To warm or not to warm

Is the science of global warming really settled?

I recently listened to an interesting podcast from the CBC (the Deniers), interviewing a skeptic of global warming. Many other deniers are out there, so it is a pressing question. Its importance is huge.. none could be greater, so I will try to get to some data. Of course, a true firehose of debunking comes from the blog climateprogress, so go there if you want chapter and verse.

What I am reading in the scientific literature clearly indicates that global warming is happening, will get substantially worse, and needs to be mitigated to avert rapid global change. Unfortunately, the catastrophe is more relevant for our silent co-passengers on planet earth than it is for humanity. And it will be far more serious for our poorer human co-passengers than for inhabitants of rich countries who are making all the mess. If global warming is true and imminent, the most important case for its mitigation is moral and aesthetic- the duty we have to our fellow creatures and to the biosphere generally to keep it healthy and beautiful instead of turning it into a science fiction dystopia. Warming is just one more facet of harm we are doing to the biosphere, in addition to fishing out the oceans, filling them with trash, driving species to extinction, and destroying ecosystems by a thousand cuts.

The CBC interview was with Lawrence Solomon, head of Energy Probe Research Foundation, a Canadian environmental organization. This is a right-wing think tank with apparently serious environmental credentials (only in Canada!), one of whose aims is to solve common goods problems by extending private ownership over common goods. How that would work with the atmosphere.. well, their web site is unhelpful on that score.

In the interview, Solomon brings up several substantive points:

1. The famous "hockey stick" curve was based on bad science and bad statistics, and has since been withdrawn, even by its sponsor, the Intergovernmental panel on Climate Change (IPCC).

2. Prominent scientists are lining up on the denier side, such as Freeman Dyson. Typically, scientists at the end of their careers are the only ones free enough to take this position, since it can be deadly to anyone still building a career, in view of the heavy bias in the scientific community on the other side.

3. The current decade has been cooler than the last one, and the last one was not the warmest ever, as advertised, but only the second warmest, second to the 1930's.

4. Climate models are not well-made and the climate is not as well undestood as some would have us believe. How do clouds affect the system? How is their origin related to CO2? How much do aerosols cool the earth? How, if regular weather forcasts are poor just 7 days in advance, are we to take seriously climate models that purport to forcast decades ahead?

5. Isn't CO2 the gas of life? OK- this is not a serious point, but he does raise it towards the end, as both participants seem to let down the guard of the interview as a serious, scholarly dialog.

I'll take these points in reverse order.

5. Solomon said nothing about the general theory that CO2 is a greenhouse gas, and thus by any reasonable model, that more CO2 leads to higher heat retention from solar radiation. The example of Venus is instructive and frightening. The real question is whether the amounts of CO2 in question (the recent rise from pre-industrial levels of ~280 parts per million [ppm] to the current 380 ppm and rising) are significant- how much warming they (and future increases) might cause. This was not discussed. To say that they cause no warming is not plausible. To say that they cause so little as to be noise in the system might be conceivable, but my impression is that the data disagree strongly.

The history of the earth is quite interesting in this respect. We started out much like Venus, with large amounts of CO2, but with our larger distance from the sun (getting roughly half the light per unit area), we were not trapped in a greenhouse from the start. Additionally, the sun was less luminous at earlier times and earth was blessed with huge amounts of water. Over time, earth's CO2 was mostly withdrawn from the atmosphere by mineral deposition (limestones, etc.), and by life, which in turn created all the atmosphere's oxygen (which was strictly absent from the early atmosphere). An interesting illustration in a recent Science magazine graphs out what we know of the relative CO2 levels over the last half-billion years:

The "RCO2" on the Y-axis is relative CO2, relative to the present level of ~350 ppm at one. The end of the high-CO2 era (400 to 300 MYA) corresponds to the Carboniferous period of geologic history, which is to say, the time when huge amounts of carbon were withdrawn from the atmosphere and deposited in coal beds and other geologic formations by living organisms. Oxygen levels were also high, allowing some insects to grow to enormous proportions, like desk-size dragonflies with 75cm wingspans. The whole earth was a big sauna, apparently, though the era ended with glaciations, as one can infer from the plummeting CO2.

For the last 800,000 years, the CO2 content of the atmosphere has varied cyclically between ~180 and ~280 ppm. (Indeed the paper I am taking this from extends this observation to "These results show that changes in pCO2 and climate have been coupled during major glacial transitions of the past 20 myr, just as they have been over the last 0.8 myr, supporting the hypothesis that greenhouse gas forcing was an important modulator of climate over this interval via direct and indirect effects." So we are going in an unprecedented direction, which alone is cause for trepidation and action.

4. Climate models are indeed rather complex affairs, and not all variables are equally easy to model. For instance, geenhouse forcing is easy to model- the infrared heat emitted from the earth after absorbing sunlight is trapped by CO2, water vapor, methane, and the other greenhouse gasses. On the other hand, the formation of clouds seems to be less easy to model, depending more on the dynamics of the winds and interactions between layers of different temperature. So there is quite a bit that is not known, and the specter of chaos theory and complexity hangs over some of these issues. Yet on the other hand, physics-based climate models have gotten very good, being able to model past events as a test for forward predictions. And of course the news lately has been that warming in the arctic has been faster than virtually all models predict, so they may be excessively conservative (possibly due to positive feedback effects that accelerate climate change and may not be modeled yet).

3. The current decade is the hottest on record, as shown by the following graphs taken from a recent Science article (and see these graphs for up-to-the-minute data). The interesting thing is that the current decade should instead have been cooler, based on slight declines in solar flux (due to a quiet phase in the sunspot cycle, among other issues). So this persistent rise in temperature is all the more significant.

Indeed, one other interesting aspect of this graph is that it tracks a long-term cooling trend for the rest of the last 2000 years (gray line, which focuses on temperatures in the arctic). The top-most line (F) tracks a slight long-term decline in solar input to the northern hemisphere due to solstice precession, which provides a rationale for this long-term cooling trend. So we might possibly have been headed for a new ice age. We may be thankful to our emissions staving off that catastrophe, but it is obvious that we are over-shooting in the other direction.

2. A few scientists have been casting suspicion on global warming. Well, a few scientists cast suspicion on HIV as the source of AIDS as well. There are good reasons why the scientific consensus has coalesced around global warming for well over a decade, some of which are given above. The combination of solid data and solid theory makes for a compelling case. The fact that the data had not, up until the last few decades, risen above the climate noise in a way apparent to the most jaded and critical observer is unfortunate, but no reason to criticize those who were right rather than those who have been wrong.

A countervailing view of eminent scientists is that they often wade into areas about which they know very little (Freeman Dyson), and they may hunger for a larger spotlight, which they can only gain by bucking a consensus (Richard Dawkins), whether sensibly or not. The history of Nobel Laureates is littered by such crankiness (Nobelesse oblige?). Criticism of this kind serves a critical function, of course- to hold a consensus's feet to the fire, as it were.

As a biologist, some of the most convincing evidence for me (aside from sea level rise and many other indicators) has been the relentless migration of plant and animal ranges northward. This process is just the kind of long-term, slow change that evens out noise from the system and reflects underlying changes of climate. Montane species, like pikas in the Sierras, can not just pick up and head north into the Yukon- they may run out of habitat entirely.

1. Lastly, the hockey stick graph. As shown above, despite all the controversy about earlier versions and their somewhat exagerated data, the basic graph is correct. It may have been a little ahead of its time, as was true for Gregor Mendel as well, as some scientists compromise the integrity of their process (data collection and presentation) while tripping over themselves to show a result they have become convinced of, and which may be vindicated by later, more careful work. Such shoddiness can not be excused, but climate change is one more classic case where the truth was due to come out sooner or later, and is now on completely firm ground.

In this case, the better jump we have on the phenomenon, the more rational and moderate our policy response can be. So spending the last decade on disinformation from the fossil fuel industries, the Lomborg acolytes, and George Bush's imitation of an ostrich, has been extremely damaging for our long-term ability to mitigate the climate change that is already happening, much more of which is set in concrete for decades to come. Since the climate is the ultimate commons, it is particularly difficult to address from a game theory/economic perspective, making this loss of time doubly damaging.

• NYT covers the IPCC blues
• Arctic warming, NYT.
• Northwest passage- opened for the first time in 2007, then also in 2008
• No impact guy on what we would gain, even if the science was all wrong
• Ooops- I missed blog action day!
• A nice philosophically couched discussion of global warming and scientific uncertainty.
• A sample skeptic blog
• A delightful essay on science, over at the Oracle blog
• On the evolution of the ear, with intermediate forms!
• Religion on Wall Street
• A fine page on Schopenhauer
• Gregor on the vise of recession + rising oil prices
• OK, let's just clear the air on this whole religion thing!