Evidence mounts: Warming trend changes climate

Indications of man-made global warming continue to appear. It shows up in the latest study that confirms that the 20th century is the warmest century of the millennium. It is reflected in warmer winters around the Northern Hemisphere.

Meanwhile in the United States, some scientists studying potential consequences of climate change are forming partnerships with public officials, business people, and the public to give their research a practical edge. It's part of a national program to assess what climate change may mean at a local and regional level.

The aim is to include all the stakeholders - "anyone who makes real decisions in the real world," says Cynthia Rosenzweig, an agronomist at the NASA Goddard Space Flight Center in Greenbelt, Md.

It is hard to pin down climate change when research reveals trends that are consistent with man-made global warming but do not prove human guilt definitively. A team of

British and American scientists led by Paul Jones of Britain's University of East Anglia in Norwich, published a thousand years' worth of temperature trends in last month's Reviews of Geophysics. They report that "the warmest years on record all occurred in the 1990s."

The team notes that most of this century's warming occurred from 1925 to 1944 and 1978 to 1997. The minimum average night temperature has risen 0.18 degrees F. per decade. The daytime maximum has risen 0.14 degrees F. All of this is consistent with warming due to the increase of greenhouse gases. But it doesn't reveal how much of the warming would have occurred naturally.

The same is true for the warming of Northern Hemisphere winters. In the June 3 issue of Nature, Drew Shindell at NASA's Goddard Institute for Space Studies in New York, reports a possible link between this warming and the buildup of greenhouse gases. Over the past 30 years, the winter warming has reached levels 10 times higher than the rise in the average global temperature.

Dr. Shindell has matched this weather with changes in Arctic wind patterns, which are themselves linked to accumulating greenhouse gases. He points out that, once again, the research suggests a human influence but does not prove it. Nevertheless, he says: "In our model, we're seeing a very large signal of global warming and it's not a naturally occurring thing."

Dr. Rosenzweig is concerned with preparing New York City's metropolitan region to cope with potential effects of global warming. Her associates include people concerned with transportation, public health, coastal erosion, water supply, and wetlands. Among other effects, they note that sea-level rise already is increasing shoreline erosion. Predictions also indicate it could intrude salt water into the city's freshwater supply.

The Pacific Northwest region provides another example. Environmental engineer Dennis Lettenmaier at the University of Washington in Seattle, reports that the best computer models and data trends indicate that the annual snow line is receding to higher elevations. "That's a lot of water not being stored in the mountains," he says. Resource managers have to plan for alternative storage - reservoirs or dams, which raise other environmental concerns. "It's a serious issue," Professor Lettenmaier says.

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