US PRESIDENT George Bush's top science advisers have issued a report that, for the first time, endorses what most scientific experts have long argued: that greenhouse gases from fossil fuel combustion "are very likely the single largest cause" of the earth's warming.
The Bush Administration had long resisted a Congressional mandate, the 1990 Global Change Research Act, requiring the White House to report every four years on global warming and other environmental forces.
A US District Court last August ordered Mr Bush to comply with a 2004 deadline for an updated report, after a lawsuit by the Centre for Biological Diversity and other environmental groups.
Sharon Hays, deputy director of the White House Office of Science and Technology Policy, said the report did not represent a changed assessment, but "a rolling-up of a whole bunch of reports on the science, showing that climate change is primarily caused by human activity of the last 50 years".
The Administration had earlier issued reports on the effect of climate change on transportation, agriculture and human health. But environmentalists celebrated what they saw as a long-overdue admission from an Administration that has been reluctant to join global efforts to curb greenhouse gases, such as the 1997 Kyoto Protocol.
"This report represents a stark shift in what the Administration has been saying since 2001," said Philip Clapp, deputy managing director of the Pew Environment Group. "For the first time, it has had to admit that global warming is already having clear impacts in the United States, and the impacts are going to get worse even with the most aggressive action to cut emissions."
The report by the National Science and Technology Council and the US Climate Change Science Program asserted that natural causes alone could not explain recent extremes of heat and cold, warming seas and an increase in the frequency and intensity of hurricanes. It also shows that regions of North America could warm faster over the next few decades than the global average.
The warming climate also will accelerate the spread of diseases carried by water, food and insects.
The few positive effects of climate shifts are outweighed by negatives. For example, warming and higher levels of carbon dioxide will speed up growth of forests and certain crops, but also increase insect outbreaks and spark more wildfires.
Warmer, less-snowy winters would decrease winter road maintenance cost, but increased coastal and river-related flooding and landslides were likely to cause more serious problems. Heat spells, the report said, "could cause railroad tracks to buckle or kink and could affect roads through softening and traffic-related rutting".
Industry representatives greeted the report with a shrug. Jim Owen, spokesman for the Edison Electric Institute, said the power industry "abandoned the science debate years ago. It's universally recognised in our industry that climate change is very real."
LOS ANGELES TIMES