Cosmos Recap: The Big Damn Climate Change Episode

Cosmos Recap: The Big Damn Climate Change EpisodeWe are down to the last two episodes of Cosmos: A Spacetime Odyssey, already. You can pretty much bet that this week’s episode, The World Set Free, is going to be the one that gets talked about the most, and probably shown in more classrooms than any other, because after making passing mentions of it in several previous episodes, this is the one where Neil de Grasse Tyson brings out the Big Science guns and talks for the full hour about climate change. This is the episode that you can tell has probably had the most editorial meetings behind it to plan out how to make the case, firmly and clearly, that climate change is real, it’s already here — not off in some distant future — and not only is the science not in dispute, but none of the “alternate” explanations hold water. And for the most part, it works impressively well.

Tyson starts us out on Venus, explaining that for the first billion years or so of the planet’s existence, things were probably a lot like conditions on the early Earth — liquid seas, the occasional asteroid strike, maybe even the beginnings of life. Almost a paradise, until the planet’s atmosphere became too filed with carbon dioxide from volcanic eruptions, which eventually led to a runaway greenhouse effect. Heat from the sun was trapped in the atmosphere, and the planet grew hotter and hotter — and not merely because of its closer proximity to the Sun. In fact, Venus’s thick cover of clouds, mostly made of sulfuric acid, would actually make its surface ice-cold, were it not for the high levels of sunlight-trapping CO2. As it is, the Venusian atmosphere is hot enough to melt lead.

tyson dover 1

When they formed, Tyson tells us, Earth and Venus had similar amounts of carbon. The difference between the two planets is largely in the form that carbon took. On Venus, it’s mostly CO2 gas, while on Earth, it’s been stored in solid form, as rocks, like the white cliffs of Dover, which make for a pretty nice shooting location — and this time, Tyson’s actually there, not just in front of a green screen image. (after he walked around on “Mars” last time, we worried that maybe Tyson never leaves a studio. And MAYBE HE DOESN’T!) The limestone and chalk cliffs are nothing more than the remains of trillions of tiny algae that absorbed atmospheric CO2 and stored it, as they do on seabeds worldwide, leaving Earth’s atmosphere with only trace amounts of CO2 — less than .03%, or as Tyson visualizes it with three colorful butterflies, “less than three molecules out of every ten thousand.” If there were no atmospheric CO2 at all, Earth would freeze; double it, to just .06%, and Earth would be a much hotter planet with no ice caps, but still far from becoming Venus. For that matter, the amount of CO2 in the atmosphere varies cyclically during the year — the planet “exhales” CO2 in the winter, when the northern hemisphere’s forests lose their leaves and they decay, and “inhales” it in the summer, a cycle only discovered in the late 1950s, when accurate measurement of CO2 became possible. And that’s when we also discovered the increase in atmospheric CO2 since the start of the industrial age.


And how do we know? Ice — cores taken from glaciers in Greenland and Antarctica, with a clear record of ancient air, trapped for 800,000 years. Until the early 20th Century, the CO2 rate never went above .03%, but after that, it’s risen sharply, with 40% more CO2 in the atmosphere than before the Industrial Revolution. Simply put, we’re “exhaling” more CO2 than the planet can “breathe” in. The Earth, warmed by the Sun, radiates heat. The more CO2 in the atmosphere, the more heat is retained, and the more the Earth warms. Says Tyson,

That’s all there is to the greenhouse effect. It’s basic physics — just bookkeeping of the energy flow. There’s nothing controversial about it.

And then Tyson sets to work debunking the claims of climate change deniers. Could volcanoes be at fault? Nope — the amount of carbon dioxide from all the world’s volcanoes is about 2% of the amount emitted by fossil fuels each year. And the amount of CO2 in the atmosphere matches quite nicely with the amount of fossil fuels we consume. And the rate of global warming also tracks to the amount of CO2 in the air. This isn’t politics. It’s math, and physics. To illustrate how much carbon is dumped into the air annually, Tyson uses a nice visual trick — CGI and green screen at last: if that annual amount, about 30 billion tons of CO2 gas a year, were compressed into solid carbon, the mass would be similar to that of the cliffs of Dover, and so we get to see the cliffs double in size, and then some, year after year. The chief byproduct of our way of life also happens to be the gas that regulates our planet’s temperature. If we could see CO2, Tyson says, then maybe we’d have more incentive to do something about it.

cosmos CO2 visible

But is the Earth really warming? Yep. Surface temperatures, atmospheric temperatures, and oceanic temperatures. And, Tyson notes, it’s not as if we didn’t see it coming. We get a brief review of climate observations, going back to the 1890s, when a paper first predicted that a doubling of CO2 could lead to the melting of the polar ice caps, to a 1938 paper noting that average global temperatures were increasing proportional to CO2, through a 1958 TV program in which a scientist warns, “even now, man may be unwittingly changing the world’s climate through the waste products of his civilization.” Carl Sagan’s 1960 PhD thesis was on Venus’s greenhouse effect, and in 1980 he too warned that we risked destabilizing our atmosphere. This stuff didn’t come out of nowhere, and never mind that one Time Magazine cover in the ’70s that speculated about Global Cooling. And since then, we’ve added another 400 billion tons of CO2.

Tyson then uses a lovely little set-piece to illustrate the difference between climate and weather, answering the idiotic “well if there’s global warming, how could we have a record cold winter last year, HUH?” (Except Neil is way too nice to call anyone an idiot.) It’s really simple: weather varies from day to day, year to year. Climate is the long-term trend of the weather’s behavior over time.


And when we’re making policy, we need to think about climate — the steady long-term trend — not the short-term variability of weather.

And then we get to the scary stuff: the melting ice caps, the rise of the oceans, and, oh dear, since ice reflects sunlight and open ocean absorbs it, the more open ocean there is, the more warming, and the less sea ice — a positive feedback loop. There’s some genuinely Oh-My-God time-lapse photography of a section of Arctic shoreline — land and permafrost — peeling away and falling into the sea, and Tyson explains another feedback loop: as the permafrost thaws, plant matter that had been frozen for millennia rots, releasing more CO2 and methane (an even worse heat trapper) into the atmosphere. More erosion, more storms. We genuinely could be tipping past a point of no return.

OK, but what if it’s not our fault? Can we blame the Sun? Nope. Solar energy output hasn’t changed, and we’re warming more in the winter than in the summer, the opposite of what you’d expect if solar heat were to blame. It keeps coming back to the stuff we burn to make our machines run, to make electricity. Ah, says Tyson, but the Sun is the solution, and then we get a couple of brief animated segments about early inventors of solar technologies: Augustin Mouchot, who in 1878 demonstrated a solar powered boiler that could run an ice machine — ice from the sun! Unfortunately for Mouchot, coal was cheap and plentiful. And then there was Frank Shuman, an American who in 1913 hoped to make the Sahara Desert bloom with solar collectors that ran water pumps — but then oil was cheap and plentiful, and WWI broke out. Schuman’s solar arrays were torn up and scrapped to make weapons.

After driving home the massive bummer of just how precarious our situation is, Tyson closes with hope, and not unrealistic hope, either. Solar and wind technologies are becoming more economically competitive, and have virtually none of the environmental consequences of fossil fuels. (Wind turbines may “whoosh” some, and that upsets people, we’ve read.) Like Sagan before him, Tyson is worried, but a cautious optimist. We are, after all, a remarkably adaptive, inventive species, and we’ve managed some impressive feats of survival. We’re no longer on the brink of incinerating ourselves in a nuclear war, for instance. Mutual Assured Destruction is largely just a phrase to be learned in history classes. And even from that madness, we also launched the Apollo program, and the race to build bigger and better rockets to deliver warheads evolved into the machines that allowed us to see our home planet, that pale blue dot, from the Moon. And out of the Cold War came the iconic image of a world full of life, against the blackness of space, the only home we have for the foreseeable future. From deadly competition, we at least saw the possibility of peace.

Transitions aren’t easy, Tyson says, over an aerial view of ancient terrace farms in the Philippines — moving from life as nomadic hunter-gatherers to life as farmers took adjustments (and no doubt, there were some who said it just couldn’t be done — if we stay in one place, we’ll run out of game!). There are no scientific or technological barriers to stopping and even reversing climate change, although of course it won’t be easy. The question, he says, “is what we truly value… and whether we can summon the will to act.”


So will Cosmos change minds? Every week after watching, I read the Reddit discussion of the latest episode. And this week, this is the top-rated comment:

I am a conservative libertarian (not that it really matters what my political ideology is lol), I have always kind of doubted that us humans are the cause of the warming. I’ve always thought that we have just been going through another cycle that the earth has always gone through. And I thought this issue was just so politicized (which to be fair, it is highly politicized) that I just didn’t know how to even begin to get a straight answer on this issue.

This one episode has totally changed my mind on this issue. There was no political rhetoric to try to sift through. It was JUST the science, explained in a simple way so anyone can understand. Neal DeGrasse Tyson went through all of the reasons that earth could be heating up, and explained why they could or couldn’t be a contributing cause. There was one graph that really shocked me. It was the one showing the amount of CO2 in the atmosphere, and it showed how insanely high it sky rocketed in the 20th century.

This is exactly what I needed to be able to see that yes, we are doing this, and we need to fix it. I love this show, and I learn something every time I watch it. I never thought my mind would be changed on such a polarized issue like this.

So there’s one mind, changed. It’s a good start.

Cosmos: A Spacetime Odyssey airs on Fox 9:00 Sundays Eastern/Pacific, 8:00 Central/Mountain. Reruns Monday on National Geographic Channel 10:00 Eastern. Episode 12, “The World Set Free,” online at

TV Show: Cosmos

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