Moreover, national commitments to slash emissions made in Paris are voluntary. Countries can modify or ignore them. There is no enforcement or penalty for missing targets. 

Under the Paris accord, countries made these commitments based on their own circumstances and political judgment. The United States pledged to cut greenhouse gas emissions by 26 to 28 percent from 2005 levels by 2025. The European Union promised to reduce emissions by 40 percent from 1990 levels by 2030. China said that its carbon dioxide (CO2) would peak by 2030 and that, by the same year, renewable fuels would represent about 20 percent of its energy use.

But as noted, none of these goals was binding. There was little, if any, loss of national sovereignty. The Trump administration could have accepted what it liked (presumably, cheap natural gas with lower CO2 emissions) and rejected what it didn’t (say, the tougher vehicle fuel mileage standards). To make the same point slightly differently: Trump’s actions were mostly symbolic and political. They were grandstanding, intended to impress his core supporters.

This distorts the climate debate in a dangerous and deceptive way. It’s become all about Trump, when it should be about the inherent difficulty of regulating the global climate. The main practical consequence of Trump’s stubborn stance is to offend (needlessly) the nearly 200 other countries that support the Paris accord. Trump’s foreign policy seems to be a calculated effort to lose the United States as many friends in the world as possible. It’s madness, a new strain of isolationism. 

It also sends the wrong message: If only Trump would come to his senses, we could get on with the serious business of solving climate change. Trump is allegedly the big obstacle -- his apparent unwillingness to admit human-induced warming -- just as greedy oil companies were before him (most big oil firms now seem to have shifted). The truth is more complicated.

We can’t predict the exact degree of warming. Still, the direction is clear. Even if the Paris accord were fully implemented and all countries met their commitments -- now impossible outcomes -- emission levels would remain high, just lower than they would otherwise be, says Kelly Levin of the World Resources Institute, an environmental group. Although warming would slow, temperatures would continue rising. 

Here’s why. 

Growing concentrations of CO2 and other greenhouse gases in the atmosphere are the culprits. They increase temperatures by trapping heat close to the surface. The emissions come mostly from the burning of fossil fuels (oil, coal, natural gas). Even if emission amounts decline, they’re still adding to CO2 concentration levels -- just at a slower rate. Because concentration levels matter, warming proceeds. 

To stop this process requires replacing most fossil fuels -- a daunting and perhaps impossible task. People won’t surrender their vehicles, air conditioners and computers. It’s true that wind and solar have made huge gains, but they started from low bases. With or without Paris, fossil fuels remain the foundation for modern civilization. According to data from the U.S. Energy Information Administration, fossil fuels accounted for 83 percent of world energy in 2015, down only slightly from 85 percent in 1990.

Based on present technology and knowledge, we don’t know how to solve global warming. There is no obvious way to eliminate our pervasive dependence on fossil fuels without plunging the world into a prolonged depression and inviting widespread civil strife. 

This is not an excuse for fatalism -- doing nothing -- nor an exoneration of President Trump’s casual dismissal of the Paris accord. Global warming exemplifies what economists call a “collective action” problem: Unless all major nations cooperate, little can be done. A U.S. carbon tax (as often suggested by this writer) would be a good start. It would favor energy efficiency and renewables, as well as reduce chronic budget deficits. 

But what we most need is honesty, which is scarce. The right dismisses global warming as a fake problem; the left can’t acknowledge that, as yet, there are no viable solutions. We need to keep searching and hope that something turns up.