Rising temperatures forecast to change American life

WASHINGTON - Alpine meadows will disappear, along with many coastal wetlands and barrier islands. Cities will be hotter and more humid. Ski runs will be scarcer, the demand for air conditioners will increase, and scientists will have to combat a likely resurgence in insect-borne diseases such as malaria.

This is the weather forecast for the late 21st century, when average U.S. temperatures will have risen by 5 degrees to 10 degrees.

Assailed by some critics as too pessimistic and little more than guess work, that assessment is of a country coping with global warming.

Four years in the making, the report reflects the most ambitious attempt to gauge the impact of climate change on America.

A dozen government agencies and hundreds of scientists, in and out of government, worked on ''Climate Change in America.'' It will be released next week and later presented to Congress, which asked for the assessment a decade ago.

The Associated Press obtained a late draft of the report's overview summary.

''Based on the best available information, most Americans will experience significant impacts'' from Earth's warming, the report concludes. Among the findings:

-Entire ecosystems may shift northward as temperatures increase.

-The Alpine meadows of the Rocky Mountains likely will disappear.

-Forests in the Southeast may break into ''a mosaic of forests, savannas and grasslands'' and sugar maples could disappear from Northeastern forests.

-Ocean levels will rise, causing wetlands, marshes and barrier islands to disappear or - when the geography allows - be force inland.

-The Great Lakes are predicted to decline because of increased evaporation causing yet different problems.

-Some coastal cities, faced with sea level rise and more frequent storm surges, may have to redesign and adapt water, sewer and transportation systems. The study does not attempt to put a cost to such improvements.

Some critics have charged it paints too dismal a picture and plays down potential benefits of warming - increased crop yields and warmer winters that may make life more pleasant in some areas, for example.

The document acknowledges ''a complex mix of positive and negative impacts'' if, as most climate scientists predict, pollution in the atmosphere raises temperatures worldwide by an average of 4 degrees to 9 degrees over the next 100 years.

An early draft of the overview summary was attacked in December as having ''an extreme, alarmist tone'' on predicting impact on human health. The summary has been revised with more emphasis on the uncertainties of predicting health impacts.

Nevertheless, the study says higher temperatures and increased rainfall likely will exacerbate air pollution, saddle large cities with more frequent and severe heat waves, and lead to the spread of waterborne or insect-carrying diseases including malaria in the Southeast.

But society can lessen these threats and the ''future vulnerability of the U.S. population to the heath impacts of climate change depends on our capacity to adapt,'' according to the late draft.

In much of America, winter may disappear, limiting outdoor activities such as skiing.

Warmer weather will reduce the mountain snowpack, curtailing the summer runoff that feeds irrigation across much of the West and complicating water management.

But more rain is predicted for the arid Southwest. That could bring new vegetation - and more flash floods - to desert lands. Tree, fish and animal species will migrate northward everywhere.

In the Pacific Northwest, the salmon may shift north to Alaska, replaced by warmer water species. In Alaska the rising temperature is expected to cause further thawing of permafrost, damaging roads and buildings.

But warming also bring positive results, the study says.

Trees will grow faster and the amount of timber in America's forests - especially hardwoods - will increase steadily through the century.

Farmers will be able to grow more crops, although both in agriculture and forestry, there could be increased threats from pests and fire.