End is Near! ‘We may have even less time to stop global warming than we thought’

By: - Climate DepotJuly 30, 2017 11:56 AM

 July 24

A world map shows climate anomalies during the 2015 World Climate Change Conference near Paris. (Stephane Mahe/Reuters)

At least since 2013, one of the biggest concerns in the climate change debate has been the so-called carbon budget — a fixed limit to the volume of carbon dioxide emissions that we can put into the atmosphere before irrevocably committing to a considerably hotter planet.

As of 2011, that budget was about 1,000 billion tons of carbon dioxide before the planet is likely to careen past a 2 degrees Celsius (3.6 degrees Fahrenheit) rise in temperatures, which is above what is believed to be the Earth’s temperature before industrialization. The budget shrinks by about 41 billion tons a year, more recently put at about 600 billion tons (or 15 years of emissions) by a group of scientists and climate policy wonks.

But now, a team of prominent climate scientists say the budget is probably even narrower. The problem is how you define “preindustrial,” or when you consider human-caused perturbations of the atmosphere to have begun. Many analyses have taken the late 19th century as the starting point, but the new study in Nature Climate Change suggests significant human influence was afoot by at least 1750, and may have contributed as much as one-fifth of a degree Celsius of warming (0.36 degrees Fahrenheit) before the late 1800s.

“Frankly, 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 2 degrees Celsius,” said Pennsylvania State University’s Michael Mann, one of the study’s authors. He completed the research with scientists from the universities of Edinburgh and Reading in the United Kingdom.

Defining what counts as “preindustrial” can be a bit of a moving target in climate research, but when the United Nations’ Intergovernmental Panel on Climate Change outlined the carbon budget in 2013, the group said that it was analyzing warming that had occurred “since the period 1861—1880.” But if the world had already warmed by a few slivers of a degree before then, that shrinks the carbon budget by “as much as 40 % when earlier than nineteenth-century climates are considered as a baseline,” notes the new paper.