How high would the world’s average temperature rise if we burned all available fossil fuels? Really, really hot.
Michael Greenstone, a professor of economics at the University of Chicago, calculated that the Earth’s atmosphere would be 16.2˚ F warmer than at the start of the Industrial Revolution. To put that number in context, the planet has warmed just 1.7˚ F since then.
Greenstone was relatively conservative in his estimates, too, assuming that we wouldn’t develop more effective ways of extracting coal, oil, or gas from difficult to access sources. Using a carbon-climate response model published in the journal Nature in 2009, he calculated how much the planet would warm if we burned every bit last fossil fuel available with today’s drilling and mining technology, even those deposits which are technically accessible but prohibitively expensive to exploit. If we grow more adept at fracking or figure out how to exploit other sources, such as methane hydrates trapped on the ocean floor, the estimate could rise significantly.
Greenstone breaks it down for the New York Times’ Upshot:
Since the industrial revolution, fossil fuels have warmed the planet by about 1.7 degrees. We are already experiencing the consequences of this warming. In recent weeks, we have learned that the world had its warmest winter on record and that Arctic sea ice hit a new low, even as intense storms continue to inflict harm on communities globally.
Next, look at fossil fuel reserves, the deposits we know to be recoverable under today’s prices and technology. That is, they are inexpensive to access. If we were to use all of this coal, natural gas and petroleum, the planet would warm by an additional 2.8 degrees. Add the heat from those reserves to the 1.7 degrees from what has already been emitted, and you get a world that is 4.5 degrees warmer since the industrial revolution; this is beyond scientists’ recommended 3.6-degree threshold.
The next set of fossil fuels in line is referred to as resources, rather than reserves. The difference is that they are recoverable with today’s technology, but not at current prices. There is 3.1 degrees’ worth of warming if the oil and natural gas in this category are utilized, which would lead to a total increase in global temperatures of 7.6 degrees.
This warming does not even consider our coal resources. A middle-of-the-road estimate of the coal that qualifies as resources indicates that its use would lead to an additional increase of 8.6 degrees. Thus, the use of all reserves and resources would lead to a total increase of 16.2 degrees. Today’s climate and planet would very likely be unrecognizable.
The last time the Earth’s temperature reached those levels was when it was cooling off after the Paleocene-Eocene Thermal Maximum, a sweltering period about 56 million years ago. Back then, volcanoes initiated a feedback cycle that pumped the equivalent of 2.2 billion tons of carbon into the atmosphere per year. Average global temperature peaked at a whopping 25˚ F higher than the present. Today, we’re releasing 35.5 billion tons from energy consumption alone.