(CNN) -- It's hot out there. But this time, it's more than idle watercooler talk, according to weather scientists.
At the same time the National Oceanic and Atmospheric Administration's National Climatic Data Center has released a report noting that this spring in the United States has been the warmest since record-keeping began in 1895, a group of scientists has published a paper in the journal Nature warning that the planet is approaching a critical tipping point because of climate and other factors.
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