President Trump thinks climate change is a hoax; President-elect Joe Biden knows it is an existential crisis. That is one of the most consequential differences between the 45th president and the 46th, not just for the United States but also for the world.

Biden has pledged that on his first day in office he will apply for the United States to rejoin the Paris agreement to limit global warming. He has announced he will name John F. Kerry — who, as secretary of state, was a major architect of the Paris accord — as his climate envoy, making Kerry the first member of the National Security Council to focus expressly on the subject. And he plans to mandate climate-friendly policies in all government agencies, making the issue a top-shelf priority.

None of this will magically save the day for Planet Earth. None of it plugs carbon-belching smokestacks in China and India or halts deforestation in the Brazilian Amazon. But making the world’s leading superpower once more part of the solution, instead of part of the problem, is a necessary step — a prerequisite for effective global action. Humanity, and the fragile ecosystem we call home, will have a fighting chance.

United Nations Secretary General António Guterres sounded apocalyptic Wednesday in a speech at Columbia University. “The state of the planet is broken,” he said. “Humanity is waging war on nature. This is suicidal. Nature always strikes back — and it is already doing so with growing force and fury.”

Simultaneously, the World Meteorological Organization — a U.N. agency — released a “State of the Global Climate” report indicating that 2020 will go down as one of the three warmest years on record, with the period of 2011 through 2020 being the warmest decade on record. Because of human activity, atmospheric concentrations of heat-trapping greenhouse gases — carbon dioxide, methane and nitrous oxide — have reached record highs.

The warming is uneven, with the Arctic heating up much more rapidly than the rest of the globe. On June 20, the temperature in the Siberian town of Verkhoyansk reached 100 degrees Fahrenheit — the second time since record-keeping began that triple-digit heat was recorded north of the Arctic Circle.

It is hard to focus on more than one catastrophe at a time, and we’ve all been preoccupied with the covid-19 pandemic. But this year we’ve also had fires in California so vast that their smoke turned the sky an eerie orange in the San Francisco Bay area; punishing heat waves in many parts of the country; a devastating derecho in Iowa; and so many Atlantic hurricanes that those in charge of such things ran out of A-to-Z names and had to start in on the Greek alphabet for the surplus. Scientists have long predicted that human-induced global warming would generate more of these freakish extreme weather events.

So what difference will the advent of the Biden administration make to this calamity-in-progress? Off the bat, Biden and his team will encourage political and market forces that are already helping the world begin to move away from fossil fuels toward more sustainable energy sources.

Trump defiantly and stupidly tried to reverse these trends. He tried his hardest — with no real success, happily — to boost the production and use of coal, the dirtiest fuel. He moved to dismantle automotive fuel-economy standards that aimed to reduce carbon emissions. On the way out the door, he is rushing to award oil and gas drilling rights on pristine federal land in Alaska.

But public attitudes are changing. Gallup found in a poll last year that 65 percent of Americans would favor protecting the environment even if it meant curbing economic growth.

Meanwhile, the price of energy derived from renewable sources such as solar and wind has plummeted. Nobody is building new coal-fired power plants in this country. It is a huge problem that such plants are still coming online in China and India, but we will have a better chance of changing that fact if we’re participating in the Paris process rather than heckling from the sidelines.

Biden’s ambitious vision is to see economic growth and clean energy not as either-or but as both-and. The innovation and retooling necessary to reach net-zero carbon emissions by 2050 — Biden’s ambitious goal — can be a powerful engine of growth. Adaptation to the warming that is already in motion and cannot be stopped will require extensive new infrastructure, which will potentially create millions of jobs.

Even the “America First” crowd should be able to see that if we don’t lead the world into the clean-energy future, China will. Biden has to make climate action his most important legacy. He really has no choice.

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