Hopefully people interested in the blog wars have been alerted to the ongoing climate change “debate” between George Monbiot and Ian Plimer. If not, the best place to start is probably Monbiot’s blog itself (with several posts on the topic already). Greenfrye and Tamino also have some ongoing commentary, so have fun catching up on what’s going on.
Unfortunately, round 1 consisted of Plimer dodging Monbiot’s questions which ask Plimer to defend certain indefensible statements in his book “Heaven and Earth.” Maybe Plimer just “wanted to go first” so I’ll give him the benefit of the doubt, but his own set of questions intended for Monbiot are quite revealing about his intentions.
As most commenters have suspected, these questions are all ill-posed or have nothing to do with the attribution or prediction of future climate change. In most cases, if an answer is even possible, it’s not very meaningful information. It’s just a distraction, something Monbiot wanted to avoid in his debate conditions. They’re an obvious way to let Plimer set the tone of the “debate” by making it sound scientific to readers who know nothing about the subject. I’m not going to “answer them” in much detail but just to address the tactics behind a handful of them I am creating a post. I will open up commenters to address some other ones.
1. From the distribution of the vines, olives, citrus and grain crops in Europe, UK and Greenland, calculate the temperature in the Roman and Medieval Warmings and the required atmospheric CO2 content at sea level to drive such warmings. What are the errors in your calculation? Reconcile your calculations with at least five atmospheric CO2 proxies. Show all calculations and justify all assumptions.
It is rather strange why Plimer requests agriculture as a proxy for paleotemperature (and what’s stranger is what this has to do with anything). The answer about the error is simply that it will be “large” and will not be indicative of global temperatures, even if temperature is the dominant climatic variable picked up by changes in vines and crops. What’s more interesting is the statements about Carbon Dioxide. Plimer plays an interesting trick here and assumes that these climate changes were in fact caused by Carbon Dioxide (which they weren’t). The question about CO2 content at sea level is a hypothetical question (how much CO2 would it take to cause the climate change?), but then he asks Monbiot to reconcile this with observations (I’m not sure why he needs five, I’d just use ice core records here as a starting choice.) But what if CO2 didn’t cause those warmings? In that case, Monbiot could answer the hypothetical first question, but there would be nothing to answer for the second part of the question since the justification itself would be expected to be void. It’s like if someone asked me how much the globe would cool if we removed all the CO2 from the atmosphere (which is an interesting question) but then asking me to back that up with proxy data, as if this actually happened before. Even to answer the first question about “CO2 content” would include some caveats since it’s the *change* in CO2 that matters for driving warming, not the absolute content, and it’s the fractional increase (not the absolute increase) that matters and so you’d need to know the baseline value of CO2. This is not difficult to get from proxies (and not much different from pre-industrial values) but the question as stated makes little sense. Furthermore, CO2 is well-mixed in the atmosphere and so there’s no reason to confine the question to sea-level, especially since CO2 in the upper atmosphere matters significantly for radiative transfer.
Tabulate the CO2 exhalation rates over the last 15,000 years from (i) terrestrial and submarine volcanism (including maars, gas vents, geysers and springs) and calc-silicate mineral formation, and (ii) CH4 oxidation to CO2 derived from CH4 exhalation by terrestrial and submarine volcanism, natural hydrocarbon leakage from sediments and sedimentary rocks, methane hydrates, soils, microbiological decay of plant material, arthropods, ruminants and terrestrial methanogenic bacteria to a depth of 4 km. From these data, what is the C12, C13 and C14 content of atmospheric CO2 each thousand years over the last 15,000 years and what are the resultant atmospheric CO2 residence times? All assumptions need to be documented and justified.
The whole point here is to sound smart. There’s nothing here remotely relevant to what Monbiot wanted to debate. One can certainly pull up tree ring or ice core data to get C13/C12 ratios as a time-series, or (probably more relevant) CO2 concentration in the atmosphere whose fluctuations will tell you something useful about net emission/uptake and whether the carbon cycle has been perturbed, as well as residency time. We don’t know emissions from every individual source and there’s also not much point in throwing the “From these data…” connection since certain proxies record CO2 content in the atmosphere to pretty high accuracy without knowing where it came from.
From first principles, calculate the effects on atmospheric temperature at sea level by changes in cloudiness of 0.5%, 1% and 2% at 0%, 20%, 40%, 60% and 80% humidity. What changes in cloudiness would have been necessary to drive the Roman Warming, Dark Ages, Medieval Warming and Little Ice Age? Show all calculations and justify all assumptions.
Changes in cloudiness at 0% humidity indeed!!
Obviously some of these situations are unphysical and so preclude any realistic calculation and cloud change is generally thought to be a feedback. It also depends not only on cloud amount but distribution of cloud type, as changing high clouds and low clouds (or for example one could decrease the area coverage but increase the cloud top altitude) would have different, even competing effects.
One crude estimate presented by Dennis Hartmann is his book “Global Physical Climatology” is that the fractional area of cloud cover is about 50% and has a net -20 W/m2 impact on the energy balance, and thus the partial derivative of the net radiative energy input at the TOA with respect to the total fractional area of clouds would imply that a 10% change in cloud fraction would either offset or double the RF for a doubling of carbon dioxide.
From ocean current velocity, palaeotemperature and atmosphere measurements of ice cores and stable and radiogenic isotopes of seawater, atmospheric CO2 and fluid inclusions in ice and using atmospheric CO2 residence times of 4, 12, 50 and 400 years, numerically demonstrate that the modern increase in atmospheric CO2 could not derive from the Medieval Warming.
Bascially in an overcomplicated way, Plimer is asking to show that the modern rise in CO2 is not a feedback from medieval warming. This is probably some offshoot of the whole “CO2 lags temperature” line. One issue here is that the perturbation lifetime of CO2 is different than the “lag time” which occurs as a response to warming. Even then no one expects an abrupt decadal scale rise of CO2 centuries after the event, which isn’t even what occurred in the glacial-interglacial cycles, which were considerably larger in magnitude and spatial extent then the MWP. The rate of change is today of CO2 is orders of magnitude larger, and the absolute concentration is also much higher than the whole ice core record show and even much longer. We also know that today’s CO2 increase is anthropogenic because CO2 is going into the ocean (ocean acidification, duh) not going out and isotopic signatures of light and heavy carbon changes.
From the annual average burning of hydrocarbons, lignite, bituminous coal and natural and coal gas, smelting, production of cement, cropping, irrigation and deforestation, use the 25µm, 7µm and 2.5µm wavelengths to calculate the effect that gaseous, liquid and solid H2O have on atmospheric temperature at sea level and at 5 km altitude at latitudes of 20º, 40º, 60º and 80ºS. How does the effect of H2O compare with the effect of CO2 derived from the same sources? All assumptions must be justified and calculations and sources of information must be shown.
I laughed very hard at this last one. It’s all a complete mess and meshes together many different problems. There’s absolutely no relation between what we burn for example and the absoprtion properties of water vapor or CO2 (and by the way, for CO2 you want to look near 15 microns and the unsaturated bands on either side). There’s also essentially no effect from water vapor from those sources since it precipitates out quickly and is thus not a climate forcing. This is of course in the gas phase, I’m not sure what information he wants about liquid or solid phases. All togther this is jumbled up nonsense and shows that Plimer is intentionally trying to mislead others.
For other of Plimer’s questions, I’ll let commenters tackle those. It’s unfortunate that skeptics wanted to “debate” for so long and now have this clown representing them, who is just throwing up sciency-sounding but intellectually vacuous smokescreens.