Sen. Bernie Sanders, I-Vt., said President Trump's "days are numbered" for ignoring climate change in his State of the Union address and supporting fossil fuels over cleaner sources of energy.

"What we are about is telling Donald Trump and the Koch brothers, and all of these people, that their days are numbered, fossil fuel’s days are numbered, we are going to transform our energy system," Sanders said in his opening address at a climate summit Wednesday in Washington, D.C., hosted by the anti-fossil fuel activist group 350.org and its founder Bill McKibben.

The summit was used as both a response to the Trump agenda and the president's Tuesday night address, as well as to initiate a nationwide campaign called "Fossil Free" aimed at ending all fossil fuel use.

“What an outrage," Sanders said. Trump “somehow forgot to mention the words climate change” in his first State of the Union address, he said.

“We should not be surprised, Donald Trump, one of the great scientists of our time, has determined after years and years of exhaustive study that climate change is a ‘hoax' brought to us from China,” Sanders quipped.

Sanders renewed his call for politicians to not take money from fossil fuel companies and contributors, underscoring that the political network overseen by the Koch brothers has vowed to inject nearly $400 million into the upcoming midterm elections.

He said that is a huge sum of influence coming from just a "handful of billionaires," which makes the upcoming elections a fight for “nothing less than the future of this planet.”

The summit emphasized the importance of resisting the fossil fuel industry and supporting a move to transition to 100 percent renewable energy. McKibben called on the more than 30 groups at the "resistance" conference to oppose fossil fuel projects.

He said that Trump will not impose a "carbon tax" anytime soon, but that the groups' resistance to fossil fuel projects will act as a tax on carbon dioxide pollution.

Many scientists blame carbon dioxide for causing the Earth's temperature to rise, causing more severe weather, drought, and flooding.