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Eine Kleine Nachtphysik

(or a little physics about climate change. Or at least a few clarifications about some of the points being raised.)

Duty Calls: xkcd

In the wake of Climategate, a wide variety of mistakes and misapprehensions are being circulated on the Internet (as if that weren’t happening before).

For example, in this article from the Telegraph:

Phil Jones, the 57-year-old director of the CRU, is the man who has suddenly found himself the number one target of climate change conspiracy theorists the world over after he sent the most damaging of all the emails exposed by the anonymous hacker.
In one message, dated November 1999, he wrote: “I’ve just completed Mike’s trick of adding in the real temps to each series for the last 20 years (ie from 1981 onwards) and from 1961 to hide the decline.”
Gotcha! say the global warming sceptics who have argued for years that average temperatures on Earth are, in reality, either stable or going down. Professor Jones defended himself by claiming the word “trick” was used out of context and simply referred to a legitimate method of handling data.

Well, actually not. “Hide the decline” had nothing whatsoever to do with the flattening of GMST (global mean surface temperature) post-2000, since that was written in 1999. It had to do with what is technically called the “divergence problem”, which is that the tree-ring data used in paleoclimate studies (such as the “hockey stick”) don’t match real, measured, temperatures in recent decades. The reason Jones would want to hide that is that if tree rings don’t register the current hot spell, they might have missed past hot spells as well, and thus couldn’t be used as proof that the current warming was unprecedented.

There are a bunch of other misapprehensions floating around, on both sides of the question. Here’s a grab bag.

  • The greenhouse effect doesn’t exist, or is negligible because CO2 is a trace gas, etc. (Found on some of the more argumentative “denier” sites). Try drinking a glass of water with 388ppm botulin toxin and then tell me about trace concentrations. The greenhouse effect is pretty well understood physics.
  • There’s some “tipping point” inherent in the greenhouse effect (found on the more argumentative alarmist sites). Nope, the well-understood greenhouse effect gives a logarithmic increase in temperature with added CO2. That is, if increasing CO2 from 194 to 388 increased temperatures one degree, increasing it from 388 to 776 would get us one more degree, and from 776 to 1552 would produce just one more degree after that. This is why the discussion is typically framed in terms of “a doubling of CO2.”
  • The earth isn’t really warming, or the warming has stopped. Nope, there really was a “Little Ice Age” and temperatures have been rising for as long as we’ve measured them. If you want to look at data and do a little of your own analysis, Paul Clark’s “Wood for Trees” site is marvelous. It gives access to a number of datasets and an easy-to-use web-based analysis interface. Here it is doing a linear regresion on the longest measured record, HADCRUT. There’s a secular (long-term) rise of about 0.44 degrees per century. On the other hand, it’s clear that there’s a roughly 60-year cycle about that trend and a lot of the rise from the 70′s thru the 90′s was cyclic rather than secular. There are almost certainly lower-frequency cycles as well.
  • Data adjustment by the climatologists has hugely skewed the record. Here’s the HADCRUT record plotted against the satellite record, which doesn’t have those problems. You don’t own a thermometer that could tell the difference. Not that there wasn’t some hanky-panky, but the difference is probably due as much to the different proportions of land vs sea measurements than anything else.
  • Computer models of climate are worthless. No, they do reasonably well in the regimes they’ve been tuned for. They tracked the rise in GMST up through 1998, which is one reason they developed so much credibility over that period.
  • Computer models are valid forecasters on century-long scales. The arguments for this are as follows: Yes, we know that the actual weather is chaotic and the models can’t track it, but climate can be thought of as the basin of attraction that the weather moves in, and if the model captures the basin of attraction properly, the weather in the model will show us what the overall climate will be like. But just one decade after the GMST inflection point of 1998, the models are pushing the envelope of 95% confidence intervals:

    (btw, Lucia is oneof the best mathematically sophisticated, balanced bloggers out there (recognized as a “lukewarmer”, i.e. someone between the extremes of the debate, by both sides).
    It’s debatable whether the models fail statistical confidence tests as of even date. But the fact that they are so close to the edge so soon doesn’t inspire confidence that they have a basin of attraction that matches the one of the real Earth for a full century. Specifically, it seems likely that they have too high a parameter for cloud-based feedback and thus overestimate the temperature sensitivity as a function of CO2.
    This is probably the one case where the leaked emails should actually change anyone’s perception of the science; Kevin Trenberth, in 1255523796.txt:

    How come you do not agree with a statement that says we are no where close to knowing where
    energy is going or whether clouds are changing to make the planet brighter. We are not
    close to balancing the energy budget.

    I have some personal experience trying to balance energy budgets in massive semi-empirical simulation codes, and I have lots of sympathy for the modellers. But my experience also tells me that the models are very unlikely to have been validated and tuned well enough to make reliable century-scale predictions.

So what does this all mean, bottom line? Not an awful lot — but just take all those claims you hear, on both sides, with a grain of salt.

2 Responses to “Eine Kleine Nachtphysik”

  1. Paul Clark Says:

    Hi,

    Thanks for the links and kind words, and a nice balanced viewpoint for once!

    Just one comment: You compare HADCRUT3 and the satellite record, but the graph on WFT you point to is actually using WTI – that’s my average of all four temperature sources and hence includes HADCRUT3 (and GISTEMP) already. Also, WTI is rebased to the satellite baseline, so you’re actually showing the small baseline difference (0.15K), which actually makes it look *more* different than it is!

    I think the fairest comparison is probably with RSS (with baseline adjustment):

    http://www.woodfortrees.org/plot/rss/plot/hadcrut3vgl/from:1979/offset:-0.15

    which makes them look even more identical. Which means, as you say, whatever else is/was going on at CRU, significant changes to the global trend over the last 30 years isn’t one of them.

    Best wishes

    Paul

    P.S. That’s one of my favourite cartoons, too :-)

  2. Arnold Williams Says:

    If you get into the raw data, it appears that 75% of the globe has not seen significant warming. I know that his post references a lot of raw numbers, and his other posts require math to keep up with, but it’s worth it.

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