Of all Trump’s bad ideas, pulling out of the Paris accord is the most dangerous.

The world is, without a doubt and without a credible opposing argument, heading pell-mell toward environmental disaster because of humanity’s continuing reliance on burning fossil fuels to create energy. Among the leading culprits is the U.S., which has burned coal, oil and other fossil fuels en route to developing the wealthiest economy in global history.

But instead of working with the rest of the world to try to undo the damage, President Trump is now making good on his campaign pledge to withdraw the U.S. from the 2015 Paris agreement, the effort by 195 nations to try to do something about our warming climate. He submitted formal notice to the United Nations Monday to start the yearlong process of withdrawing from the pact, though in truth, his polices have been actively undercutting it all along.

Of all the dangerous, ignorant and insupportable decisions by this administration, pulling out of the Paris agreement stands tallest. In that single act, the president is making it all the more difficult for the world to curtail emissions of carbon and other greenhouse gases that are already melting glaciers and polar ice, raising the levels of the seas, fueling larger and stronger hurricanes and other devastating storms, exacerbating — paradoxically — both droughts and floods and making areas of the earth uninhabitable for human life.

None of this is of concern to the president, who disregards the clear and overwhelming scientific consensus, the conclusions of analysts across government agencies — including the Pentagon, which lists climate change as a national security threat — and basic common sense in his dangerous quest to make the U.S. the world’s dominant source of oil and natural gas. Even members of the oil industry have come around to recognizing the perils of their endeavors, but not Trump.

The challenge for the world is to reduce greenhouse gas emissions as sharply and as quickly as possible, and even that will not be enough to avoid the effects of climate change. The Paris agreement set a global century-end target of keeping temperatures from rising by 2 degrees Celsius over pre-industrial levels, with a preferred goal of 1.5 degrees Celsius. We’re already about 1 degree above pre-industrial levels, with most of that increase coming in the last 35 years.

We must do more. We must do better. The Paris agreement, albeit insufficient, is a crucial step by world leaders to try to save us from ourselves. The Obama administration was the main driver behind it; Trump, instead, seeks to lead the nation in the opposite direction by expanding oil and gas production, ratcheting back fuel standards for motor vehicles and ignoring both the moral and economic imperatives of combating global warming. Even if he is defeated in 2020, this decision will cost the world valuable time we can’t afford to lose.