Panel’s Warning on Climate Risk: Worst Is Yet to Come

Climate change is already having sweeping effects on every continent and throughout the world’s oceans, scientists reported on Monday, and they warned that the problem was likely to grow substantially worse unless greenhouse emissions are brought under control.

The report by the Intergovernmental Panel on Climate Change, a United Nations group that periodically summarizes climate science, concluded that ice caps are melting, sea ice in the Arctic is collapsing, water supplies are coming under stress, heat waves and heavy rains are intensifying, coral reefs are dying, and fish and many other creatures are migrating toward the poles or in some cases going extinct.

The oceans are rising at a pace that threatens coastal communities and are becoming more acidic as they absorb some of the carbon dioxide given off by cars and power plants, which is killing some creatures or stunting their growth, the report found.

Organic matter frozen in Arctic soils since before civilization began is now melting, allowing it to decay into greenhouse gases that will cause further warming, the scientists said. And the worst is yet to come, the scientists said in the second of three reports that are expected to carry considerable weight next year as nations try to agree on a new global climate treaty.

In particular, the report emphasized that the world’s food supply is at considerable risk — a threat that could have serious consequences for the poorest nations.

“Nobody on this planet is going to be untouched by the impacts of climate change,” Rajendra K. Pachauri, chairman of the intergovernmental panel, said at a news conference here on Monday presenting the report.

The report was among the most sobering yet issued by the scientific panel. The group, along with Al Gore, was awarded the Nobel Peace Prize in 2007 for its efforts to clarify the risks of climate change. The report is the final work of several hundred authors; details from the drafts of this and of the last report in the series, which will be released in Berlin in April

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