Climate 'threat' to US water

The Alaskan permafrost is set to retreat further

By environment correspondent Alex Kirby

Climate change during this century could seriously affect water resources in the US, a report warns.

It says areas including Cape Cod, Long Island and the central coast of California may be affected.

It says there has already been "substantial" thawing of the Alaskan permafrost and "unprecedented" glacier melting.

And it expects the permafrost to retreat 500 km (310 miles) northwards in the next 50 years.

The report, Water: The Potential Consequences of Climate Variability and Change, is the work of the National Water Assessment Group (Nwag).

Flexible approach

Nwag includes representatives from government, corporate and non-governmental sectors.

The lead author, Peter Gleick, president of the Pacific Institute, said some changes were inevitable.

Snowfall has been decreasing

"Sole reliance on traditional management responses is a mistake," he said.

"Water managers need to integrate possible climate change impacts into their planning processes and to build flexibility into the system to maximise our ability to respond to changing conditions."

The report says the temperature in the US has risen by about two-thirds of a degree Celsius over the last century, with 1998 the warmest year recorded.

It says the evidence that humans are changing the water cycle of the US is "increasingly compelling", and offers several examples:

• the start of the thawing of the Alaskan permafrost
• a mean sea level rise of between 10 and 20 cm since the 1890s
• mountain glaciers melting "at rates unprecedented in recorded history"
• a significant decline since the 1950s of Arctic ice thickness levels, "much larger than would be expected from natural climate variability"
• vegetation blooming earlier in the spring and summer and continuing to photosynthesise longer in the autumn
• an annual mean decrease in snow cover of about 10% over north America since 1988.

While they note that many uncertainties remain and are likely to persist, the authors say it is "vital that these should not be used to delay or avoid taking certain kinds of action now".

They foresee further changes ahead - increased global average rainfall, for instance, more frequent floods and droughts in certain areas of the US as temperatures increase by a projected three to six degrees C by 2100 and salt water penetrating further inland as glaciers melt and sea levels rise.

Moving northwards

And they believe that it is not only species distributions that will shift northwards in response to rising temperatures.

"The southern boundary of continuous permafrost is projected to shift north by 500 km (310 miles) over the next 50 years due to warming projected by global climate models", they write.

"A five degrees C warming in Alaska would eventually melt all of the subarctic permafrost there, which would affect more wetland area than is currently found in the rest of the US".

The authors are concerned about the possibility that rising sea levels will let sea water into groundwater aquifers and freshwater coastal systems.

Areas at greatest risk, they say, include Hawaii, Nantucket, Martha's Vineyard, Long Island, New York, and central coastal California.

Sceptical view

They call for research on the implications of climate change for international water law, US treaties and agreements with Mexico and Canada, and international trade in water.

Some scientists still dispute that human-induced global warming is happening. They argue that the computer models on which future scenarios of climate change are based, and which are driving the greenhouse debate, are deeply flawed.

They also dispute the view that the Earth is currently experiencing a rapid warming. They say that satellite data and balloon studies suggest no such warming is taking place.