Eleven thousand scientists from across the globe wrote a letter Tuesday warning that “untold human suffering” will happen if the governments of the world don't act immediately to combat climate change.

The letter, which was published in BioScience Tuesday, says that "climate change has arrived and is accelerating faster than many scientists expected.”

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“Despite 40 years of major global negotiations, we have continued to conduct business as usual and have failed to address this crisis," Oregon State University ecology professor William Ripple, one of the main authors of the letter, told The Independent.

According to the publication, the letter focuses on six major objectives that scientists believe are crucial: replacing fossil fuels, cutting pollutants, restoring and protecting ecosystems, eating less meat and making the world economy carbon-free.

Thomas Newsome, another lead author of the letter, added that "while things are bad, all is not hopeless. We can take steps to address the climate emergency."

Optimism can be found in the rise of renewable energy, declining birth rates and increased world activism, according to the letter.

“We are encouraged by a recent surge of concern," the scientists wrote. "Governmental bodies are making climate emergency declarations."

The group continued: "Schoolchildren are striking. Ecocide lawsuits are proceeding in the courts. Grassroots citizen movements are demanding change, and many countries, states and provinces, cities, and businesses are responding."

The letter comes the day after President Trump Donald John TrumpFederal prosecutor speaks out, says Barr 'has brought shame' on Justice Dept. Former Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick MORE began the yearlong process of withdrawing the U.S. from the Paris climate accord, which is signed by every other country in the world.