So what is the scientific consensus about the answers to the key questions concerning global warming?

The British magazine New Scientist gives a review of the state of affairs concerning climate change, along with a handy summary sheet of the main points, and the Intergovernmental Panel on Climate Change (IPCC) report (thanks to Brian Gray of the Kelvin Smith Library who runs the blog e³ Information Overload for the link) provides more detailed information. Here are some tentative answers to the five key questions I raised in a previous post.

1. Is warming occurring? In other words, are average temperatures rising with time?

Here we have to distinguish between the more recent period (starting in 1861) when we have direct measurements of temperature and the prior periods, for which we have to infer temperatures using proxy measures such as using tree rings or bubbles trapped in ice cores that date back 750,000 years.

For the recent past, the IPCC report says that “The global average surface temperature has increased by 0.6 ± 0.2°C since the late 19th century”.

For the period prior to that, the report says “It is likely that the rate and duration of the warming of the 20th century is larger than any other time during the last 1,000 years. The 1990s are likely to have been the warmest decade of the millennium in the Northern Hemisphere, and 1998 is likely to have been the warmest year.”
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In the previous post, I discussed how after a paradigm is adopted, scientists tend to communicate only with each other. They are now freed from the need to explain and justify the basic premises of the field to a lay public, and no longer have to make a political case to justify what they are doing. This results in them developing a more technical, insider language and jargon that is opaque to nonscientists, and the technical paper addressed to similarly trained scientists and published in specialized journals becomes the chief means of communication.
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The need to take global warming seriously is not slam-dunk obvious to most people. In my own case, over time I have slowly became convinced that there was an emerging consensus among scientists studying the issue that planetary warming was a serious matter. Like most people, I do not have the time or the expertise to have studied the question in detail, but I have enough respect for the scientific process and the way that scientists make collective judgments as a community that when I see a scientific consensus emerging on anything, I tend to take it seriously. In fact the global warming issue is a great example of seeing, before our very eyes, a transition in science from a pre-paradigmatic state to a paradigmatic state.
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Is there a scientific consensus on global warming? Naomi Oreskes from the Department of History and Science Studies Program, University of California at San Diego, thinks so. She published a study in the journal Science (December 3, 2004, volume 306, p. 1686) which argued that the scientific community had arrived at a consensus position on “anthropogenic climate change.” i.e. that global warming was occurring, and that “Human activities . . . are modifying the concentration of atmospheric constituents . . . that absorb or scatter radiant energy. . . . [M]ost of the observed warming over the last 50 years is likely to have been due to the increase in greenhouse gas concentrations”.
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To understand the science behind global warming, it may be helpful to look at a simplified version of the science behind it.

Consider two objects, one that is luminous (i.e., an object that we can see without the aid of a light source) and another that is not luminous. Examples of luminous objects are the Sun (which generates energy due to nuclear reactions within it and sends a lot of that energy out as light) or a light bulb (that converts electrical energy into light energy). Examples of non-luminous objects are the Earth or a person in a room. The energy radiated by the luminous source spreads out in all directions and some of it will fall on the non-luminous object.

What is important to understand is that even what looks like a non-luminous object also radiates energy into space. In fact every object radiates energy. So in a sense, every object is ‘luminous’ in the sense that it sends out energy, but we usually reserve that term for objects that emit visible light. Not all radiated energy is visible. A human being radiates energy at a rate of about 500 watts, or the equivalent of five 100 watt bulbs, but the reason we do not “see” the radiation energy emitted by people is due to it being outside the visible range

The rate of energy emission of an object radiates depends to a large extent on its temperature (it actually goes as the fourth power of the temperature) and the nature of its surface (such as color, texture, material). So just as the Sun radiates energy into space, so does the Earth, except that the Sun’s radiation is much greater since it is at a much higher temperature.

The important thing about global warming is understanding what happens when the energy radiated by a luminous source (say the Sun) falls upon a non-luminous object (say the Earth). Part of it is immediately reflected back into space, and does not affect the temperature of the Earth. But the rest is absorbed by the Earth and, in the absence of anything else happening, will tend to cause the Earth’s temperature to rise. The relative amounts of the Sun’s energy that are absorbed and reflected by the Earth depends on the nature of the Earth’s surface. (As an example, a person in a room absorbs energy from the surroundings at a rate of about 400 watts, thus adding a person to a room is the net heat equivalent of turning on a 100 watt bulb.)

But as the temperature of the object rises due to it absorbing energy, the amount it radiates out again also increases, and at some point the object reaches equilibrium, which occurs when the energy absorbed by it from outside equals the energy it radiates away. Once an object reaches this state of thermal equilibrium, its temperature stays steady.

If for some reason we alter the ratio of energy absorbed by the Earth to the energy reflected, then the state of equilibrium is disturbed and the Earth’s temperature will shift to a new equilibrium temperature. If relatively more energy gets absorbed, then the equilibrium temperature will rise until the energy radiated again becomes equal to the energy absorbed. Conversely, if relatively more energy now gets reflected, then the equilibrium temperature will drop, i.e., the Earth will cool. The people warning of global warming argue that human activity is causing the former situation and they say that the reason for this is that we are changing the nature of the Earth’s surface, especially its atmosphere.

To understand what is happening at the Earth’s surface and atmosphere, we need to understand something about the energy radiated by the Sun. This comes largely in the form of “electromagnetic energy.” This is an umbrella term that encompasses X-rays, ultraviolet, light waves, infrared, microwaves, radio waves, etc. All these types of radiation are identical except for one single factor, which is called the wavelength of the radiation. The items in the list differ only in their wavelengths, with X-rays having the smallest wavelength and radio waves having the longest. (Similarly, all colors of visible light are also identical except for the wavelength, which increases as you go from blue to green to yellow to red.)

When this broad range of electromagnetic radiation from the Sun hits the Earth’s atmosphere, almost all of it, except the visible light portion, gets absorbed by the atoms and molecules in the atmosphere and does not reach us on the ground. Of the portion that does reach the ground, some of it gets directly reflected unchanged and escapes back into space. The remainder gets absorbed by the ground. It is the energy that is absorbed by the ground that is the source of concern.

Recall that the Earth, like any object, also radiates energy away. But since the temperature of the Earth is different from the temperature of the Sun, the distribution of the wavelengths in the energy radiated by the Earth is different from the distribution that we receive from the Sun (although the total energy involved is the same in both cases for an object in equilibrium). This affects how much is absorbed by the atmosphere as it passes through it. Some of the Earth’s radiation will get absorbed by the gases in the atmosphere (i.e., is trapped), while the rest passes through and goes off into space.

This is a crucial point. If the gases in the atmosphere change significantly, then you can change the relative amounts of the Earth’s radiated energy that escapes into space and the amount that is trapped by the atmosphere . The so-called ‘greenhouse gases’ (carbon dioxide, water vapor, methane, nitrous oxide, and others) are those that are very good at absorbing the energy at the wavelengths radiated by the Earth, preventing them from escaping into space.

Global warming scientists argue that human activity is increasing the concentration of greenhouse gases (especially carbon dioxide) in the atmosphere. Hence more of the energy radiated by the Earth is being absorbed and less of the energy is escaping into space. Note that the incoming visible light from the Sun is not affected much by the concentrations of greenhouse gases since they are at a different wavelength, and the greenhouse gases do not absorb them as much. As a result of this increase in the absorption levels of the outbound radiation, the equilibrium temperature of the Earth will rise.

At this point, there are various scenarios that can unfold. One is that we arrive at a new and higher but stable equilibrium temperature. If the change in equilibrium temperature is small, the consequences might not be too disastrous, although there will be some adverse effects such as some temperature-sensitive organisms (such as coral reefs) becoming destroyed or some species going extinct if they cannot evolve mechanisms to cope. If the change is large, then there could be massive floods and droughts and other catastrophes.

The worst case scenario is a kind of runaway effect, where a rise in temperature results in effects that cause an even more rapid rise in temperature and so on, in a series of cascading effects.

Some argue that we are already seeing some signs of runaway effects, and point to the melting of the polar ice caps and the general decrease in glaciers and snow coverage worldwide. Snow is white and thus reflects back unchanged into space almost all the sunlight that hits it at the Earth’s surface. When this snow melts and becomes water, not only is the amount of reflected energy decreased but water absorbs light energy. Hence the major loss of snow cover (apart from adverse environmental and ecological consequences) has a major effect on the reflection/absorption balance of the Earth, shifting it towards greater absorption. So more energy is absorbed by the Earth, resulting in even greater warming, resulting in further snow loss, and so on.

Another possible runaway factor is the amount of green cover. On balance, plants, because of photosynthesis, tend on average to be net absorbers of carbon dioxide and emitters of oxygen. Thus they reduce one of the greenhouse gases. If global warming results in less green cover of the Earth (say caused by prolonged droughts), then that would result in more greenhouse gases remaining in the atmosphere and causing yet more warming and more droughts. Human activity such as deforestation can accelerate this process.

Those are the basic elements of the science underlying global warming and the factors that go into building the models that try to predict long term climate change.

Next: The emerging scientific consensus over global warming.

POST SCRIPT: Colbert takes media apart again

As you may recall, the mainstream media did not take kindly to Stephen Colbert’s demolishing them at the White House Correspondents Association Dinner. Now he takes them apart again.

Understanding global climate concerns is not easy because it is a complex issue which involves many factors and theories, is based on data that span millennia and is not easy to extract, involves sophisticated theories and computer modeling, and requires long chains of inferential reasoning to arrive at conclusions. Compared to it, evolution, that other anathema of Bush and his anti-science Christian base, is a model of clarity.

At least with evolution, the progression shows a clear pattern, with life evolving from simple single cell organisms to the wide array of complex multi-cell systems we see today. If we started discovering anomalous organisms that seem to violate that temporal ordering, that would require a major restructuring of evolutionary theory.
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It is undoubtedly true that, while the increasing level of warfare in the Middle East in the immediate issue of concern, the question of global warning is the preeminent long term issue facing the planet today. It represents one of the rare situations when the health of the entire planet is at stake. The only other thing that has similar global consequences is an all-out nuclear war between major nuclear powers since that could also unleash an atmospheric catastrophe that could destroy the planet.

But while we can avoid a nuclear winter by simply doing nothing, i.e. not using the weapons, global warming is an issue where doing nothing is the problem. A strong case has been made that if we continue on the present course, the planet is going to suffer irrevocable harm, changing its climate and weather patterns in ways that will dramatically affect our lives, if not actually destroy them.

One would think that global warming is one scientific question where politics would play a minor role, and where the debate would be based on purely scientific evidence and judgments. Unlike issues like stem cell research and cloning where the scientific questions have to contend with religion-based arguments, as near as I can tell the Bible, Koran, and other religious texts are pretty much agnostic (so to speak) on the issue of whether global warming is something that god has strong views on. While god has a lot to say about things like the proper ways to sacrifice animals or how sinners should be put to death, he seems to not be concerned about the weather, expect for using it as a tactical weapon, like unleashing the occasional deluge to drown everyone but Noah and his family or creating a storm to chastise his prophet Jonah.

Hence it is surprising that some people (including the Bush administration) perceive the case being made that global warming is a serious problem as some kind of ‘liberal’ plot, tarring the proponents of the idea that global warming is real and serious as political enemies, seeking to somehow destroy truth, justice, and the American way. Glenn Greenwald argues that this is the standard mode of operation of the Bush administration, saying “What excites, enlivens, and drives Bush followers is the identification of the Enemy followed by swarming, rabid attacks on it.”

Once that bugle call of politics sounded, Bush devotees dutifully fell into line. They know the script and exactly what they must do and have rallied to the cause, trying to discredit the scientific case and the scientists behind it, arguing that the whole global warming thing is a fabricated crisis, with nothing more to be worried about than if we were encountering just a warm summer’s day. Senator James Inhofe (R-OK) says “With all of the hysteria, all of the fear, all of the phony science, could it be that man-made global warming is the greatest hoax ever perpetrated on the American people? It sure sounds like it.” And this man is the Chair of the Senate’s Committee on 
Environment and Public Works.

The administration and its supporters have gone to surprisingly extreme methods to suppress alarms about climate change, such as changing the wording of reports by government scientists in order to play down the threat of global warming and muzzling government climate experts, in order to prevent information from getting to the public.

Take another example in which the administration has sought to divert government’s scientist’s focus from global warming:

From 2002 until this year, NASA’s mission statement, prominently featured in its budget and planning documents, read: “To understand and protect our home planet; to explore the universe and search for life; to inspire the next generation of explorers. . .as only NASA can.”

In early February, the statement was quietly altered, with the phrase “to understand and protect our home planet” deleted. In this year’s budget and planning documents, the agency’s mission is “to pioneer the future in space exploration, scientific discovery and aeronautics research.”

David E. Steitz, a spokesman for the National Aeronautics and Space Administration, said the aim was to square the statement with President Bush’s goal of pursuing human spaceflight to the Moon and Mars.

But the change comes as an unwelcome surprise to many NASA scientists, who say the “understand and protect” phrase was not merely window dressing but actively influenced the shaping and execution of research priorities. Without it, these scientists say, there will be far less incentive to pursue projects to improve understanding of terrestrial problems like climate change caused by greenhouse gas emissions.

“We refer to the mission statement in all our research proposals that go out for peer review, whenever we have strategy meetings,” said Philip B. Russell, a 25-year NASA veteran who is an atmospheric chemist at the Ames Research Center in Moffett Field, Calif. “As civil servants, we’re paid to carry out NASA’s mission. When there was that very easy-to-understand statement that our job is to protect the planet, that made it much easier to justify this kind of work.”

Several NASA researchers said they were upset that the change was made at NASA headquarters without consulting the agency’s 19,000 employees or informing them ahead of time.
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The “understand and protect” phrase was cited repeatedly by James E. Hansen, a climate scientist at NASA who said publicly last winter that he was being threatened by political appointees for speaking out about the dangers posed by greenhouse gas emissions.

The attempts to downplay the extent of the problem, divert attention away from actions to study and remedy it, and distort the science behind the global warming issue has been helped by the fact that although the consensus conclusions of the scientific community are pretty straightforward (that global warming is occurring, it is largely caused by human activity, and that we need to take steps to reverse it or face disastrous consequences), the actual science behind it is complicated. This enables those who wish to blur the issue to find ways to cast doubt on that scientific consensus.

Next: Understanding the problem