I’ve read and enjoyed both your books. But I am firmly in the camp that AGW is a serious problem that demands some public policy prescriptions. I’ve read many of the leading skeptics, and I appreciate your (and Dr Lindzen’s) work primarily for two reasons — (1) you acknowledge things that simply have to be acknowledged as observational fact (i.e. the CO2 measurements are rock solid), which I think enhances your credibility, and (2) you try to contribute to the scientific discussion (unlike many on the skeptic side who just shout “conspiracy” and “cooked data,” and many on the AGW theory proponent side who just demonize industry and scream “denier”).

What I’d really like to know from you is (a) what would it take to convince you that human CO2 emissions are now in control of the climate and are something to worry about, and (b) how long do we wait for your PDO (or Lindzen’s cloud) theory to change the trends. On the second point, the PDO obviously went negative in 2008, yet even by your satellite records 2009 and 2010 were and are anomolously warm. I understand your kettle on the teapot analogy (from your book), but how long before we can expect the PDO to cause cooling from its negative cycle? Relatedly, how come the clouds of Lindzen’s iris theory haven’t protected us from warming so far and how many years of warming will it take for that theory to be dropped (assuming it continues to warm at current rates).

I know this sounds contrarian, and I don’t mean to be confrontational … it’s you site after all and you do not need to answer folks like me. But I teach the science of climate change during the first couple weeks of my law school class each year, and I do my best to present a balanced view. You and Lindzen are two whose views the students should be made aware of as they make their own determinations on the credibility of the science.

One last question (sorry). Is there any empirical evidence to support either your view or Lindzen’s (i.e., can we compare current cloud cover to the past, or do we still not have the observational tools and methods to do that (I understand we can measure the atmospheric water vapor content, but I’m asking specifically about clouds)). Also, does your theory necessarily conflict with Lindzen’s? He says warming will cause more low level cloud cover, which will reflect incoming solar radiation. You say cloud cover resulting from the warm PDO may actually be the cause of the current warming trend. Is there a way to harmonize these two major premises?

Many thanks.

You are right in that it if there is an annual signal in the data, it will show it, but it will be smoothed with the rest of the year so it won’t show up as a huge effect.

A 13 month average just presents a tidier picture. A lot easier to see the ‘natural variation’ cycles at work.

Monthly plots merely show weather.

Dr Spencer tried a 25 month average but the ‘record breaking we are all going to fry’ year of 1998 lots it’s spike and various folks complained.

Personally, I liked the 25 month average. It showed a ‘gradual’ warming trend in a sea of natural variation, I.E. Climate rather then weather.

The graph is using anomaly data, rather than absolute temperatures. So the globe being warmer at certain times of year will not matter, what matters is if the globe is warmer than usual for that time of year.

I’m not sure if there’s a seasonal signal in the anomaly data or not.

- How is the Earth Average Temperature calculated?

Naively, I imagine it is for each station a (Tmin+Tmax)/2, then a “gridification” (so average of several stations if they are close, or interpolation if stations are missing) and then an average of the gridded data (no surface-weighted as grids are designed of equal surface, probably). For sattelites, it is probably an integrated average (not gridded).

Now however Temperature is not an extensive physical property. I cannot compute the average temperature of two reactors whose content I intend to mix without correcting for the heat capacity, for instance, and weighting by the quantity (e.g. mass). In order for the procedure
given above to be physically correct, we must consider that masses per volume unit and heat capacities are the same globally.

But for instance, the heat capacity of air is dependant on the humidity. 2% of humidity (saturation at 25°C) increases Cp of air of 1.7%. This gets order of magnitude worse if the air is over-saturated (clouds/fog/rain) or close to saturation as evaporation enthalpies can play a role and dominate massively (about factor 1000). If I imagine a process by which the atmosphere over the tropical ocean (assumed saturated) cool but the atmosphere over land and polar oceans (deemed dry) warm, I could have a spurious warming signal while the energy remain constant.

Worse: pressures on Earth vary from extremes of 109.4kPa to 87kPa. This is extreme and “normal” range is 97-104 mbar. This is a difference of 7%. As in a (perfect) gas the pressure and the temperature are inversely proportional we may naively assume a difference in temperature of 7% or (based on Kelvin of course) 20°C!
To illustrate let’s imagine that half Earth is high pressure 104mbar and the other half is low pressure 97 mbar. IF I had a process that tendancially would warm in a decade the low pressure zone (+1°C) and cool the high pressure zones (-0.93°C), the simple average would show
a warming trend (+0.035°C/decade) while actually the Energy in my system remained CONSTANT!

Remember the signal we have is +0.8C since a century. This is in Kelvin (we want energy content) a deviation of 0.3%, or one full order of magnitude lower than the difference in ernergy due to pressure variations alone… and it is important, because the causes of real signal vs. spurious signal due to energy relocation might be quite different…

Do you know if the average air temperature is calculated accordingly?

If yes, do they complement it with measures of pressure (easy) and humidity (hard)? While this is technically feasible since 1979 and satellites, how was it done historically (I double hygrometry was manually measured at each whether station, see http://en.wikipedia.org/wiki/Hygrometer#Difficulty_of_accurate_humidity_measurement)?

All-in-all, the correct metric for global warming would be “total energy of the Earth”. Perhaps beacuse it is slow to reach equilibrium, it makes sense to limit ourselves to the total energy of the atmosphere + a very thin layer of ocean/earth. But it is certainly highly debatable to take trends in atmospheric temperature in a system that is obviously not at equilibrium.