Failure to Slow Warming Will Set Off Climate ‘Tipping Points,’ Scientists Say

A group of scientists said on Thursday that failure to limit global warming to the targets set by international accords will most likely set off several climate "tipping points."

The researchers said that even at the current level of warming, about 1.1 degrees Celsius (2 degrees Fahrenheit) above preindustrial levels, some of these self- sustaining changes might have already begun. The changes would become much more certain if the goal of two targets set by the Paris Agreement is reached.

The loss of mountain glaciers and the collapse of a system of deep mixing of water in the North Atlantic are likely to be set off at the higher Paris target.

The changes would affect life on the planet. Sea level rise would be measured in feet, not inches, as a result of the collapse of the glaciers. Efforts to limit warming would be hampered by the release of more heat-trapping gases. Global temperatures could be affected by a shutdown of ocean mixing in the North Atlantic.

The director of the Potsdam Institute for Climate Impact Research in Germany said that the team had come to the very dire conclusion that 1.5 degrees Celsius is a threshold beyond which some of these effects would start. He and others said that cutting emissions of carbon dioxide and other heat-trapping gases is more important than ever.

The research is in line with recent assessments by the Intergovernmental Panel on Climate Change, a group of experts convened by the United Nations.

McKay is the lead author of a paper about the work that was published in Science. Warming to 1.5 degrees doesn't mean we don't see tipping points. It reduces the chance.

Overshooting the target does not mean that everything is lost. Dr. Rockstrm said that every tenth of a degree counted. It's better to have 1.6 than 1.7 and so on.

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The climate and energy legislation passed by Congress last month moves the United States closer to its own goals, despite the fact that countries have not pledged to cut greenhouse gas emissions enough to meet either Paris target. Warming by the end of the century is projected by current policies. More tipping points would be set off at that level of warming.

Climate tipping points have been around for a long time. It has been accompanied by a high degree of uncertainty and debate, including about the threshold temperatures beyond which some changes would begin, and whether some of these events even meet the definition of changes that would be self-sustaining.

More than a dozen parts of Earth's system are at risk of reaching a tipping point. Nine of the 16 parts identified by the new research would have global effects.

The summer sea ice was one of those eliminated. He said there wasn't a clear threshold beyond which the decline would become self- sustaining.

The main goal of the new research was to reduce the uncertainty about when the tipping points would be reached.

Dr. Rockstrm said that the study put temperature thresholds on all the elements. This is the first time that has ever been done.

Bill Hare, who is the chief executive of Climate Analytics, a nonprofit research and policy organization, was not involved in the study.

He said that it reinforced the urgent need for the global community to get to net zero by the year 2050.

Thomas Stocker, a climate scientist at the University of Bern in Switzerland, was not involved in the study. He said that the study's findings are not the final word. It is a contribution to an ongoing discussion.

A comprehensive analysis by the Intergovernmental Panel on Climate Change is what is needed, according to Dr. Stocker.

More research was needed according to Dr. Rockstrm. He hopes that the I.P.C.C. will accept the scientific assessment.

A conference will be held next week to encourage more work on the topic. Modeling of these cataclysmic events is one of the projects Dr. Rockstrm is working on.

He said that they are in a better position now than they were a few years ago.