies have taken effect indicate markedly lower seasonal increases of 7 degrees and 3 degrees, respectively.
Other contributors to the article came fom the Joint Institute for the Study of the Atmosphere and Ocean at the University of Washington, the International Arctic Research Center in Fairbanks, Alaska, and the National Snow and Ice Data Center at the University of Colorado, Boulder.