‘Cosmos’ recap: Climate change is explained in ‘The World Set Free’


Is it getting hot in here? In what is likely to prove one of its most controversial episodes yet, this week’s “Cosmos” lays out the powerful scientific case for climate change, framed within a tale of two planets: Venus and Earth.

Venus was not much different from Earth back in the earliest days of the solar system, with vast oceans and an atmosphere potentially friendly to life. Visit Venus today, however, and you’ll find that its once abundant oceans have long since evaporated away because of the broiling temperatures -- hot enough to melt lead, and certainly hot enough to destroy Venera 13, a Soviet space probe that landed on the surface of Venus in 1982. Thanks to on-board cooling systems, the craft stayed operational for a couple of hours — long enough to take pictures of the planet’s surface and beam them back to Earth, before the searing heat fried the electronics.

What happened to Venus to turn it from a nascent paradise into an uninhabitable hell? That fiery temperature isn’t because the planet is 30% closer to the sun. As host Neil deGrasse Tyson points out, Venus is covered by thick sulfuric clouds, which keep much of the sun’s light from ever reaching the planet. So why isn’t Venus a block of ice? A little light gets through — but it can’t back out again because there is so much carbon dioxide in the atmosphere. So that energy never escaped and Venus got hotter and hotter. It’s called the runaway greenhouse effect.


We can learn much from Venus about the possible fate of our own pretty blue planet. True, the catastrophic climate change on Venus had nothing to do with mankind. “Nature can destroy an environment without any help from intelligent of life,” says Tyson. But the same fundamental science applies to Earth.

Earth benefited from a milder version of the greenhouse effect. Whereas most of the Venusian CO2 is in gaseous form in the atmosphere, our planet developed an efficient conversion cycle through which carbon could be stored in coral reefs, or limestone rock, — like the stunning White Cliffs of Dover on the coast of England.

So there were only trace amounts of CO2 in our atmosphere: less than three molecules in 10,000. If there were none, Earth would be a ball of ice; too much, and Earth would look like Venus. We’re in the “Goldilocks zone” when it comes to CO2 levels, but it only takes a tiny shift in the balance to tip us into a runaway greenhouse effect — and that is precisely where we are heading.

We don’t think of planets as living organisms, but Tyson insists that the Earth “breathes” with the seasons, taking in CO2 (via trees and other vegetation) in the spring and “exhaling” it back into the atmosphere in the winter. (The seasons are reversed in the Southern Hemisphere.) So there’s a natural fluctuation to CO2 levels in the atmosphere.

An oceanographer named Charles David Keeling was the first to notice this when he measured how much CO2 was in the atmosphere. And he made another startling discovery: an alarming sharp rise in the overall levels since the Industrial Age, when humans started burning coal, oil and gas for energy. (It’s now known as the “Keeling Curve.”) We can see this in ice core samples taken in Antarctica and Greenland, giving us a detailed “diary” of Earth’s atmospheric history. Aside from seasonal fluctuations, until the 19th century, CO2 levels hadn’t fluctuated by more than 1% over millions of years.

One by one, Tyson sets up the objections touted by those who deny the reality of climate change, and knocks them down with scientific facts. No, it has nothing to do with volcanic activity. True, Mt. Etna in Sicily belches millions of tons of CO2 into the atmosphere every time it erupts, but human use of fossil fuels adds 30 billion tons each year — too much for Earth to absorb and store. (And yes, we can tell the difference, because CO2 from volcanic activity has a distinct chemical signature that we can easily measure.)

He also makes a clear distinction between weather and climate. You hear the jokes every time there’s a cold spell in winter: “So much for global warming, ha ha ha!” For the record: Weather is how the atmosphere behaves day to day, which is a highly chaotic system and impossible to predict beyond a few days because there are so many variables that can influence weather patterns. Climate is the long-term average of weather patterns tracked over many years, and far more stable.

Tyson compares climate to the straight path his footprints make on the beach; weather is the dog walking alongside him on a leash, wandering to and fro but always within the constraints of the leash. When it comes to climate change, “Keep your eye on the man, not the dog,” he advises.

All told, “It’s a pretty tight case — our fingerprints are all over this thing,” Tyson concludes. Carl Sagan gave the same warning when the original Cosmos aired. And yet even a 98% consensus among climate scientists that this is real and that it’s man-made isn’t sufficient to lay the pseudo-”controversy” to rest.


Why? Chances are, how you respond to this episode will dovetail neatly with how you self-identify on the political spectrum. Several studies have shown a pronounced “backfire effect” in response to countering unfounded political opinions with factual evidence to the contrary. Rather than adjusting their opinions to be more factually correct, many people double down on their preexisting beliefs. They will not be swayed by facts, finding all manner of rationalizations to ignore the overwhelming evidence.

Here’s the thing: Nature doesn’t care about your politics, or what you want to be true. It just does its thing according to the well-established rules described by science. We ignore reality at our peril.

The sharp rise since the late 19th century means that the average global temperature is rising, with some pretty devastating consequences for our environment. Melting ice caps, rising sea levels, heat waves, record droughts, severe storms, mass extinctions — this is the legacy we’re leaving to future generations, unless we find the collective will to do something about it and become better stewards of our planetary home.

Tyson specifically mentions two promising renewable energy sources — wind turbines and solar power — that could help reverse the alarming upward trend in CO2 levels in the atmosphere.

We’ve been at the solar crossroads before. At the Universal Exhibition in Paris in 1878, Augustin Mouchot demonstrated a solar-power engine capable of making ice by converting the sun’s rays into mechanical steam power. He won a gold medal and everything. But this coincided with cheap coal — so cheap his solar device couldn’t compete economically. He ultimately lost his funding.

We were at a crossroads again in 1913, when the American inventor Frank Shuman built a solar array to power steam engines in Egypt, with an eye toward using it to irrigate the desert. But the market for cheap petroleum exploded, and the outbreak of World War I led to his solar arrays being recycled into weapons. His invention didn’t go anywhere, either.

We’re an adaptive species; it’s what’s enabled us to survive. But the climate clock is ticking. Quite frankly, we can’t afford to wait another 100 years; the time to invest heavily in renewable energy is now. Only by facing the facts can we find a solution and avoid bringing about our own mass extinction.