The world’s top climate scientists on Friday unveiled their much-anticipated assessment of global warming and the conclusion couldn’t be more definitive: It is "extremely likely" that human activity is the "dominant cause of climate change observed since the 1950s."
The Intergovernmental Panel on Climate Change (IPCC) said they are 95 percent convinced that global warming is both occurring and man-made. This is an increase from the United Nations-sponsored panel’s last assessment, issued in 2007, when they said with 90 percent certainty that global warming was real and caused by man.
One anecdote that didn’t appear in the report, however, is that the IPCC’s new calculations essentially support the conclusions drawn in Bill McKibben’s now-famous Rolling Stone article from 2012, "Global Warming’s Terrifying New Math."
In that story, the climate hawk and founder of 350.org, posited that there were three key numbers that global policymakers needed to focus on to prevent calamitous climate change.
1) The First Number: 2° Celsius [3.6° Fahrenheit]: This is the temperature rise we need to target if we want to have our best chance of averting multiple catastrophes and amplifying carbon cycle feedbacks.
The IPCC agrees with McKibben, and McKibben got his number from prior IPCC reports: Two degrees is still considered "safe."
2) The Second Number: 565 Gigatons: Scientists estimate that humans can pour roughly 565 more gigatons of carbon…into the atmosphere by midcentury and still have some reasonable hope of staying below two degrees. (‘Reasonable,’ in this case, means four chances in five, or somewhat worse odds than playing Russian roulette with a six-shooter.)”
Here's where the IPCC starts to make the math a little harder. As of 2011, we had emitted roughly 531 billion tons of carbon since the Industrial Revolution, meaning we have already burned through about 53 percent of a targeted one-trillion-ton carbon budget. So we only have 469 billion tons—not 565 billion tons, as McKibben wrote—left to spend in our carbon budget.
The trouble is that we've greatly increased population and industrialization since the start of the Industrial Revolution—it took us 250 years to burn the first half, but at our current rate we'll burn through the second half in the next 30 years.
3) The Third Number: 2,795 Gigatons: “This number is the scariest of all—one that, for the first time, meshes the political and scientific dimensions of our dilemma….The number describes the amount of carbon already contained in the proven coal and oil and gas reserves of the fossil-fuel companies, and the countries (think Venezuela or Kuwait) that act like fossil-fuel companies. In short, it’s the fossil fuel we’re currently planning to burn.
The new consensus from the IPCC puts this number closer to 3,000 gigatons, or 205 more than McKibben projected. Though, to be sure, it's hard to pin down, as new discoveries are made and new technologies are invented.
But what's critical for humanity is the gigatons that we can afford to burn, not what we keep on finding but can't burn. Indeed, every proposed coal mine needs to be evaluated in the same way a lobster dinner does for a person on a budget: 'Can we afford this or will it blow a hole in our budget?'
McKibben had estimated leaving 79.8 percent of the fossil fuels in the ground (565 gigatons divided by 2,795 gigatons)—a daunting challenge of math, policy and politics. The IPCC's new math is even more terrifying: 469 gigatons divided by 3,000 gigatons, or 84.3 percent of the world's fossil fuels need to remain forever untouched.
"In a way, the biggest development since the last IPCC report is the now obvious idea that we have to leave most of the carbon we've found underground," McKibben told TakePart on Friday. "Global warming is a big math problem, and the bottom line is now clearly in focus."
Mary Robinson, president of Ireland from 1990 to 1997, agreed with McKibben, telling The Guardian that governments would have to confront the harsh reality that much of their fossil fuel reserves, and accompanying economic value, would have to be left behind if runaway emissions were not to threaten the climate. "There is a global limit on a safe level of emissions," she said. "That means major fossil fuel reserves must be left in the ground. That has huge implications for economic and social development."
One item left out of the IPCC report: The impact of climate change on human society and planetary ecosystems. That section of the assessment isn’t due for another six months. For now, the math alone paints a terrifying picture.