Nature responds to warming signs
If you're wondering whether the climate really is changing, consider the midges and be wise. In some remote North American mountain lakes, cold-water forms of these tiny insects have given way to warm-water species. This is one of several recently announced findings that indicate climate change is being felt in diverse ways.
Microscopic plants called phytoplankton are becoming less productive as surface water warms over vast areas of the ocean. Extreme rainfall events are increasing over India as the environment warms. These trends highlight the need to adapt to changes already under way even while debate continues over the extent to which humans are jiggering the climate.
Midges aren't waiting. David Porinchu at Ohio State University in Columbus and colleagues discovered this when they traced the history of midge populations in six small lakes in the Great Basin of the western United States. Dr. Porinchu told a meeting of the American Geophysical Union in San Francisco last week that sediments record a shift from cold-water to warm-water midge populations in these remote lakes over the past 25 years. "Climate change has had an overriding influence on the composition of the midge communities within these lakes," Porinchu concludes. Lake water has warmed less than 1 degree C. Yet that's enough to stir the temperature-sensitive insects to adapt.
Climate change is not so benign for the Indian subcontinent. Three weeks ago, B.N. Goswami at the Indian Institute of Science in Bangalore and colleagues reported an analysis of monsoon seasons from 1951 to 2000. As described in the journal Science, their work shows what they call "significant rising trends in the frequency and magnitude of extreme rain events." Total seasonal rainfalls have not changed because there is a balancing decline in light to moderate rain events. But the changes in rainfall timing and the severe flooding caused by extreme events can hurt farming and destroy villages. The researchers expect these trends to continue as the climate warms.
Michael Behrenfeld at Oregon State University in Corvallis and colleagues have studied nine years of satellite data showing phytoplankton productivity over ocean areas. These tiny plants underlie marine food chains. They are a vital component of Earth's ecological system supplying much of the air's oxygen, among other services. Scientists can't yet predict how global warming may affect overall marine productivity. They need to know more about the links between climate change and Earth's biological systems. Dr. Behrenfeld's team has taken a major step toward that understanding. They explained two weeks ago in Nature that there is a "simply astonishing" lock-step link between phytoplankton productivity and ocean surface temperatures. Cooler temperatures encourage convection that brings nutrients up from below into the sunlit zone. Then the tiny plants thrive. Warmer surface water cuts back that convection. Phytoplankton, starved for nutrients, are less productive.
This finding gives new insight into the effect of climate change on the web of ocean life. "The evidence is pretty clear that the Earth's climate is changing dramatically," notes research team member Gene Carl Feldman with NASA's Goddard Space Flight Center in Greenbelt, Md.
