Hot topic gets warm support

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Global warming is getting hotter both politically and climatically. Key skeptics of global warming among American evangelical Christians have made a 180-degree turn. They now call for immediate action to curb emissions of the heat-trapping carbon dioxide gas that drives climate warming.

Last month, 86 evangelical leaders issued a statement that frames the climate-change debate as a moral issue. Titled "Climate Change: an Evangelical Call for Action," it states that "human-induced climate change is real." It adds that global warming will have "significant" consequences that "will hit the poor hardest." It concludes that "Christian moral convictions demand our response to the climate change problem."

The statement urges individuals and their churches to act locally and nationally to implement - and to urge the national government to implement - measures to reduce human-driven climate change. Theirs will be voices friendly to the Bush administration, urging that administration to rethink its reluctance to take serious action to reduce CO2 emissions.

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At the same time, another friendly voice urging such action is becoming more insistent. A few weeks ago, British Prime Minister Tony Blair told Parliament that Britain is now in a position to meet its CO2 emission reduction targets mandated by the Kyoto climate change treaty. He also promised to work harder to persuade "India, China, and the United States" of the need to act aggressively to limit global warming.

The case for reducing CO2 emissions has also become stronger as climate trends become clearer. Comprehensive measurements of ice mass loss from Antarctica and Greenland highlight the climate change threat. They also indicate that previous computer simulations - hampered by the inclusion of assumptions about change when relevant data are lacking - have underestimated the speed with which the ice is melting and raising sea level.

The ice reservoirs of Antarctica and Greenland are the largest on Earth. If they melt entirely, they would raise sea level several meters. Knowing whether there is a net loss in these ice reservoirs today and how fast any such loss is proceeding has been a major uncertainty. But recent measurements are clearing this up.

The first such study of Antarctica was published in Science earlier this month. Scientists had thought the continent's total ice mass was more or less stable. The new study shows this isn't so. A US-German satellite mission called GRACE that was launched in 2002 uses a pair of satellites to measure Earth's gravity field in minute detail. It is able to determine the total mass of Antarctic ice by its effect on that gravity field. The measurements show that every year Antarctica is losing more ice into the sea than it gains from snowfall.

Last month, NASA reported that Greenland continues to gain more ice from snowfall than it loses annually. But its ice loss to the sea is accelerating. It doubled between 1996 and 2005. Another recent NASA study concluded that, if the trend continues, "the Greenland ice sheet could be facing an irreversible decline by the end of the century."

These changes are much larger than have been predicted by computer simulations. The results show that uncertainties in climate-change simulations could understate those changes as much as they might overstate them.

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