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Friday round-up

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Blogging has been a little light recently (apologies!), but here are a few pieces that have caught our eye this week.

First up, the Columbia Journalism Review has a two–parter on journalistic coverage of climate change inspired by comments from Jeff Huggins on the Andy Revkin’s Dot Earth blog. The key issues CJR addresses are familiar ones to readers here: how to communicate mainstream science in a way that doesn’t distort the reality of the consensus on many issues in favour of controversy on more cutting-edge topics. Definitely worth a read, and proof (if such were needed) that commenting on blogs can make a difference to coverage.

Next, the role of CO2 as a long-term climate forcing. The old CO2 lead/lag issue keeps making the rounds as a contrarian talking point (and made a brief resurgence here in comments this week) despite the fact that the existence of impact of climate on the carbon cycle in no way invalidates the impact of CO2 (as a greenhouse gas) on climate. However, there is a nice paper in Nature this week (Lunt et al, 2008) which looks at the various proposed triggers for the onset of the quaternary glaciations at the end of the Pliocene (~3 million years ago). These triggers involve, permanent El Nino events, the closing of the Isthmus of Panama, changes in orbital forcing, tectonic uplift of the Rocky mountains – and long-term decreases in CO2 as a function of very slow variations in sea floor spreading and chemical weathering. Lunt et al find that only the change in CO2 (400 ppm to 280 ppm) can explain the changes in the ice sheet. None of the other ideas come even close.

Thus, it looks very much like the climate changed radically due to this externally forced drift in CO2 (and tectonic is external for climate purposes on this timescale). As a corollary, this is an expansion of the idea we discussed a few months back, that the long term changes in the Earth system due to external forcings might be well be larger than the classical (Charney) sensitivity we often talk about.

Third. There has been a lot of discussion on energy futures in the comments – Nature had a good rundown of the scientific constraints on the different prospects. But this video is a quite entertaining discussion of why we just can’t get our heads around the issue from Dan Gilbert (h/t GH).

Finally, a commentary on the prospects for continued employment as an Arctic ice expert (h/t Climate Feedback).

Once more unto the bray

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We are a little late to the party, but it is worth adding a few words now that our favourite amateur contrarian is at it again. As many already know, the Forum on Physics and Society (an un-peer-reviewed newsletter published by the otherwise quite sensible American Physical Society), rather surprisingly published a new paper by Monckton that tries again to show using rigorous arithmetic that IPCC is all wrong and that climate sensitivity is negligible. His latest sally, like his previous attempt, is full of the usual obfuscating sleight of hand, but to save people the time in working it out themselves, here are a few highlights.

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Aerosols, Chemistry and Climate

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Everyone can probably agree that the climate system is complex. Not only do the vagaries of weather patterns and ocean currents make it hard to see climate changes, but the variability in what are often termed the Earth System components complicates the picture enormously. These components – specifically aerosols (particulates in the air – dust, soot, sulphates, nitrates, pollen etc.) and atmospheric chemistry (ozone, methane) – are both affected by climate and affect climate, since aerosols and ozone can interact, absorb, reflect or scatter solar and thermal radiation. This makes for a rich research environment, but can befuddle the unwary.
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More PR related confusion

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It’s a familiar story: An interesting paper gets published, there is a careless throwaway line in the press release, and a whole series of misleading headlines ensues.

This week, it’s a paper on bromine- and iodine-mediated ozone loss in marine boundary layer environments (see a good commentary here). This is important for the light that it shines on tropospheric ozone chemistry (“bad ozone”) which is a contributing factor to global warming (albeit one which is about only about 20% as important as CO2). So far so good. The paper contains some calculations indicating that chemical transport models without these halogen effects overestimate ozone near the Cape Verde region by about 15% – a difference that certainly could be of some importance if it can be extrapolated across the oceans.

However, the press release contains the line

Large amounts of ozone – around 50% more than predicted by the world’s state-of-the-art climate models – are being destroyed in the lower atmosphere over the tropical Atlantic Ocean.

(my highlights). Which led directly to the headlines like Study highlights need to adjust climate models.

Why is this confusing? Because the term ‘climate models’ is interpreted very differently in the public sphere than it is in the field. For most of the public, it is ‘climate models’ that are used to project global warming into the future, or to estimate the planet’s sensitivity to CO2. Thus a statement like the one above, and the headline that came from it are interpreted to mean that the estimates of sensitivity or of future warming are now in question. Yet this is completely misleading since neither climate sensitivity nor CO2 driven future warming will be at all affected by any revisions in ozone chemistry – mainly for the reason that most climate models don’t consider ozone chemistry at all. Precisely zero of the IPCC AR4 model simulations (discussed here for instance) used an interactive ozone module in doing the projections into the future.

What the paper is discussing, and what was glossed over in the release, is that it is the next generation of models, often called “Earth System Models” (ESMs), that are starting to include atmospheric chemistry, aerosols, ozone and the like. These models may well be significantly affected by increases in marine boundary layer ozone loss, but since they have only just started to be used to simulate 20th and early 21st Century changes, it is very unclear what difference it will make at the large scale. These models are significantly more complicated than standard climate models (having dozens of extra tracers to move around, and a lot of extra coding to work through), are slower to run, and have been used much less extensively.

Climate models today are extremely flexible and configurable tools that can include all these Earth System modules (including those mentioned above, but also full carbon cycles and dynamic vegetation), but depending on the application, often don’t need to. Thus while in theory, a revision in ozone chemistry, or soil respiration or aerosol properties might impact the full ESM, it won’t affect the more basic stuff (like the sensitivity to CO2). But it seems that the “climate models will have to be adjusted” meme is just too good not to use – regardless of the context.

Freeman Dyson’s selective vision

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In the New York Review of Books, Freeman Dyson reviews two recent ones about global warming, but his review is mostly shaped by his own rather selective vision.

1. Carbon emissions are not a problem because in a few years genetic engineers will develop “carbon-eating trees” that will sequester carbon in soils. Ah, the famed Dyson vision thing, this is what we came for. The seasonal cycle in atmospheric CO2 shows that the lifetime of a CO2 molecule in the air before it is exchanged with another in the land biosphere is about 12 years. Therefore if the trees could simply be persuaded to drop diamonds instead of leaves, repairing the damage to the atmosphere could be fast, I suppose. The problem here, unrecognized by Dyson, is that the business-as-usual he’s defending would release almost as much carbon to the air by the end of the century as the entire reservoir of carbon stored on land, in living things and in soils combined. The land carbon reservoir would have to double in size in order keep up with us. This is too visionary for me to bet the farm on.

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Climate Change and Tropical Cyclones (Yet Again)

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By Rasmus Benestad & Michael Mann
Hurricane Katerina
Just as Typhoon Nargis has reminded us of the destructive power of tropical cyclones (with its horrible death toll in Burma–around 100,000 according to the UN), a new paper by Knutson et al in the latest issue of the journal Nature Geosciences purports to project a reduction in Atlantic hurricane activity (principally the ‘frequency’ but also integrated measures of powerfulness).

The close timing of the Knutson et al and Typhoon Nargis is of course coincidental. But the study has been accorded the unprecedented privilege (that is, for a climate change article published during the past 7 years) of a NOAA press conference. What’s the difference this time? Well, for one thing, the title of the paper: “Simulated reduction in Atlantic hurricane frequency under twenty-first-century warming conditions” (emphasis added).

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Tropical tropospheric trends

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Once more unto the breach, dear friends, once more!

Some old-timers will remember a series of ‘bombshell’ papers back in 2004 which were going to “knock the stuffing out” of the consensus position on climate change science (see here for example). Needless to say, nothing of the sort happened. The issue in two of those papers was whether satellite and radiosonde data were globally consistent with model simulations over the same time. Those papers claimed that they weren’t, but they did so based on a great deal of over-confidence in observational data accuracy (see here or here for how that turned out) and an insufficient appreciation of the statistics of trends over short time periods.

Well, the same authors (Douglass, Pearson and Singer, now joined by Christy) are back with a new (but necessarily more constrained) claim, but with the same over-confidence in observational accuracy and a similar lack of appreciation of short term statistics.
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