Climate change: observations

1) Average Surface Temperature

There is robust evidence for a 0.8 degree increase in the global surface temperature since preindustrial times, confirmed by four independent analyses.  The ten hottest years on record all come after 1997.  Temperature measurement sites cover the globe sufficiently finely (angular separation of about one degree) to allow accurate averages.  Two objections have been raised to these results.  First, it is claimed that they may be skewed by the presence of some measurement sites in urban heat islands.  This is a legitimate concern, but it is adequately countered in the averaging process, which rejects measurements in urban areas if they disagree with neighboring rural measurements.  Besides, if one rejects urban sites altogether and uses only uncontaminated rural sites, the warming trend is stronger.  Another objection is that satellite data failed to confirm a warming trend in the mid-atmosphere over the last couple of decades.  This was indeed a notable discrepancy, but it is now generally accepted that it came from imperfections in the statistical analysis of the satellite data.  A more recent analysis incorporating both satellite and balloon data confirms mid-altitude warming.  (The stratosphere, on the other hand, has cooled significantly over the same period that the troposphere has warmed.  As we will see, this is a robust prediction of greenhouse effect models and is inconsistent with warming by an increase in solar radiation.)

Average surface temperature of the Earth (averages from direct measurements)

 In the data above, we see significant short-term variations on top of a clear overall trend.  It would thus be reckless to read too much into the apparent stall in heating over the past decade (which is still, you’ll recall, the warmest since direct measurements began).  In fact, given that solar irradiance is going through a trough, the real notable fact is that the world isn’t cooling.  (The difference in solar forcing between peak and trough is roughly the same as a little over a decade of CO2 dumping at expected rates, according to models whose veracity we will consider later.)

Solar irradiance

The most notable thing about the above curve is that it does not track the surface temperature.

2) Ocean Heating

Ultimately, ocean temperature is a far better measure of global warming than surface air temperature, since the ocean stores far more heat than the atmosphere.  The heat content of the ocean shows an unmistakable warming trend:

Ocean heat energy

 This has led to an accompanying rise in sea levels


Glaciers and ice caps are melting in many places, although regional variations are large.

Greenhouse gases

The average concentration of carbon dioxide (usually thought to be the ultimate driver behind changes in the atmosphere’s infrared opacity, i.e. increases in other greenhouse gases like water vapor are thought to be caused by heating from CO2 increase) has increased from 260-280ppm before the Industrial revolution (according to ice core measurements staying within this range for millennia) to 391 today, and rapidly increasing.  Humans emit more than enough to  account for this (indicating that carbon trapping by oceans, plants, or whatever has slightly accelerated, so that we don’t bear the full brunt of whatever the effects would otherwise be of our emissions).

Climate history

Past temperatures can be estimated indirectly from tree rings, ice core bubbles, and other markers.  However, these measurements seem to me much more uncertain than the above results.  In order to avoid diversion into unnecessary controversy, I will not discuss or refer to them.  I will also not discuss the claim, plausible but not definitely established, that global warming is or will make extreme weather phenomena more common (e.g. stronger hurricanes).


The 1970-2000 warming seems undeniable.  Even if the methodology of one of these measurements were questionable, it is quite implausible that all of them are wrong while remaining consistent with each other.  If, for example. someone thinks the surface land temperature measures are flawed or manipulated, how does he explain the ocean temperature, sea level, glacier, permafrost, upper atmosphere, etc. results, all of which corroborate the basic warming theory?

The important questions, to be addressed in successive posts, are

  1. What’s causing the warming?
  2. To what degree will warming continue in the future?
  3. How bad will the effects be?
  4. If we’re causing it, are the effects bad enough to offset the cost of stopping it?
On climate change (First Principles)

9 Responses

  1. The heat reflecting produced by cloud cover has been left out of the models because it is not well understood. What other large factors have been left out of the discussion for the same reason?
    When and how was the multiple body problem solved? In other words, since when can anyone predict the mid to long term behaviour of systems with three or more non-linear, interacting components?
    Along this line, how can we speak of “normal” climate if real world climate systems are not going to be stable over time – because of the chaos inherent in the underlying physics – regardless of what humans do?

  2. Hello Rum,

    You are right to point to the subgrid modeling of clouds as a major source of uncertainty in the models. To clarify your point, the effect of changing cloud cover on the albedo of the Earth is well understood, but there are great uncertainties in how cloud cover changes due to global warming. Changes in the infrared emission from clouds due to rising cloud tops is another big headache. I have not yet addressed the reliability of computer models (to anticipate: I don’t trust them as more than order-of-magnitude guesses), but I do think it would be reckless to just assume that the unknown effects must add up in a benevolent way. Things could be much worse than predicted.

    As for multi-body systems with nonlinear interactions, except for special cases, it will obviously never be “solved” because of extreme sensitivity to initial conditions. Run climate models with slightly different initial conditions, and you’ll get different yearly variations, and of course every one will be somewhat different from the actual record. However, the ensemble average, once equilibrium is achieved, *can be solved* because it’s just a matter of overall energy conservation. To think about it another way, the exact evolution to and around equilibrium is an initial value problem, subject to the “butterfly effect”, but the equilibrium itself is more like a boundary value problem, although we solve for it via evolutions. So the question of, say given a doubling of CO2 where will the average temp end up, is not in principle intractable. For the same reason, atmospheric chaos doesn’t prevent us from meaningfully identifying “normal” behavior.

  3. There have been, from time to time, Ice-Ages driving glaciation over wide parts of the globe… Until things changed and the glaciers melted.
    N. Africa was not an arid, desolate waste-land, until it became one.
    In Roman times, grapes were grow-able over most of England, though not now. Humans had f..k all to do with this, imho.
    As always, the real work is in figuring out the right way to valuate the importance of the various factors driving these changes..
    If there are stable boundaries appicable to the overall behavior of climate systems then this is like a boundary layer problem.
    As for me, I really do not know.
    I do think repairing the damage will be much easier than preventing it.

  4. Climate models will need to be substantially revised:

  5. Bonald – when you finish your investigation, reflect on the biasing effect of sunk costs.

    The very fact that one has invested many hours in researching something has a strong psychological tendency to make one assume there is at least *something* in it, and that a bit more work might serve to clarify things.

    But you are actually in a position analogous to a biologist in the Soviet Union during the Lysenko era – if there has been (so far) less violent coercion than in the USSR, the volume of misinformation, the pervasiveness of propaganda and the distortion of scientific discourse now is much greater than then; and the maximum, average and base-level competence of researchers involved is much lower.

    (I presume you know that the only really able and honest scientist to ‘believe’ that we can validly predict future climate warming – i.e. James Lovelock – believes that the greenhouse effect is mostly due to methane not CO2, and that it is long-since irreversible – something to be coped-with, or not, but not something preventable.)

  6. Hmmm. A long comment I left here seems to have gotten eaten. I wonder if I somehow screwed up posting it or if it went into a spam folder or something.

  7. Hi Bill,

    I checked my spam folder but didn’t find anything. Bruce has also told me that he’s had trouble posting comments. I’m concerned but don’t know how to track down the problem. Did the post have a bunch of web links in it? That sometimes triggers problems.

  8. No, it didn’t have more than a link or two. Unfortunately, I have no suggestions for you. OTOH, I’m not sure the fault isn’t with me.

  9. Sigh. You haven’t read Pournelle. Nor, judging by your sources, anybody else not Cathedral-approved – there are plenty, Orson Scott Card’s piece on Mike Mann was the one that first got me to start doing my own digging and thinking on the topic – which you evidently are too lazy or close-minded to bother with.

    This piece is too full of false assumptions and logical errors and scientific procedural errors and general crap. For the record – for just one example – the very first sentence is wrong (as are most of the others but I’m not going to bother breaking the whole thing down). There is no such thing as a measurable 0.8 degree change in global temperature. The very concept of such a measurement is nonsense. Anybody who actually learned about significant figures in high school chemistry would understand this. You don’t.

    I was going to say something about how you should at least have discussed the freezing of the Hudson during the Revolution and “The Silver Skates” and the dairy farms on Greenland and the Roman breadbasket in North Africa especially as compared to the relative stability of climactic zones from 1850 or so till now – which is to say a complete lack of correlation with industrialization and all the purported measurements you trust so blindly. Then I see this:

    “However, these measurements seem to me much more uncertain than the above results. In order to avoid diversion into unnecessary controversy, I will not discuss or refer to them.”

    This, right here, is why you are an idiot.

    Lead a horse to water, etc.

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