Nov 22, 2021 - Energy & Environment

Study casts doubt on climate emissions pledge estimates

Flooding in British Columbia after a major storm struck the region.
In an aerial view, floodwaters surround homes and farms on Nov. 20 in Abbotsford, British Columbia. Photo: Justin Sullivan/Getty Images

A new analysis casts doubt on whether scientists can precisely estimate how much nations' combined emissions-cutting pledges will stem global warming, instead showing a wide range of potential outcomes.

Why it matters: World leaders need to know if emissions targets currently on the table would meet the Paris Agreement's temperature goals or if more stringent commitments are needed. The new study shows they may be placing too much faith in temperature projections.

  • During COP26 in Glasgow, analyses showed that a business-as-usual course of greenhouse gas emissions would yield about 2.7°C (nearly 4.9°F) of global warming compared to preindustrial levels in 2100.
  • Quick analyses released during the talks showed that all of the COP26 emissions pledges, including action on methane emissions, could bring that down to below 2°C. But the new study casts doubt on the accuracy of these figures.

Threat level: For the new study, published in the journal Nature Climate Change, scientists used seven different computer models to simulate how future emissions may play out through 2030, 2050 and 2100. It shows the dangers of focusing too much on specific global warming forecasts.

  • This is because of the uncertainties involved in projecting future emissions and economic growth, along with model uncertainties and other factors.
  • The world has already warmed by 1.1°C (nearly 2°F), bringing a slew of devastating extreme weather events.

Context: At COP26, the International Energy Agency offered up a projected warming figure of 1.8°C (3.2°F), provided every voluntary emissions pledge (known as Nationally Determined Contributions, or NDCs) would be met on time and taking into account pledges to cut emissions of methane, a powerful greenhouse gas, as well as net-zero commitments for 2050.

  • Other reports, such as data from the nonprofit Climate Action Tracker, found that the world is now on a path to warm by 2.4°C (4.32°F) when looking only at 2030 targets.
  • "Even with all new Glasgow pledges for 2030, we will emit roughly twice as much in 2030 as required for 1.5°," the Tracker's analysis stated.
  • Such warming would be above the Paris Agreement's target of keeping warming to "well below" 2°C, with the stretch goal of limiting it to 1.5°C.

What's new: The new study began a year ago and focused on how large a range of warming the models projected, in order to get a better idea of the uncertainties involved.

  • The models showed that current policies, which would not involve stringent emissions cuts, would lead to between 2.3°–2.9°C (4.1°–5.2°F) of warming by 2100.
  • When including the NDCs, that range would come down somewhat to 2.2°–2.7°C (3.9°–4.9°F) above preindustrial levels by 2100.

Yes, but: When accounting for uncertainties in how the climate will respond to additional amounts of greenhouse gases, the study shows a wider range of potential outcomes.

  • Global warming could reach as high as 3.8°C (6.84°F) above preindustrial levels, or as low as 1.7°C (3.1°F), when such uncertainties are taken into account.

What they're saying: "Really we are quite uncertain about where current policies and NDCs take us, contrary to a lot of the media and communication during COP26," study co-author Glen Peters of the CICERO Center for International Climate Research in Norway, told Axios in an email.

  • "This is important in a policy context, as ambitious climate goals could be further out of reach than often believed."
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