Climate researchers argue changes will be significant in decades, not centuries

New York Times : A study that stirred controversy among climate scientists when a draft version first circulated last year has now been published in the journal Atmospheric Chemistry and Physics. In the paper, retired NASA climate scientist James Hansen and colleagues argue that the amount of warming set as a goal at the Paris climate talks is enough to cause major climate changes by the end of this century. The researchers reached that conclusion by comparing the modern situation with a period roughly 120 000 years ago, when Earth warmed naturally to a temperature only slightly higher than current levels. In that era most of the polar ice sheets melted and sea levels were 20–30 feet (6.1–9.1 m) higher. Melting of the polar ice sheets, the researchers say, would release a large amount of freshwater that could slow or even stop the ocean’s system of currents that redistribute heat around the planet. As a result, more heat would accumulate in the oceans, accelerating melting, exacerbating the temperature difference between tropical and polar regions, and triggering powerful storms. The paper cites controversial evidence for significant storms in the previous warm period. The slowdown of ocean currents is also not widely accepted by climate researchers. But its inclusion in the paper may result in reexamining the scenario using modern computer simulations that were not available when the theory was proposed more than a decade ago.