DENVER -- Hundreds of thousands of people gathered all across the world on Earth Day as part of the March for Science.

In the United States, scientists are worried President Donald Trump's budget cuts will impact research and science-based policy.

Political attacks against President Trump were constant at Civic Center Park in downtown Denver on Saturday.

"He hasn't done anything he promised during the election," said one person at the march. "He is letting down his base."

Another person at the march responded to Trump's continued message of bringing back American jobs in the coal and steel industries.

"Without clean water, without clean air, jobs don't mean crap."

On Saturday afternoon, Trump issued an Earth Day statement, saying the U.S. has an "obligation" to protect its resources while "reducing unnecessary burden" on the economy.

You can read the whole statement below:

Many scientists have been grilled on just how much humans have affected the climate. But despite the push back from politicians and a section of the public, most scientists agree: climate change is real and it is being sped up by actions of human beings around the world.

MORE: Why people are marching for science across the world

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GALLERY: Thousands march for science in downtown Denver