Tuesday, August 21, 2007

"Consensus": Wrong

For the most scientific report ever made, the IPCC sure seems to have a lot of dissent in the climate community. Just a warning -- this has some science in it. I'm making an effort at putting everything in layman's terms, so you ought to be able to follow along.

ABSTRACT. The equilibrium sensitivity of Earth's climate is determined as the quotient of the relaxation time constant of the system and the pertinent global heat capacity. The heat capacity of the global ocean, obtained from regression of ocean heat content vs. global mean surface temperature, GMST, is 14 ± 6 W yr m-2 K-1, equivalent to 110 m of ocean water; other sinks raise the effective planetary heat capacity to 17 ± 7 W yr m-2 K-1 (all uncertainties are 1-sigma estimates). The time constant pertinent to changes in GMST is determined from autocorrelation of that quantity over 1880-2004 to be 5 ± 1 yr. The resultant equilibrium climate sensitivity, 0.30 ± 0.14K/(W m-2), corresponds to an equilibrium temperature increase for doubled CO2 of 1.1 ± 0.5 K. The short time constant implies that GMST is in near equilibrium with applied forcings and hence that net climate forcing over the twentieth century can be obtained from the observed temperature increase over this period, 0.57 ± 0.08 K, as 1.9 ± 0.9 W m-2. For this forcing considered the sum of radiative forcing by incremental greenhouse gases, 2.2 ± 0.3 W m-2, and other forcings, other forcing agents, mainly incremental tropospheric aerosols, are inferred to have exerted only a slight forcing over the twentieth century of -0.3 ± 1.0 W m-2.
Ok, I'm sorry, that was a little uncalled for. It can be heady if you're not used to it.

In all seriousness: Stephen Schwartz of the Atmospheric Science Division of Brookhaven National Laboratory has used empirical data (that is, actual recorded measurements) from the 1800s onward to develop some pertinent bits of information.
  1. Time constant / heat capacity = equilibrium sensitivity.
  2. Heat capacity = 14 ± 6 W yr/(m^2 K)
  3. Time constant = 5 ± 1 year.
  4. Equilibrium sensitivity = 0.30 ± 0.14 K/(W m-2)
  5. This implies that doubling CO2 increases global temperatures by 1.1 ± 0.5 degrees C.
The time constant indicates a constant, usually denoted by τ, that solves the equation
r(∆ t)= exp(-∆t/ τ)
for time required to move from a random perturbation back to the mean position (generally described as the time to 63% of the step function). In other words, its a constant that describes how long it takes for a system to "get to normal" after a given disturbance is introduced.

Heat capacity is also known as specific heat, and is defined simply as the amount of heat or energy required to raise a specified amount by a specified temperature. Some things are easier to heat up -- the metal in a skillet vs the plastic in the handle, for instance.

Equilibrium sensitivity gives an indication to the amount of time a system requires to respond to stimuli when the magnitude of these stimuli are taken into account -- big cups of coffee take longer to heat up than small ones, and boiling water changes at a different rate than lukewarm water. So far so good.

The big picture, then, is that he's modeling the system by the laws of thermodynamics. Just as you can model your skillet over the oven by taking the specific heat and thermal conductivity of the metal, the air between the burner and the pan, and the food inside it and determine scientifically how long it takes to cook some bacon, you can give an estimate for the ocean, the sun, and the Earth's climate.

Obviously this isn't a simple process, and he literally goes on for pages about how he arrives at these figures, but the net result is a relatively simple equation: Indeed, the overarching concepts involved in both climate change and heat transfer aren't terribly complicated. Energy in, energy out.

Some things I found very interesting in his paper follow.
Estimates of the effective ocean heat capacity have previously been presented by Andreae et al. (2005) and by Frame et al. (2005), in neither instance with description of how the quantity was calculated or any statistical analysis.
This is something which the "Peer reviewed" crowd should take careful note of. Many of the values used in science are often uncorroborated and are accepted on faith in the veracity and competence of the author. In this case the author is somewhat bemused as to how to compare his data to other results because of the lack of substantiation available in the literature for others who have performed similar work.
The relaxation time constant of Earth's climate system determined from this analysis, τ = 5 ± 1 yr, is essentially the same as that given by the energy balance model in the absence of feedbacks (Sec. 3), τ0 = 5 ± 2 yr. This result would seem to be indicative of little net feedback inherent in Earth's climate system.
This commentary is significant in a few ways.
  • A short time constant indicates that if we were to stop increasing CO2 levels magically, the Earth wouldn't continue to heat up. There's no heat "[coming down] the pipe".
  • The Earth was designed well: small fluctuations in forcing variables won't send it into a deathspiral or unstable condition.
  • Feedback mechanisms such as increased water vapor, albedo and ice melting apparently don't play as much of a role as is commonly suggested.
Finally, the kicker:
...The corresponding equilibrium increase in global mean surface temperature for doubled CO2, is ∆T2× ≈ 1.1 ± 0.3 K. (These and other results are summarized in Table 3). This climate sensitivity is much lower than current estimates, e.g., the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [IPCC, 2007], ∆T2× ≈ 3 K.
He cuts the IPCC's latest estimate for the temperature change due to a doubling of CO2 in the atmosphere in half from 3K to 1.1K. 1.1K of change is well within the natural variability of the system -- even as short as 100 years ago we had temperature anomalies well in excess of -1K globally.

Al Gore and his cronies can stop trumpeting their paranoid delusional vision of global catastrophe now. For one thing its unsubstantiated in the literature: a quick glance of Schwartz' paper reveals how much raw research is still being done on global climate change with a wide degree of disagreement between studies.

Additionally, this paper reveals many of the flaws in the modeling systems the IPCC relies so heavily upon. When compared to real, recorded data the predictions simply don't match up.

Finally, this paper relies heavily upon the GISS data for global surface temperatures. As noted previously on this blog, this data set is somewhat suspect after recent amateur scientists found massive errors in normalization and recording of data. Whenever you see Hansen, et al in a climate paper, remember that the data was just fixed last week -- and has been used repeatedly in its incorrect form, which massively exaggerates upward temperature anomalies.


Fat Man said...