Scientists settle on low end of carbon budget spectrum

Review of research proposes smaller allowance of carbon dioxide emissions to cap warming to safe levels, adding pressure to efforts to cut emissions

Economies must decarbonise rapidly to avert dangerous warming, say scientists (credit: UN)

Economies must decarbonise rapidly to avert dangerous warming, say scientists (credit: UN)

By Alex Pashley

Countries agreed last year to limit global warming to 2C this century and “pursue efforts” to hold it to 1.5C to avoid dangerous climate change. 

Scientists have come up with a range of estimates for the cap on greenhouse gas pollution needed to have a likely chance of avoiding that threshold. It’s known as the “carbon budget”.

A review of the evidence on Wednesday published in journal Nature Climate Change recommended dismissing the more generous allowances.

From 2015 onwards, there is only room for another 590-1,240 gigatons of carbon dioxide equivalent, it found. That includes other gases like ozone, methane, and nitrogen dioxide.

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Some studies have put the upper limit as high as 2,390 GtCO2. But the report authors said those figures were not robust as they did not account for all greenhouse gases or had other methodological limitations.

The findings add urgency to international effort to curb global emissions, which stood at 40Gt CO2e in 2014 and at current rates will eat up the budget within 15-30 years. It requires overhauling centuries of fossil fuel-based development and the swift adoption of clean energy technologies.

“We have figured out this budget is at the low end of what studies indicated before, and if we don’t start reducing our emissions immediately, we will blow it in a few decades,” said Joeri Rogelj at the Vienna-based International Institute for Applied Systems Analysis, who led the study.

“[M]any different factors can lead to carbon budgets that are either slightly smaller or slightly larger. We wanted to understand these differences, and provide clarity on the issue for policymakers and the public.”

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