Why It Matters: Climate Change

WASHINGTON -- THE ISSUE: It's as if Hillary Clinton and Donald Trump live on two entirely different Earths: one warming, one not.

Clinton says climate change "threatens us all," while Trump tweets that global warming is "mythical" and repeatedly refers to it as a "hoax." Measurements and scientists say Clinton's Earth is much closer to reality.

As heat-trapping gases in the air intensify and hot temperature records shatter, global warming is taking a toll on Americans' everyday life : their gardens, air, water, seasons, insurance rates and more.

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WHERE THEY STAND

Trump calls attempts to remedy global warming "just a very, very expensive form of tax." He tells coal miners he'll get their jobs back. Solar power now employs four times more people than coal mining.

Clinton proposes to spend $60 billion to switch from dirty fossil fuels to cleaner energy. She says clean energy is needed, otherwise it would "force our children to endure the catastrophe that would result from unchecked climate change." She promises to deliver on the President Barack Obama's pledge that by 2025, the U.S. will be emitting 30 percent less heat-trapping gases than in 2005.

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WHY IT MATTERS

Dozens of measurements show Earth is warming. And it's worsening. The overwhelming majority of climate scientists and nearly every professional organization of scientists have said climate change is real, man-made and a problem.

The last 15 months in a row have set records globally for heat, according to the National Oceanic and Atmospheric Administration. The world is on pace to break the record for hottest year, a record broken in 2010, 2014 and 2015. The five hottest years recorded have all been from 2005 on and it is about 1.8 degrees warmer than a century ago.

But it's more than temperatures. Arctic sea ice keeps flirting with record low amounts. Hot water has been killing coral as never before seen. Scientists have connected man-made climate change to extreme weather , including deadly heat waves , droughts and flood-inducing downpours . They even have connected it as one of several factors in the Syrian drought and civil war that led to a massive refugee crisis.

Climate change is causing the seas to rise , which threatens coastlines . Sea level has risen a foot in the waters around New York City in the past century, worsening flooding from Superstorm Sandy.

And it is making people sicker with worsened allergies and asthma, heat deaths, diseases spread by ticks and mosquitoes, dirtier air and more contaminated water and food, a federal report said in April.

Changing the world's economy from burning fossil fuel, which causes global warming, has a huge pricetag. So does not doing anything. The world's average income will shrivel 23 percent by the year 2100 if carbon dioxide pollution continues at the current pace, according to a 2015 study out of Stanford and the University of California Berkeley.

Just the Obama administration's efforts to cut carbon pollution from 1,000 power plants projects to cost about $8 billion a year, but save several times more than in reduced health problems.

The world's largest general scientific society warns of "abrupt, unpredictable, and potentially irreversible changes with highly damaging impacts."

It may seem improbable that government action can restore balance to something as vast as the climate. But presidents Ronald Reagan and George H.W. Bush showed that big things can be done about air pollution. They took steps that reduced ozone depletion and acid rain .

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This story is part of AP's "Why It Matters" series, which will examine three dozen issues at stake in the presidential election between now and Election Day.