Secretary of State John Kerry argued Thursday that the science showing Earth’s climate is warming because of human activity is as clear and settled as the science that shows gravity will force an apple to fall out of its tree and down to the ground.

“When an apple falls from a tree, it will drop toward the ground. We know that because of the basic laws of physics. Science tells us that gravity exists, and no one disputes that,” Kerry said in a climate speech before the Atlantic Council in Washington.

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Secretary of State John Kerry said climate change science is as clear as gravity that makes apples fall from trees, or water freezing at 32 degrees Fahrenheit. (Mandel Ngan/AFP/Getty Images)

“Science also tells us that when the water temperature drops below 32 degrees Fahrenheit, it turns to ice. No one disputes that,” he said. ”So when science tells us that our climate is changing and human beings are largely causing that change, by what right do people stand up and just say, ‘well, I dispute that, or I deny that elementary truth?’ ”

“And yet there are those that do so,” he said.

Kerry has routinely called for steps to reduce human-based carbon emissions, and said Thursday that the issue is “personal to me.” Kerry’s devotion to the issue has led some to criticize him for focusing on climate issues instead of spending more time on Ukraine, Iran or other global hotspots.

Kerry spoke for nearly an hour at the Atlantic Council, and insisted that the science behind climate change is settled.

“It may seem obvious to you, but it isn’t to some,” he said. “The science is and has and long been crystal clear when it comes to climate change.”

“It’s not particularly complicated,” he added. “I don’t mean to sound, you know, haughty about it, but think about it for a minute.”

Kerry also said the solution is simple as well.

“If we make the switch to a global clean energy economy … if we think more creatively about how we power our cars, heat our homes, operate our businesses, then we still have time to prevent the worst consequences of climate change,” he said. “It really is as simple as that.”