Smoking causes cancer. Carbon pollution causes extreme weather.

It really doesn’t have to be more complicated than that.

We dump billions of tons of carbon pollution into the atmosphere each year. As a result, the concentration of carbon dioxide has increased by 40 percent. Excess carbon dioxide traps excess heat in the atmosphere. Excess heat causes extreme heat waves, droughts, and storms.

And that’s what we have been seeing. In June alone, 170 all-time high temperature records were broken or tied in the United States, and more than 24,000 daily high temperature records have been broken so far this year. If the climate weren’t changing, we would expect to see about the same number of record highs and record lows set each year due to random fluctuations. That’s what we were seeing 50 years ago, but during the last decade there were twice as many record highs as record lows. So far this year the ratio has been 10 to 1.

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This year’s extreme weather follows last year’s. The last 12 months were the hottest on record for the United States. Texas saw its hottest and driest summer on record in 2011 by a wide margin, and research published this week [PDF] shows that carbon pollution dramatically increased the probability of such extreme heat and drought.

Faced with similar information about the carcinogens in cigarette smoke, the mechanism by which these carcinogens cause genetic mutations, and the statistical relationship between smoking and cancer, the Surgeon General says that smoking causes cancer. Of course that doesn’t mean that every individual case of cancer experienced by a smoker can be definitively attributed to smoking. But the Surgeon General does not feel compelled to say that every time she says that smoking causes cancer. And journalists don’t feel compelled to include that caveat every time they write an article about the health toll of smoking.

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The Surgeon General’s warning hasn’t always been this clear. In 1966, when cigarette packages were first required to carry a warning, the package said “Cigarette Smoking May be Hazardous to Your Health.” A few years ago a similarly tepid warning may have been appropriate for carbon pollution. Not anymore.

The data are in. It’s time for scientists and journalists to just say it: Carbon pollution causes extreme weather.