Yeah, Venus was a bad analogy and Joanne took that and run.
Here is a more impartial response from two Atmosphere Science Professors/Researchers (
chron link):
1. "The greenhouse signature is missing."
Here the handbook is referring to the expectation that temperatures in the tropical upper troposphere should warm faster than temperatures in the tropical lower troposphere. Supposedly its absence is evidence that something else other than greenhouse gases caused the warming in the lower troposphere.
You fall into the trap here if you accept the premise that enhanced warming in the tropical upper troposphere is a "greenhouse signature". It's not. A signature is something that is unique to a particular entity, in this case greenhouse gases. But enhanced warming in the tropical upper troposphere is expected from any warming of the tropical ocean, from whatever cause. It's a simple consequence of convective adjustment in the tropical atmosphere.
This is a legitimate debating point for those who wish to discuss the interaction of tropical clouds and radiation, or the relative accuracy of surface vs. upper tropospheric temperature measurements. But it has nothing to do with what causes changes in global temperatures.
2. "The strongest evidence was the ice cores, but newer, more detailed, data turned the theory inside out." Here the handbook is referring to the relationship between temperature and CO2 levels during glacials and interglacials. Supposedly something else caused the warming.
You fall into the trap here if you accept the premise that ice cores are prima facie evidence that CO2 causes global warming. And hey, you'd be in good company if you fall into this trap, since Al Gore fell into this trap and encouraged his audience of millions to fall into this trap too.
No scientists that I know of, and not even Al Gore, looked at the temperatures and CO2 from the ice cores and concluded that low CO2 caused the ice ages and high CO2 caused the interglacials.
The prevailing theory was, and still is, that Milankovitch cycles (orbital variations) trigger ice ages and interglacials. But the changes in snow cover and glaciation, and the resulting changes in albedo, were not large enough to account for the temperature changes, and the feedback from CO2 and methane, as documented in the ice cores, provided the missing source of energy variations.
What does overlaying temperature and CO2 from ice cores prove? It proves that during glacial periods, the oceans were colder and absorbed more CO2 from the atmosphere. That's it. You've got to calculate the radiative impact of those CO2 changes to figure out whether rising CO2 levels in turn caused temperature to rise even farther. It turns out it did, but just as orbital variations weren't responsible for the full magnitude of temperature swings from glacials to interglacials, neither was CO2. Now if only Al Gore had openly said what the scientists have known all along.
The handbook has an answer for the statement that CO2 was an amplifier. It says that if CO2 was a major driver, temperatures would rise indefinitely in a runaway greenhouse effect. Huh? Apparently CO2 can't cause global temperatures to rise 3 C because, well, it just can't. It either has to be a lot more than 3 C, or a lot less. Why? Just because.
3. "Temperatures are not rising." The handbook goes on to ask, "How many more years of NO global warming will it take?" I essentially answered this question two blog posts ago, saying that it depends on what causes the temperatures to remain flat...volcanoes, solar activity, etc. The handbook goes on to say "While temperatures have been flat, CO2 has been rising, BUT something else has changed the trend. The computer models don't know what it is."
Side issue: it doesn't matter that CO2 has been rising over the past 8 years. The impact on the climate of that additional CO2 over the past 8 years is trivial compared to what's been emitted before. Computer models predict that temperatures would be climbing even if CO2 concentrations were flat for the past 8 years. And I can guarantee you that if CO2 concentrations actually had been flat, and temperatures were climbing, we'd see people citing THAT as evidence against anthropogenic global warming too.
Back to the main issue, which is a red herring. Computer models don't know anything, they're computers. But meteorologists know that things like
El Nino, the Pacific Decadal Oscillation, etc. have significant temporary effects on global temperatures, as does the 11-year (or so) sunspot cycle. Does anybody actually think that increasing CO2 will cause El Nino, the PDO, and the sunspot cycle to go away? Well, El Nino frequency and intensity might change, but meanwhile there will always be decade-long ups and downs along the way to a warmer climate, and they don't prove anything other than
CO2 is not the main driver of climate change from one year to the next. Its effects are slower, and longer-term.
4. "Carbon dioxide is already doing almost all the warming it can do." Here the handbook is referring to the fact that the impact of CO2 is logarithmic. The handbook says that means that CO2 is a "bit-part player", but doesn't really say why.
Let's consider the greenhouse gases. The most plentiful one, by a factor of 50, is water vapor. It's filled up large swaths of the infrared spectrum with total absorption. Yet its variations are still important radiatively, in fact they're more important directly than all other greenhouse gases combined. You can't predict day-to-day temperatures accurately without taking into account the radiative effects of water vapor variations. (P.S. water vapor is not cloud.)
The next most plentiful one is CO2. Because CO2 has filled a few segments of the infrared spectrum, its radiative impact is logarithmic, as the handbook says. That's why, when considering the impact of CO2, we always talk about CO2 doubling. (Recall your high school math, or ask a nearby high school student.) That's why an increase of 280 ppb of CO2 is expected, along with the fast feedbacks, to produce "only" a roughly 3 C rise in global temperatures, when the first 280 ppb was responsible for much, much more.
Other greenhouse gases, in turn, are much less plentiful than CO2. And because they are less plentiful, each molecule individually has a bigger impact on the greenhouse effect than each individual CO2 molecule, by a factor of 10, a factor of 100, or even more. But since they are at such low concentrations, their net combined effect, all added together, doesn't equal the effect of the rising CO2 levels. So the logarithmic dependence of greenhouse effect on CO2 concentrations also turns out to be a red herring.
Beware the skeptic brandishing the Skeptic's Handbook. Hopefully, after reading this blog entry, you'll be able to cut through the red-herrings and avoid the traps.
