Harvard oceanographer James McCarthy talks about the recent climate change report, the controversies surrounding some of its conclusions, and how they compare with his own field observations in the Arctic.

Jennifer Weeks

Humans are undoubtedly causing global temperatures to increase, according to the Intergovernmental Panel on Climate Change (IPCC) in its report [PDF] released Friday. And that will have significant effects, from disappearing ice caps to more frequent droughts.

James McCarthy, professor of biological oceanography at Harvard and co-chair of one of the working groups key to the IPCC’s previous assessment in 2001, spoke with NNB over the weekend about the landmark report.

What’s most significant about the new IPCC report?

Many impacts that were projected in 2001 have now been stated with much greater confidence because the research is stronger and there’s a growing database for comparison. For example, a lot of the 2001 projections about drought, floods, and storms could not be made with any confidence but were stated as likely future consequences. Now the 2007 report cites “observational evidence” of increases in North Atlantic tropical storms.

There was some controversy as the report was being finalized about how it would treat sea-level rise from melting ice sheets. Is the final estimate, that sea level could rise 7 to 23 inches by 2099, credible?

I think the uncertainty was handled adequately. It’s now very clear from six years of data on sea-ice loss that this is not a short-term or local cycle. In the last few years we’ve found that physical instabilities are causing loss of ice in Greenland in ways that were just not imagined in 2001. General-circulation models don’t adequately capture how that contributes to sea-level rise, so the IPCC worded its statement cautiously. However, the report points out that processes “suggested by recent observations” could increase future sea-level rise. For example, a recent Science article that estimated future sea-level rise using a semi-empirical approach instead of modeling found that sea levels could rise faster than projected in the 2001 IPCC assessment.

What impacts have you seen recently out in the field?

On a trip that I led for the Harvard Museum of Natural History last summer, we visited about 10 small villages of 30 people or so on the coasts of Greenland, Baffin Island, and Labrador, and we saw native people’s lives drastically changing. As far back in time as their oral histories go, they’ve had four months each year when they could travel on sea ice to trap and fish, but over about the past 20 years that’s shrunk to two months because sea ice is melting. Their transport is all by dogsled, and both dogs and people live on seals and fish. At some point, when the hunting season gets too short, their entire source of revenue and their subsistence lifestyle will be gone.

We also saw lots of bears stranded on small islands tens of miles from ice, which makes you realize how fragile their existence is in the absence of ice. They can swim tens of miles looking for ice, but not indefinitely.

Are climate change impacts the top research priority for International Polar Year [a major research program starting this year that focuses on the Arctic and Antarctic]?

Climate change will capture the central focus. There are lots of interesting issues, but climate-related questions are really important–for example, the pace of ice loss in Greenland and how marine ecosystems in the Arctic will fare with less ice and more open water. There are some big questions about why the Antarctic hasn’t warmed more and how it plays into the whole global water balance question of ice loss versus ice accumulation.

McCarthy will give a talk tomorrow evening at the Harvard Museum of Natural History on climate change and the International Polar Year.