# Just how long have we known about climate change anyways?

– Global warming, climate change, whatever people are calling it these days, it hasn't been around for that long, right? (ding) Well actually, a fascinating international cast of characters has been studying our planet's climate for almost 200 years. It started back in the 1820s with a smart French mathematician called Joseph Fourier. He figured out that, according to basic physics, our planet should be a lot colder than it is now, about 60 degrees Fahrenheit or more than 30 degrees Celsius colder. So why isn't it? Some 30 years later a smart American woman gave him the answer. In the 1850s, Eunice Foote, ran experiments to show that our planet has a natural blanket built into the atmosphere. This blanket is made up of heat trapping gases like carbon dioxide and methane and water vapor. The sun shines down and a great deal of it's energy goes right through that invisible blanket. The sun's energy hits the earth and the earth heats up and gives out heat energy.

But guess what? Just like a blanket traps our body heat on a cold night, this natural blanket traps the earth's heat keeping us, again, almost 60 degrees warmer than we would be otherwise. If it weren't for this amazing natural blanket, our planet would be a frozen ball of ice. Burr. But it didn't take too long for our next science hero, an impressively bearded Irish physicist named John Tyndall to grasp the stunning implication's of Eunice's work. Human activities can affect the thickness of this blanket. Specifically by digging coal and oil and natural gas out of the ground and burning it, we are pumping massive extra amounts of carbon into the atmosphere, carbon that would otherwise stay buried in the ground for millions of years. And what does a thicker blanket do? Well, of course, it traps more heat. How much more? In the 1890s, a mustached Swedish scientist named Svante Arrhenius calculated how much the earth would warm if we doubled or tripled the thickness of the extra carbon blanket in the atmosphere. His numbers were amazingly similar to what we get from our biggest, most modern super computers today.

But he did it using a pen and paper, 120 years ago. Here's the thing though, we know that climate has changed in the past when there weren't any humans around. Anyone who's watched the Ice Age movies or seen a documentary about a woolly mammoth knows that. So what was going on way back then? How do we know we're not just getting warmer after the last Ice Age? A Serbian engineer called Milutin Milankovitch answered that one. He originally studied concrete of all things. But during World War I, he was arrested simply for being a Serb and he got out of the prison camp on the condition that he would keep his nose in the books for the rest of the war. He decided to study the Ice Ages. And after going back some 600,000 years in his calculations, he figured out that they are caused by changes in the shape of the earth's orbit around the sun and by the tilt of the axis. Overtime, these cycles caused the great continental ice sheets to expand and retreat.

So how do we know that's not what's happening right now? Because the warming after the last Ice Age peaked 8000 years ago. That's right. According to Milankovitch's cycles, we should be gradually sliding into the next Ice Age over the next few thousand years. That was supposed to be the next event on our geologic calendar. But that long slow slide came to a screeching halt when the Industrial Revolution kicked off and we started burning all that coal, oil and gas to heat our homes and power our factories and eventually even run our cars. Don't get me wrong, I actually think a little warming is a good thing. No one wants to end up in another Ice Age, that would be terrible. We want a nice stable climate. But today, we've unleashed so much carbon that we are way past that stable climate. The earth has already warmed about one degree Fahrenheit or about .6 degrees Celsius.

And over the rest of this century we could see a total warming of anywhere from 1-1/2 up to eight degrees Celsius or three up to 15 degrees Fahrenheit depending on the energy choices that we make that will affect the thickness of our planet's blanket in the future. With that much warming, we're heading into unknown territory. Unknown that is since the time of the dinosaurs when there weren't any ice sheets, when sea level was more than 300 feet higher than today and when the land where 1/3 of the people on this planet currently live, would have been under water. And that in a nutshell is one of the biggest reasons we care about climate change. Because our human society is not built to deal with it. We've known about this climate change thing for a really long time.

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