Monday, September 29, 2014

With few data, Arctic carbon models lack consensus

A press release from NASA's Jet Propulsion Laboratory: As climate change grips the Arctic, how much carbon is leaving its thawing soil and adding to Earth's greenhouse effect? The question has long been debated by scientists. A new study conducted as part of NASA's Carbon in Arctic Reservoirs Vulnerability Experiment (CARVE) shows just how much work still needs to be done to reach a conclusion on this and other basic questions about the region where global warming is hitting hardest.

Lead author Josh Fisher of NASA's Jet Propulsion Laboratory, Pasadena, California, analyzed 40 computer models of the amounts and flows of carbon in the Alaskan Arctic and boreal ecosystems. His team found wide disagreement among the models, highlighting the urgent need for more measurements from the region.

Models represent scientists' integrated understanding of Earth processes and systems. They are used both to test that understanding, by comparing their results with real-world observations, and to gain insight into how current trends may affect our planet's future.

"We all knew there were big uncertainties in our understanding, and we wanted to quantify their extent," said Fisher. That extent proved to be greater than almost anyone expected. "The results were shocking to most people," he said.

However, pinpointing the extent and areas of uncertainty is the first step toward reducing them. Fisher noted that he has shared preliminary results with the modelers who participated in the study, and some have already used the results as an opportunity to rethink how they are representing Arctic processes in global models. Moreover, the uncertainty maps that the study produced, showing the specific Arctic regions where the disagreement is greatest, highlight key locations for field campaigns to collect data.

The study, which involved 30 co-authors from around the world, examined how well the models agreed on various factors, such as the rate of plant growth and the amount of carbon exchanged between living things and the atmosphere. They also evaluated the performance of the models against measurements of carbon at monitoring sites along the tundra of the Alaskan North Slope.

"If all the models agree with the observations, uncertainty is probably pretty low. If they wildly disagree, uncertainty is pretty high," Fisher said. "The models were all over the board."....

Tundra in the Russian Arctic on Bolshaya Muksalma Island, shot by Aleksander Kaasik, Wikimedia Commons, under the Creative Commons 3.0 license 

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