'Worst-case' climate predictions are 'no longer plausible', study suggests

‘Worst-case’ climate change scenarios with up to 4ºC or 5ºC of warming are no longer possible, a study has suggested.

Researchers at the University of Colorado at Boulder say that such scenarios are based on outdated data from 15 years ago and are no longer likely to happen.

The study also found that the goal of the Paris Climate Agreement to limit warming to 2C is still within reach.

Lead author Roger Pielke Jr, professor of environmental studies at CU Boulder, said: "This is cautiously optimistic good news with respect to where the world is today, compared to where we thought we might be.

"The 2ºC target from Paris remains within reach."

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The most commonly used scenarios, called the Representative Concentration Pathways (RCPs), were developed by the International Panel on Climate Change (IPCC) starting in 2005.

The Shared Socioeconomic Pathways (SSPs) that followed, starting in 2010, were meant as an update. Together, the two sets of scenarios inform the IPCC's fifth and forthcoming sixth assessment reports.

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For their study, Pielke Jr and his co-authors started with a total of 1,311 climate scenarios used by the IPCC, the UN climate body.

Pielke and colleagues compared the scenarios to the projected 2005-2050 fossil fuel and industry carbon dioxide emissions growth rates most consistent with real-life observations from 2005-2020, and International Energy Agency projections to 2050.

The number of scenarios which most closely matched up to data from the past 15 years and subsequent emissions projections ranged from less than 100 to almost 500.

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These scenarios represent what futures are plausible if current trends continue and countries adopt the climate policies they have already announced to reduce carbon emissions.

The analysis joins a growing consensus of independent groups around the world whose work finds that the most extreme climate scenarios are unlikely to occur this century, and mid-range scenarios are more likely.

A report from the IPCC Sixth Assessment Report (AR6) released in 2021 also notes that the likelihood of high emissions scenarios is considered low.

The researchers say that the worst-case scenarios are less plausible because they were developed more than a decade ago.

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Renewable energy has become more affordable and, thus, more common faster than expected, said Matthew Burgess, co-author and fellow in the Cooperative Institute for Research in Environmental Sciences (CIRES) at CU Boulder.

"It's hard to overstate how much the [climate] research has focused on 4ºC and 5ºC scenarios. And those are looking less and less plausible by the year," said Burgess.

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Climate scenarios also tend to overestimate economic growth, especially in poorer countries, according to Burgess, assistant professor of environmental studies.

Relying on not only outdated scenarios, but scenarios which are no longer plausible, for research and policy has big implications for how we think about, act and spend money on climate change issues, the authors said.

Pielke said: "There's a need for these scenarios to be updated more frequently. Researchers may be using a 2005 scenario, but we need a 2022 perspective.

"You're going to have better policies if you have a more accurate understanding of the problem, whatever the political implications are for one side or the other."

The authors stress that 2ºC of warming will still take a dramatic toll on the planet, and this is no time for complacency.

"We're getting close to our 2ºC target, but we definitely have a lot more work to do if we're going to get to 1.5ºC," said Burgess.