Storms of My Grandchildren (3 page)

Some who say the sun plays a larger role in climate change than carbon dioxide or other greenhouse gases hypothesize that there must be other indirect effects that magnify the small measured variations of solar brightness. The most common hypothesis is an almost Rube Goldberg concoction: the sun altering cosmic rays, which then alter cloud condensation nuclei, which alter cloud cover, which alters absorbed sunlight, which alters climate. However, there is no meaningful evidence supporting a large indirect amplification. The small cyclic component of global temperature that is extracted from statistical analyses of observed global temperature is consistent with a solar forcing of 0.2 to 0.3 watts. Possible errors in extracting the cyclic temperature response allow, at most, amplification of the solar forcing by a factor of two, which still leaves the cyclic solar forcing much smaller than the greenhouse gas forcing.

A bigger question about the sun remains: How large are solar variations on the century timescale? The 1750–2000 solar forcing estimated in figure 1 is based on research of solar experts, especially Judith Lean and Claus Fröhlich, who used indirect (“proxy”) indicators of solar activity, such as sunspots. They assume that the relation between solar activity and solar brightness observed in the past few decades is the same as it was a few hundred years ago. That leads to the conclusion that recent solar forcing is a few tenths of a watt greater than it was in the eighteenth century. The uncertainty, however, is large, as figure 1 indicates.

The other known natural climate forcing mechanism, volcanoes, probably worked in the same sense as the sun over the interval from the mid-eighteenth to the mid-twentieth centuries. That is because the available data, meager as they are, suggest that volcanic activity was greater in the eighteenth century than in the twentieth century. Actually, between 1963 and 1991 three large volcanoes (Mount Agung, El Chichón, and Mount Pinatubo) erupted, a degree of volcanic activity that would have been at least comparable to that in the eighteenth century. However, when people compare eighteenth- and twentieth-century climates to examine the effects of natural climate forcings, they usually exclude the last few decades of the twentieth century because, by that time, the human-made greenhouse gas forcing was so large that it eclipsed the effects of even three large volcanic eruptions; whereas up through the middle of the twentieth century, the net human-made climate forcing was rather small.

The increase of climate forcing in the mid-twentieth century due to the changing level of volcanic activity, relative to the eighteenth century, is estimated as 0.15 watts, with an uncertainty of about 0.1 watts. Thus the net change of natural climate forcings over the past two centuries was possibly as much as + 0.5 watts. This would be at least as large as the human-made climate forcing up through the middle of the twentieth century. Therefore natural forcings are a good candidate for explaining, or helping to explain, observed climate change up to the mid-twentieth century.

Climate change between the eighteenth and twentieth centuries was noticeable. The eighteenth century fell within the Little Ice Age, which is sometimes described as taking place from 1600 to 1850 and sometimes from 1250 to 1850. Climate fluctuated from year to year and decade to decade, but changes between the eighteenth and twentieth centuries were significant. In 1780, for example, soldiers in the American Revolution could drag cannons across the frozen New York harbor from Manhattan to Staten Island. The River Thames frequently froze over in the 1700s, and people held ice fairs on it. The twentieth century was too warm for such events to be possible.

Yet how much warmer was the first half of the twentieth century relative to the Little Ice Age? The cooling during the Little Ice Age, averaged over the planet and over the seasons, was probably less than one-half degree Celsius. Our knowledge of both the climate forcing over the past millennium and the climate change are too imprecise to allow empirical evaluation of climate sensitivity.

In contrast, the climate change between modern conditions and the last Major Ice Age, twenty thousand years ago, was an order of magnitude larger. An ice sheet more than a mile thick covered present-day Canada and northern parts of the United States, including Seattle, Minneapolis, and New York City. Another ice sheet covered Europe. The global average temperature was 5 degrees Celsius (9 degrees Fahrenheit) colder than today’s. The climate forcing mechanisms that maintained the temperature change were also an order of magnitude larger than the forcings in the last two centuries caused by the sun and volcanoes. The glacial-to-interglacial climate and forcing mechanisms are known well enough to accurately define climate sensitivity (as discussed in chapter 3).

What is clear is that human-made climate forcings added in just the past several decades already dwarf the natural forcings associated with the Little Ice Age. Carbon dioxide increased from 280 parts per million (ppm; thus 0.028 percent of atmospheric molecules) in 1750 to 370 ppm in 2000 (and to 387 ppm in 2009). The impact of this CO2 change on Earth’s radiation balance can be calculated accurately, with an uncertainty of less than 15 percent. The climate forcing due to the 1750–2000 CO2 increase is about 1.5 watts. Other human-caused changes, such as adding methane, nitrous oxide, chlorofluorocarbons (CFCs), and ozone to the atmosphere, make the total greenhouse gas forcing about 3 watts.

I had a small 1-watt Christmas tree bulb in my pocket at the Task Force meeting, which I pulled out during my presentation, causing some eyebrows to raise in curiosity. I explained that the net effect of human-made climate forcings was equivalent to having two of those bulbs burning night and day over every square meter of Earth’s surface.

I mentioned that in some sense the forcing by two 1-watt bulbs is small—it cannot stop the wind or alter an ongoing weather fluctuation. Yet if it is left in place for decades and centuries, long enough to allow the ocean temperature to fully respond, it is a huge forcing.

Colin Powell, who had returned from his phone call in time for my presentation, asked about the “black soot,” or black carbon aerosols—a topic I had hoped would be raised. Black soot, unlike sulfates and other reflective aerosols, absorbs sunlight and thus can cause warming. It is also among the most dangerous of aerosols to human health. Black soot is produced by diesel engines, household coal burning, and stoves that burn field residue or animal waste. It is especially abundant in India, China, and other developing countries.

The point I wanted to make was that a focus on air pollution has practical benefits that unite the interests of developed and developing countries. I had included in my handout a paper that four colleagues and I had published in 2000. We advocated an “alternative scenario” for twenty-first-century climate forcings, alternative to the business-as-usual scenarios studied by the Intergovernmental Panel on Climate Change.

Our alternative scenario emphasized the merits of reducing health-damaging air pollutants, especially black soot, low-level ozone, and methane. We argued that carbon dioxide emissions also would need to be slowly reduced, with atmospheric carbon dioxide kept to a maximum of about 450 ppm (I now realize that carbon dioxide will need to be reduced even further, to 350 ppm, at most). If both of those goals were accomplished, additional global warming, beyond that in 2000, would be less than 1 degree Celsius (1.8 degrees Fahrenheit)—much less than that in IPCC scenarios. Climate effects may still be significant, but they would be far less damaging.

We moved on to Ron’s presentation on climate modeling. As Dan had seemed to anticipate, the sledding became difficult as we got into the complexities of climate modeling, the many components that make up the models, and the uncertainties. Some eyes began to glaze over in regard to the complexities of cloud modeling. Cheney interrupted, saying that the topic was important but another session would need to be scheduled to complete it.

Our meeting ended with a curious juxtaposition of comments about the next meeting by O’Neill and Cheney. O’Neill noted that all the present speakers were convinced of the reality of concerns about human-made global warming. He suggested that the next meeting include a global warming contrarian (disbeliever). His rationale was that the Task Force should not be criticized for listening to only one perspective. The rationale might have been sound, but unless there was independent expert arbitration, such as by the National Academy of Sciences, there was a risk that the Task Force would end up simply being perplexed.

Cheney then read statements from the abstract of our alternative scenario paper about the importance of climate forcings other than carbon dioxide. He concluded that the Task Force should hear more from me. The vice president, no doubt, was attracted by our emphasis on less well-known climate forcings, because most of those forcings had sources other than fossil fuels. His specific interest made me uncomfortable, because his choice of speaker seemed to be based on who would deliver an answer that he wanted to hear. That is pretty much the opposite of the scientific method. In science, you want to examine evidence that seems to disagree with your preliminary interpretation. You must evaluate contradictory evidence to make sure that you are not fooling yourself.

If the vice president had read our entire paper carefully, he would have realized that we also called for much less fossil fuel burning than in IPCC scenarios. Nevertheless, being an eternal optimist (what else can be effective?), I welcomed the chance to appear before the Task Force again. My aim would be to clarify that reducing carbon dioxide emissions, as well as air pollutants, was needed to stabilize climate.

As fate had it, three days before the next Task Force meeting, a Chinese fighter jet bumped a U.S. Navy reconnaissance plane, forcing it and its twenty-four crew members to make an emergency landing in China. Because of diplomatic efforts to recover the crew and plane, both the vice president and secretary of state were absent from the second meeting, held at the Environmental Protection Agency headquarters.

They did not miss much.

Richard Lindzen of the Massachusetts Institute of Technology and I were the presenters at the second meeting. Lindzen is the dean of global warming contrarians, the one who is most articulate and has the most impressive scholarly credentials. He was elected to the National Academy of Sciences at a tender age, primarily as a result of brilliant mathematical analyses of atmospheric dynamics.

I knew what I would be up against. In a situation like this, presentation and style are as important as substance. Lindzen is soft-spoken but has an authoritative air; he never loses his cool and is always in complete control. He and other contrarians tend to act like lawyers defending a client, in my opinion, presenting only arguments that favor their client. This is in direct contradiction to my favorite description of the scientific method, by Richard Feynman: “The only way to have real success in science…is to describe the evidence very carefully without regard to the way you feel it should be. If you have a theory, you must try to explain what’s good about it and what’s bad about it equally. In science you learn a kind of standard integrity and honesty.”

The scientific method, in one sense, is a handicap in a debate before a nonscientist audience. It works great for advancing knowledge, but to the public it can seem wishy-washy and confounding: “on the one hand, this; on the other hand, that.” The difference between scientist-style and lawyer-style tends to favor the contrarian in a discussion before an audience that is not expert in the science.

I long ago realized that the global warming “debate,” in the public mind, would be long-running. I also noted that contrarians kept changing their arguments as the real-world evidence for global warming continued to strengthen, conveniently forgetting prior statements that were proven wrong. For that reason, when I publicly debated Lindzen in 1998, and contrarian Pat Michaels a few weeks later, I decided that the best approach was to make a table of our basic differences.

My plan for the second Task Force meeting was to first summarize my conclusions from the first meeting and discuss the relevance of the information for policy. Then I would deal with the contrarian perspective with a single chart, my “table of differences.” I brought a transparency of that table (a viewgraph—I was a holdout from PowerPoint for many years).

I started by again showing the climate forcings bar graph (figure 1) and drawing big circles around the bars representing methane (CH4), ozone, and black carbon aerosols (black soot). I noted that together these health-damaging air pollutants contributed as much climate forcing as carbon dioxide.