More than 8 million health-related deaths worldwide could be avoided through 2040 if nations strengthen their commitments to meeting the Paris Agreement, says a new study. And a separate paper shows that those existing targets are dramatically insufficient, so reductions will need to happen much faster than the current pace if nations are to confidently pursue limiting global warming to 2 degrees Celsius.

Published by two independent groups of scientists on Tuesday, both papers emphasize the high stakes of climate change and the need for quick and large-scale action to avoid its worst damages.

In 2016, 194 countries signed the Paris Agreement and agreed to cap global warming to within 1.5 to 2 degrees Celsius above pre-industrial levels by reducing the planet-heating greenhouse gases they emit. Their first round of self-determined goals — known as nationally determined contributions, or NDCs — has been widely deemed insufficient, and many of the targets are currently undergoing revisions as required by the agreement.

In a paper published in The Lancet Planetary Health, U.K., U.S. and Austrian researchers analyzed how many lives would be saved from issues related to air pollution, diet and physical activity if the Paris Agreement's goals were met. Climate change is “the biggest global health threat of the 21st century,” according to Alice McGushin, a medical doctor and a co-author of the study.

She and her colleagues modeled nine large countries that represent about half of the world’s population and 70% of its greenhouse gas emissions: China, India, the U.S., Indonesia, Brazil, Nigeria, Germany, the U.K. and South Africa. Only India’s NDC was “2 degrees Celsius-compatible,” according to the Climate Action Tracker; the U.S. planned contribution earned the label “critically insufficient,” while Nigeria’s was not rated.

The team found that compared with their initial NDCs, the nations would collectively avoid 8.2 million deaths by beefing up their commitments to meet the Paris Agreement's 2-degree target — about 5.9 million related to diet, 1.2 million related to air pollution and 1.1 million from physical activity.

Another 2 million lives could be saved if the Paris Agreement were accompanied by health-centered policies related to diet, physical activity and transportation, according to the study. This scenario included additional limits on air pollution, and imagined three-quarters of each country’s population walking or cycling for travel and 50% switching to vegan diets while slashing food waste.

These potentially saved lives do not include deaths expected from other effects of unmitigated climate change such as heat waves, extreme weather and food scarcity. But according to McGushin, policies that encourage healthier diets and more active lifestyles would have nearly immediate effects.

“The benefits are close to instant, only seen within the next few years, whereas of course with climate change, the impacts are going to slowly increase over the following century,” said McGushin, who is the program manager at the Lancet Countdown on Health and Climate Change, a collaboration between the U.K. medical journal and 35 research institutions.

Similar analyses have not been conducted in the other countries not examined in the study, but because many struggle with problems of air pollution, obesity and diets, they would substantially benefit from similar responses, she said.

At a time when many countries are updating their NDCs, McGushin considers her research as a good opportunity to engage governments with the Paris Agreement and its public-health benefits.

“There is evidence that health, and particularly looking at health opportunities of tackling climate change, is a great motivator,” McGushin said. “It actually provides public and political incentive to do more.”

And more needs to be done to stop the world from warming by more than 2 degrees Celsius, according to a different study published the same day in Communications Earth & Environment. 

A pair of statisticians from the University of Washington found that for a 50% chance of keeping warming under that limit, carbon dioxide emissions would need to fall by 1.8% each year — 80% faster than the 1% per year that the world’s current NDCs require.

The change required for each country to create the 50-50 odds depends on each nation's preexisting plan as well as its progress so far. The U.S., which is rejoining the Paris accord under President Joe Biden after his predecessor Donald Trump withdrew, would need to increase its 2025 emissions goal by about 38%, for example, while South Korea would require a 136% increase from its 2030 goal, according to the researchers’ statistical modeling.

Reductions would need to be even more aggressive for a 90% chance of limiting warming to 2 degrees Celsius, with a fourfold increase in the annual decline of carbon emissions. The study also found that to have even a 50% chance of keeping warming under 1.5 degrees Celsius, which is the Paris Agreement's stretch goal, an eightfold increase would be required.

Carbon dioxide emissions fell about 1.3% in 2019 as coal use continued to decrease, and they are expected to have declined by a record but likely temporary 7% in 2020 due to the COVID-19 pandemic.

Adrian Raftery, a professor of statistics and sociology at Washington and the paper’s lead author, noted that the world has already warmed 1.1 degrees Celsius from preindustrial levels and that immediately stopping all emissions today would still lead to temperatures rising 1.3 degrees. Reaching the goal of 1.5 degrees Celsius may require a change too challenging to be considered feasible without a unanimous effort to change our ways of life, he said.

“You've got a goal that realistically is so difficult to achieve that people can feel kind of helpless,” Raftery said. “Whereas the kind of things that need to be done to get to two degrees, they're doable. They're hard, but they're doable.”

Much of the world is not on pace to meet even their insufficient NDCs, according to the paper — it gives China and the U.S. a 16% and 2% chance, respectively — let alone the higher standards that would ensure a decent probability of keeping warming under 2 or 1.5 degrees Celsius.

The paper follows up a 2017 publication from Raftery and other researchers that concluded there is just a 5% chance of warming not exceeding 2 degrees Celsius at the current pace. The figure held true in the latest study after adding five more years of emissions data.

Both studies made use of probabilistic modeling Raftery first developed for the United Nations’ population projections. 

The Washington model can be used as a forecast because it calculates the likelihood of each outcome, unlike the Intergovernmental Panel on Climate Change’s representative concentration pathways, which are four widely cited scenarios of future carbon-dioxide concentrations in the atmosphere.

Raftery said he and his co-author Peiran Liu are working to apply their models to different geographic areas to generate results that could be useful in regional policymaking.

“It's of great interest because people are interested in what the plan is going to be, where they are; the global average is a bit abstract,” he said. 

The article, “The public health implications of the Paris Agreement: a modelling study,” was published Feb. 9 in The Lancet Planet Health. The authors of the study were Ian Hamilton, Harry Kennard, Alice McGushin and Nick Watts, University College London; Lena Höglund-Isaksson, Gregor Kiesewetter, Pallav Purohit and Peter Rafaj, International Institute for Applied Systems Analysis; Melissa Lott, Columbia University; James Milner, London School of Hygiene & Tropical Medicine; Rohit Sharma and James Woodcock, University of Cambridge; and Marco Springmann, University of Oxford. The lead author was Ian Hamilton.

The article, “Country-based emissions reductions should increase by 80% beyond nationally determined contributions to meet the 2°C target,” was published Feb. 9 in Communications Earth & Environment. The authors of the study were Peiran Liu and Adrian Raftery, University of Washington. The lead author was Adrian Raftery.

Correction: A previously published version of this article misspelled Adrian Raftery's name. The error has been corrected.