Global Warming: The Smoking Gun?

Last week's publication of a new climate modeling study (1) investigating the evidence for man-made climate change is destined to have more than the average impact on the global warming debate. The study's lead author, Dr. James Hansen, has been a central figure in global warming research and helped bring the issue into the public's consciousness with his congressional testimony in 1988.

The new study uses the Goddard Institute for Space Studies (GISS) computer climate model to simulate global climate over the last 120 years when forced with estimates of greenhouse gases, aerosols (both man-made and volcanic), and ozone depletion. The current formulation of the model, which has evolved over the years, produces a global average temperature history that looks remarkably like the thermometer measurements. The authors specifically emphasize the agreement between a slight warming of the oceans over the last ten years or so, and the radiative forcing that the model produces when the anthropogenic gases and aerosols are included.

Taking this agreement as evidence that the model has substantially correct physics, they further note that the radiative imbalance in the model as of the end of their simulation period (2003) is still substantial (0.85 watts per square meter). This suggests that, even if we could stop producing greenhouse gases right now, there is still significant warming in our future, which they estimate to be about 1 degree F. The warming would be necessary to eventually restore the ocean-atmosphere system to a state of radiative balance. While the atmosphere could, by itself, adjust in a matter of months to such an imbalance, it is the immense heat sink of the ocean that ends up taking many years to fully respond with warming.

Last week's TCS article on this new study noted that, even taking the study at face value, the amount of global warming the GISS model produces is now considerably less than what it used to be. Thus, one unstated conclusion of the new work could have been "global warming won't be as bad as previously thought". Instead, Dr. Hansen emphasizes the need to keep future warming below a relatively modest level, appealing to some research that has suggested that the climate system is unstable if pushed beyond a relatively small amount of warming.

A five-page write-up companion to the research paper was distributed to the climate research community that describes what Dr. Hansen believes are the implications of the new study. He makes it clear that the model's radiative imbalance constitutes "smoking gun" evidence of anthropogenic climate change. But instead of a "smoking gun", I would like to suggest that the new study really just presents one, internally consistent interpretation of what might be going on in the climate system.

The authors' interpretation of their model is indeed a possible one, but there are others as well. First of all, the model has been repeatedly "tuned" with various forcings in an attempt to explain the global temperature record of the last century. There is nothing inherently wrong with this strategy, but it must be kept in mind that how we think the climate system works is guided by the historical temperature record, and what we think has influenced it. Since we really don't understand how natural climate fluctuations (except for volcanic eruptions) influence that record, we are restricted to what we do understand: mankind's production of greenhouse gases and aerosol pollutants. The real climate signal we are interested in, a gradual warming from increasing greenhouse gas concentrations, is dominated by a single mode -- an upward trend. We also know that carbon dioxide concentrations have similarly increased. Does this prove cause and effect? The assumption has been that there have been no significant natural long-term independent changes in clouds, water vapor, precipitation efficiency, deep ocean heat storage, or a variety of other known (or unknown?) processes that could affect global temperatures in a similar manner.

For instance, what if recent warming of the oceans is more due to a slight decrease in low clouds than to increased trapping of infrared radiation by greenhouse gases? Or what if a temporary change in the rate of heat exchange with the deep ocean has caused the recent warming of the upper layers of the ocean? There are surely other possibilities as well.

Dr. Hansen's prediction that we will soon experience a year with globally averaged warmth greater than that of 1998 will be an interesting test of his current view of the human influence on climate.

So, what would constitute "smoking gun" evidence for human-induced global warming? I would like to suggest the following as an example of such evidence. We would have needed 50 to 100 years of accurate satellite observations (not model-based inferences) of the radiative components of the Earth's radiation budget: at least the amount of absorbed sunlight and the amount of emitted infrared radiation. It has been exceedingly difficult from the limited record of satellite measurements to extract a signal of radiation imbalance in the climate system (let alone diagnose what has caused it). Over the period of a sufficiently accurate satellite record, we would need to be able to measure an increasing imbalance between absorbed sunlight and Earth-emitted infrared radiation. Then, through additional global-scale measurements, we would need to be able to rule out natural changes in clouds, water vapor, deep ocean heat storage, and any other process that could explain some or the entire radiation imbalance.

Some believe that the recent global warmth is greater that it has been in the last 1,000 years, which by itself would be evidence for man-caused global warming. I personally don't have much faith in the indirect estimates of global temperatures before the twentieth century, but I agree that the current warmth is unlikely to be entirely natural in origin. The big question is, how much of it?

Of course, it will be a long time before we ever reach the state of knowledge that would meet my above test as smoking-gun evidence, and so policy decisions will have to be made (or not be made) without all of the answers. Thus it is imperative that all of the uncertainties are laid out on the table before decisions are made.

Of course, if reducing greenhouse gas emissions was easy or cost effective, it would have already been done. So until we develop energy technologies that either greatly reduce or eliminate the production of carbon dioxide, the stark fact is that there will be a human toll to mandated reductions. A few percent reduction from using more solar- and wind-generated power might make us feel good about our efforts, but it will have almost no effect on future global temperatures. Ultimately, the problem will be solved through energy technology research, which necessarily requires strong economies that can afford to fund that research, which in turn requires access to affordable energy now.

In summary, the recent study by Hansen et al. indeed presents one possible interpretation of the available evidence, but it is a very human-centric one that assumes that natural decadal- to century-scale climate fluctuations are not to blame for at least some part of what has been recently observed. Or, using the "smoking gun" metaphor, it isn't yet clear whether mankind is the perpetrator, Mother Nature is an accomplice, or vice versa.

Nevertheless, the study represents the kind of synthesizing science that is needed in order to better understand the extent to which mankind is influencing the climate system.

1. Hansen, J., et al., 2005: Earth's Energy Imbalance: Confirmation and Implications. Science Magazine, 28 April.

Here's my forecast for today and tonight.

Decreasing cloudiness. Scattered rain showers or snow showers in the morning. Highs in the lower 50s. West winds 5 to 15 mph. Chance of precipitation 30 percent.
Tonight
Partly cloudy. Areas of frost after midnight. Lows in the upper 20s. Southwest winds 10 to 15 mph.

If WW-II didn't cause the great man-made climate catastrophe, it isn't going to happen, period. I mean, there may be global warming, but man has nothing to do with it.

In WW-II, every oil facily accessible to the axis world became a bombing target, the entire Japanese and German navies and merchant marines were sunk, and the whole world was running full bore on leaded gas for six or seven years. Seventy Japanese cities were torched and it's hard to say whether the bomb damage or the industrial effort behind the American war effort caused more pollution. Pittsburgh became a city of perpetual night from the effort. A hundred aircraft carriers were built, the Iowa-class battleships, merchant ships and liberty ships in gigantic profusion along with all of the other large fleet ships needed to win the war effort, all made of steel. No effort of any sort was made to deal with the pollution all of this caused and it did not cause the great man-made eco catastrophe.

The whole idea of man causing "global warming" is BS pure and simple.

You guys seem to be making light of a serious situation. Granted we don't have the technology to answer all of the questions but even the skeptical author admits that at least some of the global warming is caused by man.

Seems to me that for the sake of our children and our children's children that we should be conservative and err on the side of caution.

Largely to me, on the East Coast it's been getting colder - or should I say, stabilizing (at least in MD/mid-Atlantic).

We had alot more snow back in the '70s, but now we don't get much altho lately we've had more snowfalls. Yet here I am in May still a bit too cold. I recall in 95-96 still wearing my big puffy coat to work in CT. In CT we had only 1 "hot" month - August. Then I noticed in MD, it's been largely just really HOT in August. Back in the '80s-, June thru Sept was HOT in MD. Consistently. In April alot of the time you could just wear an outfit and be just fine; no coat needed. Now we're getting colder.

The real question is not even "are we getting warmer" (BTW, the chicken-littles in the '70s were worrying about it getting colder), it is this.

WHAT IS SO TERRIBLE ABOUT THIS TINY OVERALL CLIMATE CHANGE OF 1 F?

Why should we care about 1 Fahrenheit over a century? What disaster is going to happen from that? And if it's such a mild change, isn't there an excellent chance a new trend will emerge and COOL it by 2 F? What calamity is going to happen over a couple degrees? These aren't even in Celsius degrees, for crying out loud!

Why should we care about 1 Fahrenheit over a century?

The author states that IF we stopped producing greenhouse gases we would get the 1 Fahrenheit change. But we are not going to stop producing greenhouse gases anytime soon so the climate change will be greater than 1 degree.

I know that anyone can finance a scientific study to prove whatever it is they want to prove. My impression is that the majority of scientists around the world think global warming is a very big deal or at least they want us to believe that they think it's a big deal. Why do you think so many countries signed on to the Kyoto protocol? Are they just misinformed or do they somehow stand to benefit from curbing greenhouse gas emissions?

Why? Cuz it allows Commies to carry out more of what they like - regulation, regulation, regulation - then punishment. Which puts every1 under some totalitarian thumb at some point. There are so many Commies in this world; it is not really dead and any1 who says so is a damned fool. Look at this country - half of us are commies whether they acknowledge it or not. This "environmental" BS (which, BTW, who ever used the word "environment" before the '90s?) is another way to try to leverage commie practices.

I don't give a @$%!@ what the world thinks. In the BEGINNING the Founders didn't care what the world thought - they were rebelling against what was the norm all over. The norm SUCKED. The norm still SUCKS. So I really don't give a @%^$ what those idiots think.

As for the 1 deg, I'm sorry, but I've heard 1 deg ferretted around a long time as the trend we are actually headed for. Maybe I'm wrong.

Regardless, who cares about 5 deg? What is it really going to do? How horrible is it going to be? NO1 ASKS MUCH LESS ANSWERS THAT QUESTION. I'd like to see something besides "the oceans will rise - and you'll lose your waterfront property". So what? It ain't a flood that's going to take it out instantly. It's gradual. People will have to adjust and pull up stakes. And it won't be necessary to do it instantly.

What other things will happen? What plants & animals will really suffer? And why is it so terrible compared to apparent climate changes over the entire history of the Earth?

What other things will happen? What plants & animals will really suffer? And why is it so terrible compared to apparent climate changes over the entire history of the Earth?

Well, insofar as the ice caps melt, it would raise ocean levels. This would be a possible threat to Miami, NYC & New Orleans. Remember, when ice melts, oceans tend to rise, since much water resides in frozen form on land masses (see Iceland/Greenland for examples of this)

BTW acknowledging this is not communist. Science lies independent of ideology. For instance, if a heart in beating in a fetus, no amount of spin will obviate this fact. Ditto if the earth is warming, this is something we have to face up to & examine the consequences. Good science is just trying to see the world as it is..

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