Milankovitch Cycles and the Earth’s Climate

Here are the slides for a talk I’m giving at the Cal State Northridge Climate Science Seminar:

Milankovitch Cycles and the Earth’s Climate.

It’s a gentle introduction to these ideas, and it presents a lot of what Blake Pollard and I have said about Milankovitch cycles, in a condensed way. Of course when I give the talk, I’ll add more words, especially about the different famous ‘puzzles’.

If you have any corrections, please let me know!

I’m eager to visit Cal State Northridge and especially David Klein in their math department, since I’d like to incorporate some climate science in our math curriculum the way they’ve done there.

4 Responses to Milankovitch Cycles and the Earth’s Climate

  1. Arrow says:

    The choice of the first picture is questionable :P

    It would be more relevant to the topic of the talk if it showed temperature instead of CO2. Also if it has to be CO2 at least the vertical scale should start at zero to give a proper overview of the situation which I think is more important in this case then the exact details of the shape (which would be somewhat compressed as a result).

    Seems like wordpress is eating up my comments :/

  2. jw98029 says:

    No mention to the direct correlation with the derivative of ice volume (Calder 1974, Roe 2006) – any comments?

  3. ar18 says:

    If you are really serious about this from a scientific point-of-view instead of math only point-of-view, try finding some flaws in the theories you are promoting. There are other theories that have just as many successful predictions and they are not popular, but science is not a democracy. Science has become heavily politicized in the last few decades, mainly due to the influence of the IPCC — who therefore also (indirectly and directly) influence what scientific research gets money or not — and which theories become popular or not.

    An example of a theory that the IPCC policed scientific community refuses to acknowledge is the sea-ice model. This theory takes into account that oceanic convection plays a huge role in climate and climate feedback mechanisms. It explains why Antarctica cooled down, then warmed down a little, then froze over for good. It also explains the Bond Cycle, Dansgaard-Oeschger and Heinrich events. Can any of the very few theorie you espouse do that? Just because it’s not popular doesn’t mean it’s wrong…and the math behind the sea-ice theory is very extensive :).

    While you are at it, try finding some serious flaws in the theories that are popular, since that is what scientific reasoning is all about in a nutshell — finding flaws. Take for example the highly politicized theory that CO2 is responsible for “global warming”. CO2 levels have risen from 280 to over 380 ppm in the last 100 years. Temperatures have coincidentally risen an average of 1.2 degrees F in that same time period. Then point out that CO2 levels rose from 180 to 280 ppm since the beginning of the last Ice Age interglaciation 15,000 years ago, yet temperatures rose an incredible 16 degrees F!! In one case 100 ppm resulted in a 16 degree rise yet in the other case 100 ppm resulted in only a 1.2 degree rise. Something is seriously wrong with the anthropomorphic caused global warming “theory”.

  4. Nathan Urban says:

    Your last paragraph contains errors of fact, as well as some implied errors of logic (by the implication that deglacial and 20th century warming can be directly compared to derive inconsistencies in the climate effects of CO2).

    1. Global temperature did not rise 16 F since the last deglaciation. 6 to 8 F is more like the right ballpark, and almost certainly not more than 11 F. You might be thinking of Greenland temperatures (where ice cores are taken), which are subject to substantial polar amplification. It’s not valid to directly compare a regional temperature rise to a global temperature rise when talking about the warming effect of CO2; you need to correct for regional variations in warming.

    2. It’s also not valid to simply compare the 20th century temperature rise for a 100 ppm increase in CO2 to a deglacial temperature rise for a 100 ppm increase in CO2, for several reasons:

    2a. Because CO2 radiative forcing is logarithmic in concentration, an increase from 180 to 280 ppm has a 45% stronger warming effect than an increase from 280 to 380 ppm.

    2b. We haven’t yet seen the full response of the system to the ~100 ppm rise of anthropogenic greenhouse gases (whereas we have seen close to the full response to the deglacial rise). If you conflate a partial transient response with the full long-term response, you underestimate the latter.

    2c. There are other forcing agents besides CO2 acting that must be taken into account in order to isolate the CO2 contribution to warming (e.g., subtracting out the 20th century sulfate aerosol and non-CO2 greenhouse forcings, or the glacial dust forcing).

    2d. The set of feedbacks acting are different. The most prominent example is the huge surface albedo amplification of warming during deglaciation due to the disintegration of the northern continental ice sheets. Those ice sheets no longer exist, nor does this particular feedback, meaning you have to subtract out its large warming effect to make a comparison to the modern effects of warming.

    There will be an analogous, but smaller, modern albedo feedback if the Greenland or West Antarctic ice sheets disappear. However, in reference to point 2b, we haven’t seen the full effect of that feedback yet. Because of its size and the transient nature of the warming response, it’s not that relevant to the 20th century warming signal; the corresponding feedback is very relevant to the deglacial warming.



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