Murry Salby/2013-04-18 Hamburg

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About

Murray Salby's lecture in Hamburg on April 18, 2013 lasted a little over an hour and was video-recorded.

Notes

  • 3:55 The recent interpretation of climate revolves about changes of atmospheric composition.
    • It rests on three pillars:
      1. proxy evidence of past atmospheric composition
      2. modern changes - those actually observed
      3. simulation of their impact by climate models

Proxy Evidence

  • The proxy evidence relies on air bubbles embedded in ice, sampled as cores.
  • CO2 proxy record indicates changes of 100 ppmv on a time-scale of 100ky, with smaller changes on shorter timescales
  • methane proxy record mirrors the CO2 proxy record
  • temperature proxy record also mirrors the CO2 proxy record; varies by about 8°K over the glaciation cycle
  • These ancient compositional changes are the linchpin of modern interpretation. They are the reference against which actually observed changed in the 20th century appear unprecedented. Their importance is recognized by the IPCC.
  • 5:53 He quotes the IPCC as saying, in 2007: "The mechanistic explanation of these CO2 variations remains one of the major unsolved questions in climate research." (confirmed)
  • 6:00 "The coherence -- that is, the codependence -- between atmospheric composition and temperature is dominated by the cyclic swing over 100ky, but their coherence is not unique to the glaciation cycle." Filtering the data for periods shorter than 50ky (removing the glaciation cycle), you still see a high correlation. (Chart at 6:26.) "What remains is broadband variability. CO2 evolves coherently with temperature over a wide range of time scales. Their coherence in the proxy record is universal."
  • 6:58 Graph: cross-correlation of CO2 and temperature proxy records, as a function of lag.
    • CO2 and temperature are strongly interdependent.
    • The correlation maximizes at a small positive lag, with CO2 changes following temperature by less than a thousand years.
  • 7:41 Graph: Coherence spectrum, as a function of frequency
    • CO2 and temperature evolve coherently on all timescales longer than 10ky.
    • Dotted line shows phase spectrum (relative timing) between CO2 changes and temperature changes. "The phase hovers near zero" (but always below, though he doesn't mention this).

Observed Evidence

  • 8:53 Graph: observed record. 1960-2010
  • 9:05 Graph: cross-correlation of CO2 and temperature observational records, as a function of lag
    • Changes in CO2 peak about 10 months after changes in temperature.

CO2 Change

  • "CO2 is produced and destroyed at the Earth's surface -- but in the atmosphere, it's conserved."
  • "Its rate of change, and CO2 mixing ratio "R", must therefore equal net emission from the Earth's surface."
  • 9:57 Figure: drCO2 / dt = Net Emission = "the rate of increase of CO2"
  • 10:25 Graph: Net Emission of CO2, 1960-2010
    • Unlike human sources, native (natural) sources are inherently sensitive to surface conditions.
    • "Field measurements reveal that native emission of CO2 depends strongly on temperature."
  • 10:49 Graph (based on 10:25): Global surface temperature, 1960-2010
    • "CO2 emission tracks the history of surface temperature" with a correlation of 0.63.
    • "The correspondence holds even for systematic changes during the last half-century, when net emission intensified by 100% from 1 ppmv per year to 2 ppmv per year."
    • "The observed relationship means that the leading order, the rate of change of anomalous CO2 -- the departure from its mean -- is proportional to anomalous temperature."
    • 11:30 Figure: drCO2 / dt = γ(Te − TeO) "where γ is sensitivity to temperature of CO2 emission"
    • "CO2 must therefore evolve like the integral of temperature", i.e. temperature "must then be proportional to the cumulative net emission of C02".
    • 11:47 Figure (based on 11:30): integral equation for above statement
    • "CO2 then evolve coherently, as in the proxy record, but now they evolve in quadrature."
      • 12:34 Figure (based on 11:47): two more equations, and graph showing what he means by "quadrature"
      • If temperature evolves like cos(time), CO2 must evolve like sin(time) "lagging temperature by a quarter cycle".
      • 12:52 "More generally, the evolutions of CO2 and temperature can be expressed through Fourier integral as a synthesis of such spectral components: For each frequency ω, the complex amplitude of mixing ratio, R(ω), lags the complex amplitude of temperature, T(&omega), by 90 degrees - or a quarter cycle."
    • "As different spectral components in these integrals have different periods, no single lag will simultaneously align all components. Covariance between CO2 and temperature must therefore be distributed widely over positive lag – as was observed."
    • 13:51 Graph: Coherence Spectrum (observed record)
      • "Temperature and CO2 evolve coherently on all time-scales longer than a couple of years."
    • 13:58 Graph (based on 13:51): dotted line now shows phase: "It hovers near -90°."
      • (Actually, it goes between ~-40° and -90° and spends a bit more time at the latter, but the distinction may not be significant.)
      • This is more confirming evidence that the two "evolve in quadrature".

Part 4

Outlinks

Recordings

Discussion - favorable

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