The effects of climate change will be “severe, pervasive and irreversible” within the next few decades if countries burn more than just one-quarter of the fossil fuel reserves already found, according to a major new U.N. draft report. Already, failure to heed earlier scientific advice regarding fossil fuel emissions have “made large-scale climatic shifts inevitable,” but a significant reduction of emissions now could still slow these changes, and buy the human race some time to adapt to an altered world.

The draft report, which compiles hundreds of earlier papers, was leaked ahead of its planned November release date and obtained by the New York Times. It warns that companies and governments have “identified reserves of these [fossil] fuels at least four times larger than could safely be burned if global warming is to be kept to a tolerable level." In short, 75 percent of the fossil fuels must remain in the ground to forestall devastating impacts like major sea level rise, severe drought, and mass extinction of plant and animal species. The report, however, notes that notorious political foot-dragging on the issue, as well as the economic consequences of drastically curbing the fossil fuel industry, give little hope for the stop-gap recommendation to actually be observed.  

“The new report found that it was still technically possible to limit global warming to an internationally agreed upper bound of 3.6 degrees Fahrenheit, or 2 degrees Celsius, above the preindustrial level. But continued political delays for another decade or two will make that unachievable without severe economic disruption,” the Times writes. Political inaction has become a hallmark of this issue after decades of international emissions negotiations. Prior summits have ended with weak agreements or little more than an "outline."  Next month, world leaders will gather in New York for a summit intended to begin negotiations for a global agreement on emissions to be completed in 2015.

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Meanwhile, the world may already be approaching a temperature at which complete loss of the enormous ice sheet that covers Greenland would “become inevitable,” the Times reports. The report explains that the actual melting would then take several hundred years to complete, but at a certain temperature would become unstoppable. The resulting sea level rise could total as much as 23 feet, wiping out many of the world’s major cities.

“Many aspects of climate change and associated impacts will continue for centuries, even if anthropogenic emissions of greenhouse gases cease,” the report finds.

To date, the Earth has warmed by about 1.5 degrees Fahrenheit above pre-industrial levels, an increase that has already prompted climate-related changes like a drop in global grain production by several percentage points, according to the Times. A business-as-usual approach to the growth of the fossil fuel industry could result in warming of in excess of 8 degrees Fahrenheit in the "coming decades." It is hard to imagine the infrastructural shifts that would be needed to adapt the global population to such a changed world, but the "coming decades" certainly do not afford us enough time to implement them.