No global cooling in Cosmos

July 25, 2011

A while back I started watching the famous documentary series `Cosmos’ by Carl Sagan. The series is very good, although it might take you more than the first episode to appreciate that if you see it today -you’ll have to get past that voice, droning on like reverend Lovejoy from the Simpsons and that ridiculous spaceship that William Shatner wouldn’t be caught dead in. But after a while, Sagan’s voice-over improves and he all but abandons his spaceship to end up presenting a series of fascinating lectures, supported by (mostly) excellent multi-media support.

Global cooling?

Being an astrophysicist myself, most of the science isn’t new to me (some of it is even slightly outdated) and I enjoy the series mostly for the cultural references and historical context. But then something caught my eye in episode 4 when the discussion turned to climate change. You might remember the but in the seventies, it used to be global cooling! meme that has been spread vigorously by fossil-fuel industry funded stooges (e.g. here, unmasked here) or by pop science writers who are really not all that clever. The purpose of the meme is of course to obfuscate and to lead the non-expert to believe that scientific consensus on climate change has been swinging back and forth between wildly diverging opinions over the course of the past decades, thereby diminishing the impact of the current overwhelming consensus in the climate science community that global warming is real, occurring now and is man-made. The whole global cooling story has already been thoroughly debunked (e.g. here, here). Since Cosmos was originally broadcasted in 1980, closer to the global cooling craze than the global warming craze, had the former really existed, it is interesting to hear what Sagan has to tell us about global climate change, if only to as a reminder how scientific consensus actually did emerge over the past decades.

Cosmos, 1980

The destruction of trees and grasslands makes the surface of the Earth brighter. It reflects more sunlight back to space and cools our planet. After we discovered fire we began to incinerate forests intentionally to clear the land by a process called “slash and burn” agriculture. And today, forests and grasslands are being destroyed frivolously, carelessly by humans who are heedless of the beauty of our cousins the trees and ignorant of the possible climatic catastrophes which large-scale burning of forests may bring.

So is Sagan implying here that we should be afraid of global cooling? At least he gives us a concise description of the mechanism. (By the way, the reference to trees as cousins should not be read as some wishy-washy new-ageism, but as a reference to an earlier point in the series where the incredible similarities on chemical and DNA level across the different species were discussed).

The indiscriminate destruction of vegetation may alter the global climate in ways that no scientist can yet predict. It has already deadened large patches of the Earth’s life-supporting skin. And yet, we ravage the Earth at an accelerated pace as if it belonged to this one generation, as if it were ours to do with as we please. The Earth has mechanisms to cleanse itself, to neutralize the toxic substances in its system. But these mechanisms work|only up to a point. Beyond some critical threshold, they break down. The damage becomes irreversible. [..] The bright, sandy surface and dusty atmosphere of Mars reflect enough sunlight back to space to cool the planet freezing out all its water, locking it in a perpetual ice age.
Human activities brighten our landscape and our atmosphere.
Might this ultimately make an ice age here?

Although the specter of global cooling is indeed raised, so is the lack of scientific certainty and consensus… But what about the greenhouse effect and the state of climate science in 1980?

At the same time, we are releasing vast quantities of carbon dioxide, increasing the greenhouse effect. The Earth need not resemble Venus very closely for it to become barren and lifeless. It may not take much to destabilize the Earth’s climate to convert this heaven, our only home in the cosmos into a kind of hell. The study of the global climate, the sun’s influence, the comparison of the Earth with other worlds… These are subjects in their earliest stages of development. They are funded poorly and grudgingly. Meanwhile, we continue to load the Earth’s atmosphere with materials about whose long-term influence we are almost entirely ignorant.

As I said, no consensus. And rather than revile today’s state of climate science, for example as summarized in the IPCC reports, we should be impressed with how far we’ve come in only a few decades.

Cosmos, 1990

Already ten years after the first airing of Cosmos, climate science (as well as astronomy) had advanced considerably, and when the series was reissued in the early nineties, a brief update was appended to many episodes. Regarding climate change, a ten year older Carl Sagan now had the following to add:

Since this series was first broadcast the dangers of the increasing greenhouse effect have become much more clear. We burn fossil fuels, like coal and gas and petroleum, putting more carbon dioxide into the atmosphere and thereby heating the Earth. The hellish conditions on Venus are a reminder that this is serious business. Computer models that successfully explain the climates of other planets predict the deaths of forests, parched croplands, the flooding of coastal cities, environmental refugees, widespread disasters in the next century unless we change our ways.


The surface of Venus (from Cosmos episode 4)

Just to dwell on the obvious… Sagan’s future is today’s now. We currently are experiencing many of the gloomy predictions from twenty years ago. I wrote this in NYC during a record shattering heat wave across the U.S. 71% of Texas suffers from exceptional drought, its driest period there since 1895, with heat waves raging through many southern states… The worst drought in Somalia in 60 years… One fifth of Pakistan flooded last year… Enormous floods in China and Australia as well… a monster heat wave in Russia… a drop in September arctic ice volume from 10,000 cubic km in 1980 to 4,000 cubic km now. The list goes on and on… Sagan wouldn’t mince words were he to provide another update to Cosmos!