There's more to global warming than temperature changes and rising seas. Scientists are also finding many subtle side effects.
A new study on forest fires points out one of them. Warmer and longer North American fire seasons have dried out far northern peat bogs so that fire burns where it has been too wet to burn before. These fires release toxic mercury compounds that bogs have absorbed and held safely for centuries.
"We're talking about mercury that has been relatively harmless, trapped in peat for hundreds of years, rapidly being spewed back into the air," says Merritt Turetsky of Michigan State University in East Lansing, lead author of the study published in Geophysical Research Letters. "Our findings show us that climate change is complex."
That complexity is showing up in other ways. Atmospheric scientists, for example, wonder if the increased intensity of Atlantic hurricanes is part of a longstanding natural cycle or due at least partly to man-made global warming.
Last month, James Elsner at Florida State University in Tallahassee published a statistical analysis in Geophysical Research Letters that supports the hypothesis that climate change is indeed influencing hurricane intensity. He warns that, partly because of warming caused by greenhouse gases, hurricane damage will continue to increase.
Scientists also wonder if climate change will release methane, a powerful heat-trapping gas, from natural reservoirs. That could exacerbate global warming. Northern permafrost holds vast amounts of methane. As the permafrost thaws, as some of it now is doing, that gas escapes.
Hydrocarbon seeping up through the sea floor is another methane source. Methane in the seepage bubbles up into the air leaving behind a telltale tar. Tessa Hill at the University of California in Davis and colleagues have been studying deposits of that tar in sediments off California's coast. They reported last week in the online edition of the Proceedings of the National Academy of Sciences that methane releases peaked during periods of climate warming 15,000 and 11,000 years ago.
This finding implies that global warming can enhance methane release from the sea bed. That extra methane in the air can then enhance the greenhouse warming in a kind of feedback effect.
Understanding climatic side effects can give society a heads-up on challenges people may face when their environment no longer does business as usual. For the mountainous regions of North and South America, the side effects of climate change are paramount. Melting glaciers, diminished snow pack, and earlier spring thaws are changing water supplies over large regions. They also are changing what does and doesn't grow at various elevations in the mountains.
Last April, 160 scientists from many of the counties affected met in Mendoza, Argentina, to assess national and international efforts to understand what is happening. Their basic conclusion was that the effects of climate change will be felt in many ways that are only beginning to be understood.