The debate on global warming is over

That's the ultimate message from the report released in Paris today by the Intergovernmental Panel on Climate Change (IPCC), the U.N. body of leading researchers charged with analyzing climate science and producing the final word on what is happening — and will happen — to our planet. IPCC scientists now say that it is "very likely" that global warming is chiefly driven by the buildup of carbon dioxide (CO2) and other greenhouse gases caused by human activity, and that dangerous levels of warming and sea rise are on the way.
Those two words — the product of 2,500 scientists, 130 nations and 6 years of work — translates into a certainty of over 90%, up from the 66 to 90% chance the panel reported in its last major climate change assessment in 2001. That might not seem like a big difference, but in science, especially in a field as rapidly developing as climate studies, 90% is as good as it gets. The new report effectively completes a scientific revolution that began at the end of the 19th century, when a Swedish geochemist named Svante Arrhenius first proposed that CO2 released into the atmosphere by burning fossil fuels could change the planet's climate. "The message of this report is that the time for sitting on the fence is finished," says Robert Watson, chief scientist at the World Bank and a former chair of the IPCC. "Now is the time for action. Time