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Cosmos: A Spacetime Odyssey, Episode 12, “The World Set Free”

For its penultimate episode, Cosmos returns to the subject of climate science, a familiar variation on a sermon it’s already preached more than once. I have some mixed feelings about this. With the series pressing against time constraints, I worry about the lost opportunities that inevitably result from retreading the same ground, when that time could have been devoted to the scientific advances that have come about since the original (for example, we’ve still heard nothing about dark matter and dark energy, or the proliferation of extrasolar planets). On the other hand, I can’t deny that climate change is by far the greatest and most urgent danger to our civilization, and gets nowhere near the media attention that it should.

And it opened with a striking visual: a flight over the surface of Venus, once a beautiful blue world like our own, now a hellish crucible, heated to a perpetual boil by a runaway greenhouse effect. The tipping point between heaven and hell is more delicate than you might think, a point brought home with a depiction of the molecular composition of the atmosphere as a cloud of butterflies. CO2 is a tiny part of the whole – for most of history, just three butterflies out of ten thousand – but its presence makes an enormous difference. Remove those three molecules, and we’d have no greenhouse effect; Earth would be a frozen snowball. But add three more, and the planet would become a sweltering hothouse. (At the moment, we’re actually at four butterflies.)

I’ve been learning one or two new things from each episode, and what I learned from this one is the surprisingly long time we’ve known that pumping carbon into the air could alter the climate. Svante Arrhenius predicted it as early as 1896, and scientists throughout the 20th century confirmed and extended his work – including Carl Sagan, who was one of the first to hypothesize that Venus was boiling hot and that the greenhouse effect was the reason why.

But what was once a prediction has become an accelerating reality. The amount of carbon we’re pumping into the air is the equivalent of a new White Cliffs of Dover each year, a point underscored by a visual of the cliffs rising like an express elevator. We also saw the famous “hockey stick” graph, as well as scenes of glaciers and permafrost melting in the Arctic, a sight which always fills me with dread. The thawing poles, invisible to most of us who live at lower latitudes, are a scream of warning that climate change is already happening at a rate that outstrips some of our grimmest predictions.

This episode addressed climate-denialist arguments in much more detail than previous outings, and did a good job of dismantling them. It explained how we know that global warming isn’t being caused by the sun or by volcanoes, as well as the difference between weather and climate: the former is short-term and chaotic, whereas the latter is long-term and predictable. As Tyson said, global warming isn’t even especially complicated science. It’s basic physics, a simple matter of bookkeeping for the planet’s energy budget.

But as bleak as our situation seems, all hope isn’t lost. Humanity once confronted an equally serious crisis, namely the Cold War and the nuclear arms race (exemplified by the USSR’s Tsar Bomba test). In the midst of this apocalyptic standoff, the moon landing was conceived as a demonstration of the power and precision of American rocketry. But though it was born of militarism and nationalism, it gave us a vision that transcended these: the unity, beauty and fragility of the blue world where we all live, “one earth, indivisible”.

We can escape doom again, and it’s not as if we don’t have the tools. In two brief historical segments, the episode pointed out that solar energy has been recognized as a viable power source since the beginning of the Industrial Revolution. We were led astray by cheap fossil fuel, but now, on the brink of climate disaster, we’re rediscovering its potential. As Cosmos again reminded us, the sun and the wind provide more energy than we could ever need. The obstacle isn’t the technology, but the political will to use it.

In a closing visual, this episode hinted at what Earth could look like in the future if we take heed: the Sahara flushed with green, irrigated by canals striped with solar panels; cities turned into living parks, with vast skyscrapers carpeted by green roofs. Surprisingly, one thing this episode didn’t dwell on were the consequences if we don’t act and global warming continues unchecked: rising seas, fiercer and more destructive storms, more droughts and floods, famines, mass migrations and wars fought over water and land.

Showing these possible futures side-by-side would have been a powerful way to dramatize the choice we face. The danger is looming, threatening to overwhelm us; but imminent disaster has often been the goad that unites humanity and inspires us to our greatest heights of achievement. Averting catastrophe, at this point, will take a collective effort that will dwarf the moon shot. But if we succeed, it will truly be our finest hour.

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DAYLIGHT ATHEISM Adam Lee is an atheist author and speaker from New York City. His previously published books include "Daylight Atheism," "Meta: On God, the Big Questions, and the Just City," and most...