Executive Summary

To me, it is refreshing to see markups in the IPCC 4th Assessment Summary for Policy Makers . It's out even if there are still places where the units are still being converted or the wording is shifting. They know what they mean and mean what they say but consensus takes work all along the way.

Real Energy is what the report is all about, or at least an abstraction of real energy. The units are given in equivalent solar forcing, watts per square meter all over the place. So, green house gasses add some of these and aerosols subtract some of these, and the change in the reflectivity of the Earth takes away some. The equation comes to people do 2.3 (greenhouse gasses) -0.5 (aerosols) -0.5 (cloud formation because of our aerosols) +0.35 (because we also make smog) +0.34 (evaporation of fuel) -0.2 (changing the reflectivity through land use) and +0.1 (making the snow dirty) which comes to 1.9 W/m^2. From the Sun we get an estimated extra 0.12 W/m^2 since 1750. What is really important about these numbers is that the uncertainties have been estimated. You can't be confident of what the consequences of these measurements are until you know how well the measurements have been done. For the last number the range the report gives is 0.06 to 0.30 W/m^2 and the solar constant is about 1400 W/m^2 so we now work to about 0.004%. As an astronomer, that makes be feel pretty proud. In ground based mid-infrared astronomy we start at about a part in a million just to measure anything at all, but measuring the Sun is actually a more difficult problem.

Now, all of these numbers are changes from 1750 AD and all but the one for the Sun are changes that happened because of what we've been doing. And, what we've been doing has been happening most in the last 4 decades so we really ought to take this into account if we want to look at the relative importance of what we do and what the Sun does. In a rough way we can just multiply what the Sun does by the ratio of 4 decades to 25 decades or about 0.15 which means that what we're doing is about 100 times more important than what the Sun is doing in terms of changing the temperature of the Earth. Isn't it great to know something with quantified uncertainties?

All of this is about physical measurement and modeling but there is more to the report. The report also looks at how the climate is likely to behave based on different ways that we might behave in the future. Here, estimates of political, economic and demographic conditions in the future are assumed and the amount of greenhouse gas emissions are projected from that. The demographic numbers are probably the soundest portion of these though they all feed into each other. China, for example, is retaining its one child policy which is a political impact on demographics. Now all of this is very uncertain because the future of human behavior is notoriously unpredictable. There are always a few seers who get it mostly right, but knowing which ones those are is very hard to do.

What I find really important about the assumptions about future human behavior is that they do not include any reasonable ones. The report ignores completely the effect of meeting Kyoto and going forward from there. This is a huge hole in the report because it hides the estimated results of policy initiatives that are already underway from policy makers.

While it is true that until about the end of 2006, the prospects of meeting Kyoto obligations looked bleak for a number of countries, some have made real progress which means that there are models that work. The prospect of a major effort by the rest of us to meet the end of the 2012 compliance period is not really impossible, but it's been excluded from consideration.

At the end of 2006, sales began for long term rental contracts for solar power that cost no more than what utilities charge for delivered electricity. This is possible because the cost per peak Watt is now $1.53 owing to large scale production. Because the contracts are fixed rate, they actually cost less than taking delivery of power from a utility in the inflation regulated economic environment we've maintained since the seventies.

For the US to meet the Kyoto obligations it needs to reduce it's emissions by about 20% from current levels. We get a pretty good shot at that if we build about forty 500 MW per year capacity solar panel fabrication plants by 2011. That's one plant per net metering state, a tall order, but not beyond what could be done given that there is an economic incentive to do so. Taken together with increase in wind capacity and the introduction of plugin hybrids which make a lot of sense in the current high oil price environment, meeting the Kyoto obligations is not out of the question for either the US or Australia regardless of good faith issues affecting both countries.

So, as an advance on quantitative understanding of global warming, the report is really really nice, but in terms of modeling the effects of pursuing various policy options, it is pretty much a failure since it excludes the economically most likely scenarios.