The mass protests were times to coincide with Trump's 100th day in office, with the main event being the Peoples Climate March in Washington, D.C.
There, a crowd tens of thousands strong braved sweltering temperatures in the low 90s to make their way down Pennsylvania and stand before the White House to express their displeasure with the president directly at his doorstep.
Among those joining them were former Vice President Al Gore and actor Leonardo DiCaprio.
Organizers of the even said there were over 300 sister demonstrations and rallies in cities and small towns throughout the country, with the unifying theme being anger over the president's plan to dismantle the Environmental Protection Agency and roll back the climate-change policies of his predecessor, former President Barack Obama.
Speaking at a demonstration in Montpelier, Vermont Sen. Bernie Sanders called the marches part of a fight for the future of the planet.
Placards and homemade signs carried during the marches lambasted the president over his removal of restrictions on oil drilling and carbon emissions at coal-fired power plants.
The demonstrations came one week after supporters of science gathered in 600 cities both in the United States and abroad.
But the administration's response to the events was obstinate. On the very day of the climate march, the EPA removed the climate change page from its website.
And Trump himself, who left Washington for Pennsylvania early Saturday evening for a campaign-style rally to celebrate his first 100 days in office, effectively shrugged when a reporter asked him about the march.
He said he hoped the protesters enjoyed the day.
"And the weather," he added. The last comment was a bit of a jab at the thousands who assembled as the temperatures soared to a 91 degrees, tying a record set in 1974.
Elsewhere protestors gathered in snow, in pouring rain and other inclement conditions to make their voices heard. Everywhere, they spoke of the importance of addressing climate change, of promoting renewable energy and of protecting the environment.
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