But we can object to how the critics manipulatively use this point. A study published Thursday in Environmental Research Letters shows why.

The Post’s Chris Mooney reports that “climate change could lead to sea level rises that are larger, and happen more rapidly, than previously thought,” citing a trove of new research on how polar ice melts and collapses. According to one paper, “in one scenario assuming high fossil fuel use and strong economic growth during the century, the study predicted that seas could rise by as much as 4.33 feet on average — with a high end possibility of as much as 6.2 feet — by 2100. That includes possibly rapid sea level rise as high as 19 millimeters per year by the end of the century. These numbers are considerably higher than high end projections released in 2013 by the Intergovernmental Panel on Climate Change.”

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But, Mooney explains, “if the world limits global warming to the Paris climate agreement emissions target, the study finds that sea level rise might be held as low as 1.7 feet by 2100, on average.” This result would not be guaranteed; governments would have to keep cutting emissions after hitting their 2030 Paris targets. But the study nevertheless finds that meeting the agreement’s medium-term goals, which Obama’s climate policies were designed to do, would keep a path open to averting truly disastrous sea level rise.

In other words, the practical climate benefits of U.S. global warming policy are real — this is just one of many examples — but mostly visible when combined with other nations’ work. Europe has done much more than the United States to cut emissions, but if other countries did not join in, the effort would amount to relatively little. If, on the other hand, major countries such as the United States and China cooperate, the seas would not rise as much. “Obama-era clean energy policies would help restrain sea level rise, possibly by several feet” sounds much less futile, but it is just as correct as saying that these policies could not single-handedly stop the planet from warming.

Pointing out that the United States acting alone could not solve global warming, meanwhile, is no great insight. The critics merely restate the problem that global accords such as the Paris agreement were designed to address: The planet’s major nations must work together or fry separately. China and Europe, each of which seems far more serious about addressing climate change than the Untied States at the moment, harbor the same fears Americans do that they will cut emissions while other nations do nothing.

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As the world’s second-largest CO2 emitter and the largest historical emitter, the United States bears a particular responsibility to lead, or, at least, actively participate, in this effort. Instead, President Trump trashed the Paris agreement, along with the policies meant to get the United States to the Paris emissions target to which Obama had committed. Trump’s behavior has become one of the greatest threats to global accord, making it more likely that whatever the United States continues to do to cut emissions will not be met with similar levels of ambition abroad.