Every few years, the Intergovernmental Panel on Climate Change (IPCC), a group of the world's leading climate scientists, is tasked with explaining the causes and effects of climate change in a comprehensive report.

Yet the science of climate change is evolving more rapidly than the reports can be published. Since the IPCC's latest assessment was released a mere 14 months ago, in November 2007, studies suggest that sea-ice melt, glacier retreat, and food insecurity are all more dire than the IPCC predicted.

One of the greatest changes has been the shrinkage of Arctic ice caps over the past two years. Last month, according to scientists with the U.S. National Snow and Ice Data Center, Arctic sea-ice measured just 12.5 million square kilometers in area, following the second-lowest summertime coverage since recordkeeping began in 1979. The lowest December level on record is 12.4 million square kilometers, measured in 2007.

In comparison, Arctic sea-ice between the winters of 1979 and 2000 averaged 13.4 million square kilometers.

U.K. climate scientists expect 2009 to be warmer than 2008 - and possibly the hottest year since 2005. If true, the upcoming summer Arctic sea-ice coverage may be the smallest ever witnessed.

W.L. Hare, a lead author of the 2007 IPCC report, considers the "master risk" of climate change to be sea-level rise, caused by the melting of land-based ice (such as the Greenland ice cap) and the thermal expansion of sea water.

The 2007 assessment projected that the world's oceans may rise between 0.2 and 0.6 meters by 2100, depending on how much the climate warms.

"We will be lucky to keep sea-level rise below one meter rise within this century, and two meters rise can't be ruled out," said Hare, an environmental scientist with the Potsdam Institute for Climate Impact Research and a contributing author of the new Worldwatch Institute report State of the World 2009: Into A Warming World.

The IPCC also predicted that melting alpine glaciers and evaporating snow cover would accelerate during the 21st century. As a result, many regions will likely experience a decline in freshwater resources and hydropower potential, with redirected seasonal water flows, the report said.

Already, water loss may be occurring more quickly than expected. The United Nations reported in March that glaciers from nine mountain ranges around the world more than doubled their average melting rate between 2004-05 and 2005-06.

"The latest figures are part of what appears to be an accelerating trend with no apparent end in sight," said Wilfried Haeberli, director of the World Glacier Monitoring Service, in a U.N. Environment Programme press release.

With regard to food production, the most recent IPCC report projected that warming temperatures would boost the global agricultural yield when there are "increases in local average temperature over a range of 1-3 degrees Celsius, but above this it is projected to decrease."

A study in the current issue of Science, however, suggests that the IPCC report may have been too optimistic. Researchers conclude that half the world's population may live with food insecurity by 2100 due to climate change. The study asserts with 90 percent probability that by 2100, the lowest growing-season temperatures in the tropics and subtopics will be higher than any temperatures those regions have ever experienced.

"We are taking the worst of what we've seen historically and saying that in the future it is going to be a lot worse unless there is some kind of adaptation," said co-author Rosamond Naylor, a Stanford University economist, in a press release.

The IPCC plans to release its fifth assessment in 2013. Until then, climate scientists, including prominent U.S. scientist James Hansen, have called for a similar report to update the scientific developments. In a open letter [PDF] to U.S. President-elect Barack Obama in December, Hansen suggested that the National Academy of Sciences provide such a study.

"Urgency now dictates a personal appeal," Hansen wrote. "Scientists at the forefront of climate research have seen a stream of new data in the past few years with startling implications for humanity and all life on Earth."

Ben Block is a staff writer with the Worldwatch Institute. He can be reached at bblock@worldwatch.org.

For permission to reprint this article, please contact Julia Tier at jtier@worldwatch.org.