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Forty-six years after environmentalists dedicated April 22 to Earth, the United States and China will sign the Paris Agreement to reduce global greenhouse gas emissions and combat climate change.
In light of the historic deal between the world’s two largest polluters, we look back on some of our recent fact-checks on the issue.
Here are six things everyone should know about climate change.
1. The vast majority of experts say humans are contributing to climate change.
Most scientists agree that climate change is real and humans are causing it. The figure that’s widely cited is 97 percent of climate scientists, and it appears in at least three peer-reviewed surveys. Plenty of other studies report overwhelming majorities of experts (in the 90 percent range) and at least 18 scientific associations agree.
2. Climate change has national security implications.
In recent years, the Obama administration, the United Nations Security Council, and many foreign policy and military defense experts have all named climate change as a national security risk. The Pentagon calls it a "threat multiplier," meaning it can lead to food and water insecurity, increased poverty and disease, mass migration and instability.
That’s what happened in Syria, according to a credible 2015 study. The cascading effects of climate change — drought, famine, disease, displacement — contributed to the Syrian conflict in 2011 and bred the conditions for terrorism and the Islamic State to operate.
3. But that doesn’t mean the government is prioritizing climate change over other security concerns.
Those who reject the mainstream climate science often criticize the government for pushing a green agenda while ignoring terrorism. Many of these claims are inaccurate.
The Obama administration is not, for example, sparing ISIS oil fields from bombing because of "concern about global warming," as Ted Cruz claimed. The U.S. military has been striking the terrorist group’s oil assets in a limited fashion, but if climate change were the top concern, it actually would make more sense to ramp up the bombing to stop oil production.
Nor is Obama funding the fight against climate change in lieu of violent extremism, as Wisconsin Rep. Sean Duffy said. The Department of Homeland Security did budget $16 million for climate change in 2016, but multiple government agencies are spending millions more for countering extremists.
4. Nor has concern for climate change altered behaviors, opinions or the energy market that much.
Despite the attention on climate change, Americans are still driving gas guzzlers while alternative energy sources lag behind oil and coal.
SUV sales reached their highest ever market share in 2015 and carpooling is down nearly 20 percent since from 1980. Meanwhile, 56 to 60 percent of the public has consistently supported the Keystone XL pipeline that opponents say will increase greenhouse gas emissions and increase the risk of water population.
5. Climate change leads to temperatures at historic levels, and that leads to fatalities.
With a combined global land and ocean average temperature of 58.22 degrees Fahrenheit, the first 11 months of 2014 were the warmest on record. Then 2015 overtook it, with an average global temperature of 58.62 degrees. And the first three months of 2016 have already surpassed marks set in 2015.
According to the World Health Organization, as many as 250,000 people will die every year from heat exposure from 2030 to 2050, with the greatest fatality rates in the world’s poorest countries.
6. With all this happening, some Republicans are warming up to the idea of addressing climate change (but not the GOP frontrunner).
In 2014, we rated a claim that "virtually no Republican" in Washington accepted climate change science Mostly True. At that time, very few members of Congress were on record as accepting climate change.
In 2015 and 2016, however, the GOP’s presidential field seem to be largely on board with the notion that that climate change is happening. Candidates such as John Kasich, Jeb Bush, Chris Christie, Carly Fiorina, Lindsay Graham, Bobby Jindal, Jim Gilmore, and George Pataki all agreed that it’s man-made. And they all called for some degree of action to combat it, though none of them except Jindal outlined specific proposals. (Democrat Hillary Clinton has an in-depth proposal, as does Bernie Sanders.)
Marco Rubio and Rand Paul said it’s real but humans aren’t to blame, while Donald Trump, Ted Cruz, Mike Huckabee and Rick Santorum flat-out deny that the climate is changing.
(Bonus: You can read our other coverage of environmental issues, including fact-checks about fracking, plastics, fish in Miami, panther attacks, vegans, GMOs and butterflies, GMOs and zika, chemicals and much more.)
See individual fact-checks for sources