World can still keep warming below 2 C — if countries keep their climate promises, study says

If nations do all that they've promised to fight climate change, the world can still meet one of two internationally agreed upon goals for limiting warming. But the planet is blowing past the other threshold that scientists say will protect Earth more, a new study finds.

The world is potentially on track to keep global warming at, or a shade below, 2 C (3.6 F) hotter than pre-industrial times, a goal that once seemed out of reach, according to a study published Wednesday in the journal Nature.

That will only happen if countries not only fulfil their specific pledged national targets for curbing carbon emissions by 2030, but also come through on more distant promises of reaching net zero carbon emissions by mid-century, the study says.

This 2 C warmer world still represents what scientists characterize as a profoundly disrupted climate with fiercer storms, higher seas, animal and plant extinctions, disappearing coral, melting ice, and more people dying from heat, smog and infectious disease. It's not the goal that world leaders say they really want: 1.5 C (2.7 F) since pre-industrial times. The world will blast past that more prominent and promoted goal unless dramatic new emissions cuts are promised and achieved this decade and probably within the next three years, study authors said.

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Both goals of 1.5 C and 2 C are part of the 2015 Paris climate pact and the 2021 Glasgow follow-up agreement. The 2-degree goal goes back years earlier.

"For the first time, we can possibly keep warming below the symbolic 2-degree mark with the promises on the table. That assumes of course that the countries follow through on the promises," said study lead author Malte Meinshausen, a University of Melbourne climate scientist.

That's a big if, outside climate scientists and the authors, say. It means political leaders actually doing what they promise

The study "examines only this optimistic scenario. It does not check whether governments are making efforts to implement their long-term targets and whether they are credible," said Niklas Hohne of Germany, a New Climate Institute scientist who analyzes pledges for Climate Action Tracker and wasn't part of this study. "We know that governments are far from implementing their long-term targets."

Hohne's team and others who track pledges have similarly found that limiting warming to 2 C is still possible, as Meinshausen's team has. The difference is that Meinshausen's study is the first to be peer-reviewed and published in a scientific journal.

Sure, the 2-degree world requires countries to do what they promise. But cheaper wind and solar have shown carbon emissions cuts can come faster than thought and some countries will exceed their promised cuts, Meinshausen said. He also said the way climate action works is starting with promises and then policies, so it's not unreasonable to take countries at their word.

Mostly, he said, limiting warming to 2 degrees is still a big improvement compared to just five or 10 years ago, when "everybody laughed like, 'Ha. We'll never see targets on the table that bring us closer to 2 degrees,'" Meinshausen said. "Targets and implemented policies actually can turn the needle on future temperatures. I think that optimism is important for countries to see. Yes, there is hope."

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About 20 per cent to 30 per cent of that hope is due to the Paris climate agreement, but the rest is due to earlier investments by countries that made green energy technologies cheaper than dirty fossil fuels such as coal, oil and natural gas, Meinshausen said.