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The Boston Globe

World

A stern warning on global warming

Warns of nearing key carbon level; says main cause is human activity

STOCKHOLM — The world’s top climate scientists on Friday formally embraced an upper limit on greenhouse gases for the first time, establishing a target level at which humanity must stop spewing the gases into the atmosphere or face irreversible climatic changes. They warned that the target is likely to be exceeded in a matter of decades unless steps are taken soon to reduce emissions.

Unveiling the latest United Nations assessment of climate science, the experts cited a litany of changes already underway, warned that they would probably accelerate and expressed virtual certainty that human activity is the main cause.

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