President Donald Trump undermined the nation's security and American leadership in the world with his announcement Thursday that the U.S. would withdraw from the Paris climate agreement. The move amounts to a staggering abdication of this nation's responsibility for the warming climate, and it will encourage more countries and industries to ignore the impact of rising temperatures and seas on public health and safety. While Trump offered a vague commitment to re-enter talks to seek a more favorable deal, that is window-dressing a senseless decision, choosing to stand by his fanciful campaign promises to revive the coal industry rather than working with China and other polluters for the benefit of global health.Trump's announcement comes as no surprise. He denounced the deal during a White House ceremony much as he did on the campaign trail, delivering a dark, nationalist tirade and relying on discredited studies to characterize the agreement as a jobs-killer that would make American manufacturing less competitive, raise costs for consumers and lead to electrical outages. Trump's declaration that he "was elected to represent the citizens of Pittsburgh, not Paris'' is offensive to both Paris and the citizens of Pittsburgh, who successfully transformed their local economy after the collapse of the steel and coal industries.The agreement, struck by the Obama administration and leaders of 194 other countries, calls for nations to set voluntary targets for reducing emissions of global-warming greenhouse gases. While opponents faulted the accord for being nonbinding, the pact is a big step forward in marshaling global consensus on the threat of climate change and on the urgency to respond. The deal also provides a process for tracking international progress and for inducing countries and industries to invest in cleaner energies. With its withdrawal, the U.S. joins only two nations as holdouts — Nicaragua and Syria. That's a national disgrace.Trump's decision does not invalidate the entire agreement. But a U.S. withdrawal frees the world's other industrial states to back off their own commitments. It removes the U.S. from playing a lead role in ensuring that other nations reported their emissions accurately. And its sends a signal to businesses here and abroad that the Trump administration will not be a partner in growing the clean-energy sector and in encouraging more sustainable development.On a larger note, Trump's exit marks another retreat on the international stage. Though the pledges under Paris still would allow for a dangerous increase in warming above pre-industrial levels, U.S. participation would have brought more credibility to the process and leverage to the enforcement measures. Major companies and industries in the United States had already signaled they would move toward a cleaner energy future as natural gas and renewables made coal a costlier option; their endorsement of the Paris agreement offered hope that technological advancements would surpass the pledges made and lead to a more moderate increase in warming. Thursday's announcement takes the wind from those sails. And it leaves China, the world's top emitter of greenhouse gases, as the leader of global efforts to curb them.States such as New York and California still have plans for cleaning up power plants and vehicle tailpipe emissions. But the withdrawal from the Paris accord, combined with Trump's efforts to roll back other Obama-era climate change policies and cut or cancel research on global warming represents a new era of isolation and backward thinking for the nation. Coastal states like Florida, where rising sea levels are already threatening streets, public utilities, private property and the drinking water supply, are put particularly at risk. The global community should move ahead and wait out the Trump administration. But for the United States, this is another depressing step away from leadership in the world — and realities of a changing climate and economy at home.