Unfortunately, we are living in a world in which positions taken for purely intellectual reasons can have political and thus real-world consequences, due to their interpretation and propagation in the blogosphere. Ignoring that fact is irresponsible.

But the awareness of black carbon’s role in climate change has come so recently that it was not even mentioned as a warming agent in the 2007 summary report by the Intergovernmental Panel on Climate Change that pronounced the evidence for global warming to be “unequivocal.” Mark Z. Jacobson, professor of environmental engineering at Stanford, said that the fact that black carbon was not included in international climate efforts was “bizarre,” but “partly reflects how new the idea is.” The United Nations is trying to figure out how to include black carbon in climate change programs, as is the federal government.

When I said I retained some skepticism about global warming, what I meant was that I was not sure we really knew everything there was to know about the problem. If this isn’t a perfect example I don’t know what is. Obviously, the impact here is to make the problem much worse! But are there things we don’t know about, that are not in our models, that might, just might, mean that it’s not as bad as we think? It’s the ultimate hubris to assert that we know everything…we simply don’t. We do know enough that we need to be very, very concerned and begin to take real action. The potential down side is quite bad.

serial catowner, I think you are wrong that scientific skepticism is paralyzing. Quite the opposite, it is (or should be) liberating, intellectually! I think you mean that it is politically paralyzing, because it gives deniers an excuse for inaction. But is that a poor argument against scientific skepticism.

To Neal J. King:
I do not understand what the time-scale has to do with the effect. What I would like to know is what is the power per square meter of energy received from Sun and how much is emmitted back, i.e. how much is retained, and how this value compares to 3.7 W/m^2 associated to CO2

Aleksandar Mikovic (78):

- The average incoming flux at the top of the atmosphere is about 343 W/m^2. In steady-state, the outgoing flux is 343 W/m^2: In steady-state, they have to balance. The 3.7 W/m^2 imbalance associated with a 2X in CO2 is therefore a bit over 1% of the incoming flux; to find the actual increase, note that the imbalance scales logarithmically with the CO2 concentration
- The point about time scale: If you invoke causes for the ice-ages to explain climate change in the last 150 years, you have to explain why those causes are suddenly creating changes on such a tiny time scale only now. To be more specific: The glacial changes are generally attributed to the Milankovitch variations in orbital parameters, rotational precession parameters, and motion of continents over the globe. Which of these do you think has shifted significantly in the last 150 years?
- By contrast, the amount by which atmospheric CO2 has increased in the last 150 years is now more than 35%.

Like many scientists, for a long time I found that skepticism was its own reward. You often get lucky and are regarded as a very smart person who figures out a new way to look at things. Usually the worst thing that can happen is that you’re as wrong as most people.

Eventually, though, I realized that skepticism isn’t a universal salve for the human condition. In fact, I consider this whole “I’m a scientist, so I must be skeptical” to be total baloney. Nobody walks around being skeptical of gravity, even though we know so little about it, just because they are a scientist.

A scientist needs to be skeptical when they’re doing science. They are, however, perfectly free to believe in God, get lost in Mozart, and love women or men that some of us might regard as ‘plain’.

And where better to apply the freedom of not being paralyzed by skepticism than in saving the planet? In the real world, the paralysis of doubt has to be accompanied by an estimate of the costs of inaction. Dally where those costs are zero, make a choice and try something where they are high.

And apply some of that skepticism to the idea that cranking out fewer Hummers will be an economic loss. Something seriously wrong with that line of thinking.

The effect, 3.7 W/m^2 per CO2 doubling, is significant enough to shift temperatures according to the best modeling.

The comparison with causes for glaciation cycles (Milankovitch cycles) is actually irrelevant, since those operate on timescales of rough multiples of 22,000 years. That comparison would be like worrying about whether a variation in the weather could be having an effect on the slow-down of a spinning top: the timescales are so different that there isn’t a useful physical connection between the phenomena.

The person visits his doctor complaining about tiredness. Tests point out that the person is generally healthy, but he is overweight. The doctor recommends a diet and exercise. The doctor warns about potential catastrophic consequences if the person doesn’t lose weight.

The person is skeptical. He thinks that cutting back on food is the wrong thing to do if you feel like having a lack of energy. Spending money to exercise in a gym and feeling tired afterwards is a stupid thing to do if you could have spend the money to buy a few Big Macs. After eating the Big Macs you have the energy to continue to play video games until bedtime.

The starting point for the claim that extra CO2 causes global warming is the calculation that every doubling of atmospheric CO2 concentration should result in a 3.7 W/m^2 average radiative imbalance, as calculated by normal techniques in radiative transfer theory. This is the motivation for the concern for warming; it is not based on correlation with temperature as such.

Furthermore, explanations alternative to CO2 and other human causes run afoul of the time-frame issue: the proposed non-human causes do not synchronize with the putative effect. In particular, over the last 20 years solar luminosity has not varied by more than one part in 1000. Likewise, variation in cosmic-ray intensity has been cyclical, not secular.

So in the case of CO2, you have an explanation that matches the results (in combination with other known factors, like sulfate emissions and volcanic eruptions) in timing and magnitude; or alternatively, you have proposals that don’t have the right time behavior to explain the results, with uncalculated magnitude.

So, on the one hand, a plausible explanation based on CO2 from fossil fuels; on the other hand, a handful of proposals, none of which really satisfy the basic requirements of an explanation. How to decide?