Monday, February 22, 2010

"Cliff Notes" on the last 2 Million Years of Climate Change


  1. Al Gore needs this cheat sheet!

  2. Pretty easy:
    Main energy source of the planet is the sun. It's light hits the atmosphere, hits the planet, warms the planet. The warmth is emitted back from the planet. Warmth is the same as infrared light. Because of the physical attributes of CO2, CO2 deflects infrared light. This is easily proveable in a laboratory and undisputed.
    So CO2 in the atmosphere prevents infrared light to emit into space, thus warming the atmosphere.

    Now the biggest producer for CO2 is the planet itself. It produces around 770 Gigatonnes of CO2 a year. And it dissolves around 788 Gigatonnes of CO2 a year. Since we produce 29 Gigatonnes of manmade CO2 a year, 11 Gigatonnes a year get into the atmosphere. So since the industrial revolution, the concentration of CO2 in the Atmosphere has been rising. This is undisputed, too. And since this has been happening for 150 years now and CO2 emissions are accelerating every year, we are currently at the highest CO2 concentration in the atmosphere in 15 to 20 million years. Which is some time before man started to walk erect.

    If you take the first two points together the question is not "Are we warming the planet" but "How much are we warming the planet".

    So you have the surface temperature difference DeltaT, which is a product of the radiative forcing of CO2 DeltaF (the amount of infrared that doesn't get into space), measured in W/m^2 and a Climate Sensitivity Lambda, measured in Kelvin / W/m^2.

    The formula is
    DeltaT = Lambda * DeltaF

    The big question is: How big is Lambda, the climate sensitivity.

    It is undisputed that for a doubling of CO2 you get at least a 1 Degree Kelvin rise in average global temperature, due to the physical infrared-absorption characteristics of CO2, if there are no feedbacks at all (glaciers melting, clouds forming etc.).

    So the question isn't "Does man change climate with CO2" but "How much?".

    Of course there are natural changes in climate due to Milankovich cycles or similar. But these occur over way longer time periods, like thousands of years.

  3. Concerning sudden changes in climate: External Factors exist. Volcanic Activity (just look at what Pinatubo did in 1991) or Meteors come to mind.

    Abrupt changes are not too strange when you think about the Albedo characteristics of ice and snow. Ice and snow have an albedo of about 0.5, reflecting about half of the sun's rays back. 50% of the energy is absorbed, resulting in warmth. Now when ice melts, it becomes water. Water has an albedo of 0.06, absorbing 94% of the energy as warmth.

    So this effect works as a positive feedback in both directions.

    It gets colder => more ice => less energy absorption, more reflection => it gets colder.

    It gets warmer => more water => more energy absorption, less reflection => it gets warmer.

    The amount and direction of these feedbacks is currently a big question mark in climate science.
    Wikipedia lists the Climate Feedbacks nicely, stating their possible negative or positive nature.

    If a lot of positive feedbacks exist, changes can be swift and a balance can be very delicate.

  4. Explaining sudden climate shifts towards the cold: Take a look at supervolcanoes, like the one below yellowstone. If such a beast erupts, like Toba 75.000 years ago, or Taupo, around 22.600 years ago, the implications are severely for the climate.

    Toba alone is estimated to have resulted in global cooling of 3-5 degrees Celsius.

  5. Shmience: I really wish it was "pretty easy"
    It would make my "job" a whole lot easier.

    I just finished preparing a new post which details some (not all) of the reasons I don't think it is so simple: "2009 Paper: Nature Rules Climate" so please have a look and tell me what I've missed.

  6. why ice ages could be unpredictable