Climate pledges, if fulfilled, may prevent worst of global warming

Published on
November 5, 2021

More than 100 countries have issued new commitments to reduce greenhouse gas emissions ahead of the COP26 climate summit in Glasgow. If these climate pledges are fulfilled, global warming within the 2-degree limit could be realized.

This is the conclusion of a new study published in the journal Science. The study assessed those new pledges and how they could shape the Earth's climate. According to the authors, these pledges make it likely that global warming will be limited to 2 degrees Celsius or less this century. Under the pledges of the 2015 Paris Agreement, the chances of limiting temperature change to below 2 degrees Celcius by 2100 was an 8 percent. A smaller increase of 1.5 degrees was already no longer feasible in this scenario.

Worst climate scenario ruled out

The authors of the study estimate that with the new pledges, those chances increase to 34 and 1.5 percent respectively. These pledges must then be fulfilled and acted upon in the short term. If countries strike an even more ambitious path after 2030, those chances become even more likely, rising to 60 and 11 percent, respectively. The likelihood of global temperatures rising above 4 degrees Celsius could be virtually eliminated. At the 2015 pledges, the probability of such a warming was still 10 percent.

“We are so much closer to getting to the 2-degree goal than six years ago when the Paris Agreement was first signed,” said corresponding author Haewon McJeon, a research scientist at the Department of Energy’s Pacific Northwest National Laboratory. “The wave of strengthened climate pledges and net-zero targets significantly increased our chance of staying under 2 degrees Celsius. And we practically ruled out the possibility of the worst climate outcomes of 4 degrees or higher.”

More ambition needed for 1.5-degree limit

To make the 1.5-degree Celsius limit more likely, more ambition is needed, warned lead author Yang Ou, a postdoctoral researcher at the Joint Global Change Research Institute. "There is roughly a one-in-three chance that we will stay below 2 degrees Celsius," Ou said. "But even with more ambition, we are still far from maximum warming of 1.5 degrees in this century."

The researchers used an open-source model (the Global Change Analysis Model) to simulate a spectrum of greenhouse gas emissions scenarios. At one end of this spectrum is a hypothetical future in which current climate policies and measures remain unchanged until 2100. At the other end is the scenario in which countries commit to ambitious targets to reduce greenhouse gas emissions and absorb carbon globally. The authors then looked at what each scenario does to global warming on this spectrum. In this way, the model illustrates how climate ambitions lead to certain temperature increases.

Meeting commitments

Several factors have already changed short-term emissions and long-term climate outcomes, the authors say. Examples include the global shift from coal to new technologies, such as solar panels and electric vehicles, which are becoming more affordable. These developments, they say, have already helped bring the Paris Agreement goals closer.

Professor Niklas Hoehne of WUR's Environmental Systems Analysis chair group, provided the most recent greenhouse gas emission trajectories of all major countries for this study. He too sees that remarkable progress has been made. "Yet we are not there yet. With the wave of national pledges, the temperature limits from the Paris Agreement are within reach. But meeting these long-term goals also requires short-term policies. No country has this in place yet. Our study shows that we can stay within temperature limits, if commitments are ambitious and fulfilled."