He said, among other misleading statements:
Then an Ice Age occurred 450 million years ago when CO2 was 10 times higher than today.'How do I know Moore purposely misled Congress? Because I corrected him on exactly this point on Twitter a few months ago. And he simply ignored all that science.
It is true that an ice age occurred about 450 million years ago -- the Ordovician–Silurian ice age.
But little is known about CO2 levels at that time -- as I pointed out to Moore on Twitter -- and what's even more significant is that the Sun was weaker than by about 4%. And the continents were in different places, meaning the planet's albedo was very different from today.
Moore ignored all this in order to pretend that the O-S ice age means CO2 is an insignificant greenhouse gas.
The Sun's irradiance increases by about 1% every 110 million years. (See the top equation on page 4 here, or Pierrehumbert's textbook pg 12 equation 1.1.) So 450 million years ago there was about 54 W/m2 less sunlight impinging on the top of Earth's atmosphere.
That's a huge amount. By comparison, recall that anthropogenic CO2's radiative forcing is now only about 1.9 W/m2.
The continents were in places nothing like where they are today. The Earth's albedo (reflectance) would have been signficantly different.
But if the Earth's albedo then was the same as today's, 0.3, it would have taken lots of CO2 just to counteract the weaker Sun. You can calculate this easily:
(1-albedo)*ΔS/4 = CO2's RF = 5.35*ln(CO2/today's baseline CO2)
or CO2 = 1640 ppm. That's with no albedo change (unlikely), just to get the same average global temperature as today (which includes our ice sheets).
Even worse, we really don't know what CO2 levels were back then. On Twitter Moore casually tossed around the cartoon to the right:
The problem is, there is very little data from back then -- proxy data points are about 10 million years apart -- and these curves come from carbon cycle models, which are much more uncertain than, say, today's climate models.
(Carbon cycle modeling is an integral part of climate models, but also their biggest uncertainty.)
This excellent review article by Dana L. Royer of Wesleyan covers CO2-forcing during the Phanerozoic -- the last 541 million years of Earth's history.
|From Royer, Geochimica (2006). |
Today is at the far right of the horizontal axis;
intervals are 100 M yrs backwards.
The best-regarded model of this class that predicts CO2 for the full Phanerozoic is GEOCARB, which has a time-step of 10 my (Berner and Kothavala, 2001); this means that CO2 fluctuations operating at timescales shorter than 10 my may not influence GEOCARB.10 million years between time steps. A huge amount can happen in 10 million years. Look how much CO2 changed during the PETM, and that was only about 200,000 years.
By the way, the O-S ice age lasted only 0.5 M yrs.
In fact, Royer says that 4% lower sunshine means the glaciation threshold rises from 500 ppm today to 3000 ppm then. Dr. Patrick Moore completely ignored that knowledge.
So the cartoon is very misleading, without error bars in either the vertical or (especially) the horizontal direction.
Moore ignored all this. He wanted to paint a certain picture -- that CO2 is not very relevant -- and he was doing to do that with or without science.
In this case, mostly without.
These are the kind of rogues we have testifying before Congress on the most important issue of our day.
Update: SkS wrote about the O-S ice period here.