The already limited carbon budget available if countries intend to get climate change under control is even narrower than previously thought, according to a new paper in the journal Nature Climate Change that factors in greenhouse gas emissions in the first century of the Industrial Age.
Most climate calculations make the tacit assumption that significant greenhouse gas emissions began sometime after 1860. By then, though, the Industrial Age had actually been hard at work for more than a century. The study by British and American scientists, including Pennsylvania State University’s Michael Mann, analyzed fossil fuel emissions from the time the Industrial Revolution actually got under way around 1750, and 1860, when most emissions inventories begin.
That calculation leads a global carbon budget—the additional volume of emissions that can still be released to the atmosphere without triggering catastrophic climate change—as much as 40% smaller than previously believed.
That budget was thought to be roughly 1,000 billion tons of carbon dioxide or equivalent as of 2011. With earlier industrial emissions factored in, however, that number falls to about 600 billion tons—roughly 15 years’ worth at current emission rates.
One implication is that the human economy will hit its “safe” limit for carbon emissions 15 years sooner than previously anticipated. The prognosis is also grim for the Paris climate agreement’s long-term target of containing warming to 1.5ºC above pre-industrial averages. The new calculation, said Mann, “sort of takes 1.5ºC off the table in the absence of active carbon removal.”
For that matter, Mann added, “this study does indicate that it may be more of an uphill battle than we previously thought in order to stabilize warming below the commonly-defined dangerous limit of 2ºC.”
That limit is open to question, too, noted Reto Knutti, a climate expert with Swiss technical university ETH Zurich. “There is no magic, hard threshold that separates ‘safe’ from ‘dangerous,’” he told the Post, noting that that degree of warming might be tolerable for some countries but catastrophic for others.
Adjusting the start date of emission inventories, Knutti points out, “is just as much a political problem: If countries at some point are made responsible not just for their current but also for their past emissions, then it matters when we start the historical blame game.”
Mann, often a lightning rod for climate deniers, published other research earlier this year supporting findings that climate change is altering the northern hemispheric jet stream, allowing weather patterns like droughts, heat waves, and heavy rain to stall in place for longer.
