How Hot Is Too Hot?

4°Celsisus (about 7.2°Fahrenheit), that's how hot. Thus sayeth the World Bank in its new report, Turn Down the Heat: Why a 4°C Warmer World Must Be Avoided. Yet that's precisely where we're headed:

Despite the global community’s best intentions to keep global warming below a 2°C increase above pre-industrial climate, higher levels of warming are increasingly likely. Scientists agree that countries’ current United Nations Framework Convention on Climate Change emission pledges and commitments would most likely result in 3.5 to 4°C warming. And the longer those pledges remain unmet, the more likely a 4°C world becomes.

The implications of a 4°C world were teased out for the Bank by the Potsdam Institute for Climate Impact Research and Climate Analytics. They make for very dreary reading: sea-level rise of .5 to 1 meters; increase in tropical cyclone intensity; extreme heat waves like that which struck Russia in 2010 becoming the norm; mass migrations of peoples as islands sink and entire regions become uninhabitable.

In this new high-temperature climate regime, the coolest months are likely to be substantially warmer than the warmest months at the end of the 20th century.

"It is my hope that this report shocks us into action," says World Bank President Jim Yong Kim in his foreword. "A 4°C world can, and must, be avoided. . . . The solutions don't lie only in climate finance or climate projects. The solutions lie in effective risk management and ensuring all our work, all our thinking, is designed with the threat of a 4°C world in mind."

PAUL RAUBER is a senior editor at Sierra. He is the author, with Carl Pope, of the happily outdated Strategic Ignorance: Why the Bush Administration Is Recklessly Destroying a Century of Environmental Progress. Otherwise he is a cyclist, cook, and father of two. Follow him on Twitter @paulrauber.