IF, AS BARACK OBAMA put it, the 2015 Paris Climate agreement was "the moment we finally decided to save our planet," then the executive order last week to dismantle Obama-era environmental policies is Donald Trump's "never mind."

Trump's order is a blueprint to reverse several important policies designed to fight climate change: emission rules for power plants; limits on methane gas; a moratorium on federal coal leasing; and the use of a standard called the "social cost of carbon" to guide government decisions. The main target is Obama's Clean Power plan, an EPA rule intended to cut emissions from the nation's power plants by 32 percent below 2005 levels. Even if we do not formally back out of the Paris agreement, these changes will make it impossible for the United States to fulfill our part of the bargain.

"Aside from provoking a large-scale nuclear war, it is hard to imagine an American president taking an action more harmful to the U.S.," said David J. Arkush, managing director of the climate program for Public Citizen, a citizen advocacy group.

Trump's move was not a surprise. It is just the latest in a series of moves that are breathtaking in their contempt for clean air, water and soil, and for the health and safety of the American people. Here are only a couple: a reversal of a rule that prevented coal mines from dumping their waste into local streams and a decision to ignore the EPA's own chemical experts and continue to allow the use of an insecticide harmful to farmworkers and children.

Most of the changes in Tuesday's executive order can't go into effect right away, if at all. They will require the writing of new rules - and those rules are sure to be fought in court. The executive order will be more of an employment boomlet for lawyers than it will be for the coal miners whose jobs Trump says he wants to save.

Even if the executive action is mostly symbolic, it still is reckless: It signals that U.S. climate efforts are being reversed, when the situation already is critical: If the planet were to pull out all the environmental stops and phase out the use of fossil fuels, the rise of global temperature could possibly be limited to 2 degrees Celsius (3.6 degrees Fahrenheit). That still would mean massive increases in super storms like Sandy, more wildfires, food shortages, rising sea levels that would threaten American cities like New York and Miami, among others, with devastating economic and social damage.

Without that kind of effort, the global temperature likely will go higher, throwing the world into chaos.

Perhaps Trump and fellow Republicans don't know what they don't know. Perhaps they do know but are like the wealthy "doomsday preppers" featured most recently in the New Yorker, figuring they can build sanctuaries to protect themselves from rising seas and civil unrest. It doesn't matter.

For the rest of us, it's time to act to save our children and grandchildren.

What You Can Do: Call your representatives and tell them to stand up to Trump on climate. Check actonclimate.com, a consortium of environmental groups, to find out what to say. Attend the People's Climate March in Washington, D.C. on Saturday, April 29 (the week after the March for Science). See peoplesclimate.org for more information.