With the announcement, the U.S. joins only Nicaragua and Syria on the list of nations that have not signed on to the global agreement. A total of 194 other countries have signed on to the agreement. Syria did not sign on in the wake of the ongoing turmoil from its civil war; Nicaragua, on the other hand, wanted an agreement that did more to require its signing parties to address climate change. (Nicaragua had signed on to the 1997 Kyoto Protocol, primarily because that agreement stipulated consequences for countries that signed on but didn't meet targets.)

One prime component of the Paris Climate Agreement is that its signees' commitments to targets for things like carbon emissions are voluntary, not binding. As one example, the U.S. agreed to reduce emissions by between 26 percent and 28 percent by 2025.

Recent research suggests that even with a greater focus in recent years on the dangers of climate change, that emissions target and other targets set by signees of the Paris Agreement (including an overall world temperature rise of less than 2 degrees Celsius above preindustrial levels) were in danger of being unmet. Even with all of the targets in place, the Earth's temperature is projected to be 3 degrees Celsius higher than preindustrial levels; the ramifications of that eventuality could include longer heat waves, higher rises in sea levels, and faster ice sheet melting than are already being experienced. Already, the past three years have broken records for the hottest year.

The U.S. Senate had not ratified the Paris agreement, even though then-President Barack Obama had committed the country to abiding by the agreement. (A further 50 countries have yet to ratify.) In fact, the agreement has a formal withdrawal series of events, which will take four years to complete. Thus, the earliest date on which the U.S. could exit the Paris Agreement is Nov. 4, 2020. The next presidential election occurs on Nov. 3, 2020.

As part of the initial agreement, the U.S. has already paid $1 billion of a projected $3 billion to augment poor countries' efforts to pursue clean energy strategies and to cope with droughts and a rise in sea level. Trump has announced that the U.S. will not send any more aid in this regard.

The announcement fulfilled a promise that Trump had made on the presidential campaign trail. Among those applauding America's withdrawal from the Paris Agreement were Republican National Committee Chairwoman Ronna McDaniel, Environmental Protection Agency Administrator Scott Pruitt, and presidential strategist Steve Bannon.

Trump's announcement was not followed by other countries' announcing similar moves. Mexican President Enrique Peña Nieto reiterated his country's commitment to the Paris agreement. Other countries making similar affirmations included France and New Zealand.

Obama was among the prominent world leaders or former leaders who publicly condemned Trump's announcement. Also making their displeasure known publicly were former Secretary of State and Senator Hillary Clinton; former President Bill Clinton; U.N. Secretary-General Antonio Guterres; and the European Union's top climate change official, Miguel Arias Canente.

Trump had in March signed an executive order to rewrite Obama's Clean Power Plan, which had aimed to replace hundreds of coal power plants with wind farms and solar energy generators. The President said that he would continue to pursue those efforts.

In the U.S., commitment to the Paris Agreement was vocal at the state level. A total of 30 states have recommitted their energy strategies to pursue renewable and more efficient energy. New York Gov. Andrew Cuomo announced a plan to invest $1.5 billion in such efforts, particularly rewarding efforts to capture solar energy by schools and other public buildings. (That would be the largest ever investment by a state in renewable energy, and it is expected to create 40,000 jobs by 2020.) California's state senate has required the state's utilities to use 60 percent renewable energy by 2030 and 100 percent renewable energy by 2045. California Gov. Jerry Brown, New York's Cuomo, and Washington Gov. Jay Inslee have announced the formation of a coalition of states that were determined to continue to pursue the emissions targets set in the Paris accord.

Both Tesla Chief Executive Elon Musk and Disney Chief Executive Robert Iger resigned from the president's advisory council after the Paris announcement. Among the prominent businesses to speak out against the announcement were General Electric, IBM, Facebook, Twitter, Goldman Sachs, and the oil company Shell.

As late as a day before the announcement, Iger and Musk had joined nearly two dozen other high-profile business leaders (including the heads of Apple, Google, Intel, Microsoft, Mars, and Morgan Stanley) in publicly urging Trump not to withdraw from the Paris Agreement. Also making the same recommendation were Trump's daughter, Ivanka, and son-in-law, Jared Kushner.