On the 40th anniversary of the First World Climate Conference, more than 11,000 scientists have come together to urge immediate action on the climate crisis, The Guardian reported.

"Scientists have a moral obligation to clearly warn humanity of any catastrophic threat and to 'tell it like it is,'" a group of scientists wrote in a letter published in BioScience Tuesday. "On the basis of this obligation and the graphical indicators presented below, we declare, with more than 11,000 scientist signatories from around the world, clearly and unequivocally that planet Earth is facing a climate emergency."

The letter was written by dozens of scientists and endorsed by thousands more from 153 countries. It differs from past scientific communications about the climate crisis in that it does not speak in uncertainties and it lays out actual policy recommendations, The Washington Post pointed out. It is also the first time a large number of scientists have embraced the word "emergency" to describe climate change.

"The term 'climate emergency' … I must say, I find it refreshing, really," climate scientist and Woods Hole Research Center President Phil Duffy, who signed the letter Monday, told The Washington Post. "Because you know, I get so impatient with the scientists who just are always just waffling and mumbling about uncertainty, blah, blah, blah, and this certainly is, you know, is much bolder than that," he said. "I think it's right to do that."

Lead author and Oregon State University professor William Ripple told The Guardian he was inspired to spearhead the effort because of the uptick in extreme weather events he had noticed.

"It is more important than ever that we speak out, based on evidence. It is time to go beyond just research and publishing, and to go directly to the citizens and policymakers," he told The Guardian.

The letter writers outlined several "vital signs" of both human activities that contribute to global warming and climate impacts themselves.

"Policymakers and the public now urgently need access to a set of indicators that convey the effects of human activities on GHG emissions and the consequent impacts on climate, our environment, and society," they wrote.