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Being an astrophysicist myself, most of the science isn’t new to me (some of it is even slightly outdated) and I enjoy the series mostly for the cultural references and historical context.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.

Now

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!


The sun wakes again

January 31, 2010


The astronomy department of the University of Amsterdam recently moved to a new building which will eventually house all science research of the UvA. One of the best things out of this is that the institute now has two brand new telescopes for educational purposes, one of which for looking at the sun. Last Monday the astronomy professor in charge of the two observation domes finished mounting the solar telescope and I took some pictures with my mobile phone of the image that it projects (it took me a while to get them off the phone and on the computer, I had some troubles with the Bluetooth settings of the phone)

The pictures show the image from the telescope as it is projected on a white screen mounted directly behind the telescope, taken on January 22nd. The white spot is the sun shining directly on the screen, the grey / yellow disc is the projection. The blurry edge around the disc is caused by the atmosphere in Amsterdam. The little black dot and the baby dots on the right in the disc are sunspots – the only visible sunspots on the entire sun! The professor was ecstatic that there was at least one proper sunspot, for he had set up an elaborate astronomy class elsewhere a week before and the students ended up disappointed because there wasn’t a single sunspot to be seen.

The sun has been extraordinarily quiescent the past years, even beyond the normal solar cycle. Which may be boring for astronomers, but from the perspective of climate science has been a relief. Although not much of a relief, for the past decade nevertheless still is the warmest decade on record. This record is likely to be broken by the following decade as the sun becomes active again. To quote p. 37 of my copy of The New Solar system (4th edition) which I bought approximately one solar cycle ago for an introductory astronomy class:

The sun becomes brighter overall as the number of sunspots on its surface increases, and vice versa. This seems counterintuitive, since sunspots are cooler than their surroundings. However, the sunspot cycle is accompanied by variations in magnetic activity, which create an increase in luminous output that exceeds the cooling effects of sunspots. Indeed, the entire spectrum of the Sun’s radiation varies in step with the 11-year cycle of solar magnetic activity.


The Copenhagen diagnosis

January 20, 2010

The big climate conference in Copenhagen last December has resulted in a disappointment. Although it can be argued that US president Obama is working very hard to address the climate issue and is making progress, Copenhagen came at a bad moment for the US administration.

Nevertheless, the stakes remain incredibly high. This becomes clear when one reads the Copenhagen Diagnosis, an update on the state of the science of global warming that has been issued by leading climate scientists, independently from the IPCC assessments that are issued every four years. Although the report has been made available already last December (obviously to coincide with the Copenhagen conference), I think it is important enough to call attention to even if I am a bit late to the party. It is freely available from www.copenhagendiagnosis.org. For the impatient, I have copied the Executive Summary below.

The most significant recent climate change findings are:

Surging greenhouse gas emissions: Global carbon dioxide emissions from fossil fuels in 2008 were 40% higher than those in 1990. Even if global emission rates are stabilized at present-day levels, just 20 more years of emissions would give a 25% probability that warming exceeds 2°C, even with zero emissions after 2030. Every year of delayed action increases the chances of exceeding 2°C warming.

Recent global temperatures demonstrate human-induced warming: Over the past 25 years temperatures have  increased at a rate of 0.19°C per decade, in very good agreement with predictions based on greenhouse gas increases. Even over the past ten years, despite a decrease in solar forcing, the trend continues to be one of warming. Natural, short-term fluctuations are occurring as usual, but there have been no significant changes in the underlying warming trend.

Acceleration of melting of ice-sheets, glaciers and ice-caps: A wide array of satellite and ice measurements now demonstrate beyond doubt that both the Greenland and Antarctic ice-sheets are losing mass at an increasing rate. Melting of glaciers and ice-caps in other parts of the world has also accelerated since 1990.

Rapid Arctic sea-ice decline: Summer-time melting of Arctic sea-ice has accelerated far beyond the expectations of climate models. The area of summertime sea-ice melt during 2007-2009 was about 40% less than the average prediction from IPCC AR4 climate models.

Current sea-level rise underestimated: Satellites show recent global average sea-level rise (3.4 mm/yr over the past 15 years) to be ~80% above past IPCC predictions. This acceleration in sea-level rise is consistent with a doubling in contribution from melting of glaciers, ice caps, and the Greenland and West-Antarctic ice-sheets.

Sea-level predictions revised: By 2100, global sea-level is likely to rise at least twice as much as projected by Working Group 1 of the IPCC AR4; for unmitigated emissions it may well exceed 1 meter. The upper limit has been estimated as ~ 2 meters sea level rise by 2100. Sea level will continue to rise for centuries after global temperatures have been stabilized, and several meters of sea level rise must be expected over the next few centuries.

Delay in action risks irreversible damage: Several vulnerable elements in the climate system (e.g. continental ice-sheets, Amazon rainforest, West African monsoon and others) could be pushed towards abrupt or irreversible change if warming continues in a business-as-usual way throughout this century. The risk of transgressing critical thresholds (“tipping points”) increases strongly with ongoing climate change. Thus waiting for higher levels of scientific certainty could mean that some tipping points will be crossed before they are recognized.

The turning point must come soon: If global warming is to be limited to a maximum of 2 °C above pre-industrial values, global emissions need to peak between 2015 and 2020 and then decline rapidly. To stabilize climate, a decarbonized global society –with near-zero emissions of CO2 and other long-lived greenhouse gases – needs to be reached well within this century. More specifically, the average annual per-capita emissions will have to shrink to well under 1 metric ton CO2 by 2050. This is 80-95% below the per-capita emissions in developed nations in 2000.

I highly recommend reading the report itself. It is only 64 pages, including clear graphs and a number of gorgeous pictures (and lots of citations of scientific papers for further reading, for those who share my luck of having internet access to peer-reviewed journals). It also very specifically addresses and debunks a number of layman arguments that have often been put forth against climate change (“CO2 increase historically trails temperature increase and therefore it still does now”, etc).

In my opinion the report is an example of scientific outreach at its best. The climate debate has become heavily politicized (the public debate, that is. Although there exists a fierce and lively scientific debate about the details, the genuinely scientific debate on the reality of man-made global warming is long over. The basics of man-made global warming have been firmly established using the same scientific principles that are found in other natural sciences, like my own field of astrophysics). Whatever climate scientists do, it will be held against them: if they don’t invest time and energy in outreach they will be painted as stuck in their ivory towers and out of touch, and if they do, they will be labelled activists. The Copenhagen diagnosis presents a very strong case that outreach from active climate scientists is crucial to the public conversation. And someone who tells a disturbing truth is not by definition an activist.