Global climate is approaching critical tipping points that could lead to loss of all summer sea ice in the Arctic with detrimental effects on indigenous people and wildlife, initiation of ice sheet disintegration in West Antarctica and Greenland with progressive, unstoppable global sea level rise, shifting of climatic zones with extermination of many animal and plant species, melting of most mountain glaciers with loss of freshwater supplies for hundreds of millions of people, and a more intense hydrologic cycle with stronger droughts and forest fires, but also heavier rains and floods, and stronger storms driven by latent heat, including thunderstorms, tornados and tropical storms.

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There is urgent need for actions to stem climate change. The Earth’s climate history and ongoing climate changes show that our climate today is approaching tipping points, which, if passed, could have devastating consequences.

Fundamental knowledge about fossil fuel carbon reservoirs reveals an imperative: coal use must be promptly phased out except where CO2 is captured and sequestered. Yet building of new coal-fired power plants continues unabated.

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This letter should explain that the leaders realized their failure to take these actions would cause our descendants to inherit a planet with a warming ocean, disintegrating ice sheets, rising sea level, increasing climate extremes, and vanishing species, but it would have been too much trouble to make changes to our energy systems and to oppose the business interests who insisted on burning every last bit of fossil fuels. By composing this letter the leaders will at least achieve an accurate view of their place in history.

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More from James Hansen can be found via his home page:  http://www.columbia.edu/~jeh1/