It is a bit tricky to respond to Manzi’s comments on my essay, because he chose to selectively ignore the evidence I presented and thus never rebutted my central points. So I will elaborate here on the discussion he ignored, since it goes to the heart of why he is wrong, why Goklany is wrong, and why Shellenberger and Nordhaus are wrong.
Manzi’s central point on warming is that “The current IPCC consensus forecast is that, under fairly reasonable assumptions for world population and economic growth, global temperatures will rise by about 3°C by the year 2100.”
That is simply an incorrect statement, as I explained in my original post. Manzi is under the serious misimpression that the IPCC scenarios like B1 or A1F1 either separately or averaged together, represent a consensus or business-as-usual forecast, when in fact most of those scenarios assume the kind of aggressive action to deploy clean energy technologies that he does not support. Moreover, since 2000, the growth rate of actual global carbon emissions have exceeded even IPCC’s most extreme A1F1 scenario — so again it makes little sense to average all of IPCC’s scenarios to get business as usual or even a “fairly reasonable assumptions for world population and economic growth.”
Manzi might try reading Pielke et al.’s “Dangerous Assumptions,” in Nature — an analysis that I don’t entirely agree with — to understand where he went wrong. Manzi then writes:
Mr. Romm says that my statement is “not correct,” and then goes on to provide what he believes to be a more accurate representation of IPCC projections for expected levels of warming by 2100:
“…the latest IPCC report finds that, absent a sharp reversal of BAU trends, we are headed toward atmospheric levels of carbon dioxide far exceeding 1,000 parts per million by 2100. IPCC’s “best estimate” for temperature increase is 5.5°C (10°F)…”
Note that this asserted projection is much more severe than what I presented (5.5°C vs. 3°C), and unlike my assertion is based on a BAU trend. He supports this assertion with a general link to this same WG1 SPM document that I have referenced and discussed. I am pretty familiar with this document… .
No, I do not support this assertion with a general link to this same WG1 SPM document. It is a bit unusual for Manzi to try this kind of selective editing in an online debate where everybody can see what he did. Let me reprint what I actually wrote
As I explained in a recent Nature online article, the latest IPCC report finds that, absent a sharp reversal of BAU trends, we are headed toward atmospheric levels of carbon dioxide far exceeding 1,000 parts per million by 2100. IPCC’s “best estimate” for temperature increase is 5.5°C (10°F), which means that over much of the inland United States, temperatures would be about 15°F higher.
It is my recent Nature online article that offers the explanation. Nature online asked me to write it in reply to the Pielke et al. piece and it explains the remarkable implications of the latest IPCC reports that most people, including Manzi, missed.
Buried on page 16 of the Working Group 1 Summary for Policymakers is perhaps the most alarming yet under-reported paragraph in the entire document, which I summarize in the Nature article.
According to the IPCC’s Fourth Assessment Report in 2007, model studies based on our current understanding of climate-carbon-cycle feedbacks suggest that to stabilize carbon dioxide levels at 450 ppm could require that cumulative emissions over the twenty-first century reach only about 490 gigatonnes of carbon (GtC), which equates to less than 5 GtC per year.
Similarly, stabilizing atmospheric carbon dioxide levels at 1,000 ppm would require cumulative emissions this century of only about 1,100 GtC. In other words, if annual emissions average 11 GtC this century, we risk the real, terrifying prospect of seeing 1,000 ppm carbon dioxide in the atmosphere and and a ‘best estimate’ warming of a staggering 5.5 °C by the end of the century.
Carbon emissions from the global consumption of fossil fuels are currently above 8 GtC per year and rising faster than the most pessimistic economic model considered by the IPCC. Yet even if the high price of energy from fossil fuels and power plants combines with regional climate initiatives to slow the current rate of growth somewhat, we will probably hit 11 gigatonnes of carbon emissions per year by 2020.
The first question to ask is — what is the IPCC’s ‘best estimate’ warming for 1,000 ppm of CO2? Here I used the wrong link in my essay. This does not come from the WG1 Summary for Policymakers. The right link is the WG1 Technical Summary. On page 66 of the Technical Summary, a table lists the “best estimate” warming for different atmospheric levels of carbon dioxide equivalent, which is obviously going to be higher than the atmospheric level of carbon dioxide alone. In any reasonable business-as-usual case where there is no greenhouse gas constraint, then you would expect steady rises in the levels of other greenhouse gas emissions.
The best estimate warming for 1,000 ppm of CO2eq is 5.5°C and the best estimate for 1,200 ppm of CO2eq is 6.3°C. Given how much effort will be required to merely stabilize atmospheric concentrations of CO2 alone at 1,000 ppm (discussed below), I think it is very safe to say that total business-as-usual warming is at least 6.3°C and that 5.5°C is conservative.
How fast could this happen? Again, climate scientists don’t spend a lot of time studying this nightmare scenario because they can’t imagine humanity would be so stupid as to let it happen. But as I cited in my original essay, one very credible model suggests we could hit 1,000 ppm of CO2 in 2100 with a total warming from preindustrial levels in 2100 of about 5.5°C.
Further, to my knowledge there is no marker scenario presented in this document or anywhere in the current IPCC Assessment Report under which the best estimate for warming by 2100 is 5.5°C. I do not understand the basis for Mr. Romm’s assertions.
Well, there may not be a “marker scenario” but anyone who reads the full IPCC report can clearly see that the report raises the very serious prospect we may hit 1,000 ppm of CO2 and asserts that would probably warm the planet 5.5°C.
The second question to ask is: What would be required merely to keep global emissions frozen at 11 GtC through most of the rest of the century starting in 2020? As I explain in the Nature piece:
I use the “stabilization wedges” approach put forward by Robert Socolow and Stephen Pacala of Princeton University to answer that question qualitatively. As Socolow and Pacala explain “A wedge represents an activity that reduces emissions to the atmosphere that starts at zero today and increases linearly until it accounts for 1 GtC/year of reduced carbon emissions in 50 years.” So the planet would need 11 wedges to keep emissions flat at 11 GtC per year from 2020 to 2070.
I then offer one possible list of 11 wedges:
- Concentrated solar thermal electric: 1,600 gigawatts peak power
- Nuclear: 700 new gigawatt-sized plants (plus 300 replacement plants)
- Coal: 800 gigawatt-sized plants with all the carbon captured and permanently sequestered
- Solar photovoltaics: 3,000 gigawatts peak power
- Efficient buildings: savings totaling 5 million gigawatt-hours
- Efficient industry: savings totaling 5 million gigawatt-hours, including co-generation and heat recovery
- Wind power: 1 million large wind turbines (2 megawatts peak power).
- Vehicle efficiency: all cars 60 miles per U.S. gallon
- Wind for vehicles: 2,000 gigawatts wind, with most cars plug-in hybrid-electric vehicles or pure electric vehicles
- Cellulosic biofuels: using up to one-sixth of the world’s cropland
- Forestry: end all tropical deforestation
Each of these wedges represents a staggering amount of effort by both the public and private sectors. For instance, one wedge of coal with carbon capture and storage represents a flow of carbon dioxide into the ground equal to the current flow of oil out of the ground. It would require, by itself, recreating the equivalent of the planet’s entire oil delivery infrastructure over the course of five decades.
Obviously this is not business as usual. Indeed, it is very safe to say this won’t occur without a very aggressive collective effort by the nations of the world, an effort that the Manzis and Goklanys of the world do not support. But here is the really scary part:
Achieving all 11 wedges would still keep us on a path towards atmospheric levels of 1,000 ppm of CO2eq by 2100, some 5.5°C total warming from preindustrial levels and a variety of catastrophic impacts, including the extinction of most species, the desertification of one-third of the planet, and a return to temperatures not seen since the Earth was ice-free and sea levels were 250 feet higher (points I will return to in Part 2).
What must America and the rest of the world do to avert this catastrophe? Obviously we must do much more then deploy 11 wedges from 2020 to 2070. As I noted in Nature:
If we are to have confidence in our ability to stabilize carbon dioxide levels below 450 ppm emissions must average less than 5 GtC per year over the century. This means accelerating the deployment of the 11 wedges so they begin to take effect in 2015 and are completely operational in much less time than originally modeled by Socolow and Pacala, say in 25 years. As a result, in 2040 global emissions would be at about 4 GtC per year. We would then have six decades to cut emissions in half again (or by more if the science deems it necessary), which would require an equally impressive effort.
Needless to say, that requires government action of a scale that Manzi and Goklany oppose, and that the wishful thinking of Shellenberger and Nordhaus is exceedingly unlikely to achieve.