Here are the notes I took while listening to Dan Britt’s lecture.

21:00 When India collided with China, the uplift of the Himalayas resulted in greatly-increased rock weathering, which pulled 80% of the CO₂ out of the atmosphere, rending the climate very sensitive to the changes in solar input that result from the eccentricity of the earth’s orbit around the sun.

Climate results from oscillations in:

Eccentricity of the earth’s orbit around the sun, a cycle of 100,000 years;

The tilt of the earth between 21 and 24 degrees, a cycle of 41,000 years; and

Precession, which is the movement around the earth’s orbit of the time of year when the earth is closest to the sun, a cycle of 23,000 years.

Presently we are closer to the sun in the winter, producing cooler summers and warmer winters.  Cooler summers allows snow to accumulate, producing glaciation – an ice age.  Also, warmer winters tend to be snowier.

But our glaciers are nevertheless melting.  Greenhouse gases are delaying the next ice age.

It’s the interplay of these factors which, by causing variations in the amount of solar radiation which reaches the surface of the earth, causes ice ages and periods of warming.

If you put global average temperatures on a graph, you can see all of these cycles.  The net effect is known as the Milankovich cycle after the Bulgarian scientist who discovered it in the 1920s.

For the last million years, our climate has been characterized by long glacial periods and short warming periods.

Global temperature followed the path predicted by these factors until about 8,000 years ago, when agriculture was introduced.  We cleared the forests and planted crops.

And 5,000 years ago we invented rice cultivation and terracing and domesticated livestock.  Cows are a major source of methane.

In the preindustrial period we put all the carbon in 10% of the global biomass into the atmosphere, which increased the CO₂ concentration in the atmosphere from 260 parts per million (ppm) to 280 ppm.

Despite all of this, solar radiation was still declining, so that in the middle ages the climate was actually getting colder.

Starting in about 1850 we began tapping fossil fuels – first coal, then oil, then natural gas.

The pre-industrial atmosphere had about 600 billion metric tons of carbon.  (A metric ton is 2205 lb.)  By burning fossil fuels, we are presently adding about 8 billion metric tons per year.  (He doesn’t say whether that’s in addition to the agriculture and livestock contributions.)

Volcanoes are the largest natural input, at about 0.2 gigatons/year, 1/45^th of the contribution of fossil fuels.

39:30 In the short term we are heading into a period of increasing sunspot activity, and he predicts that for the next 4 or 5 years we are going to have extremely hot summers.

There has been strong warming in the last 150 years.

In 1950 we were putting out about 1.3 gigatons of carbon per year and atmospheric carbon was 310 ppm.  Now we are putting out about 9 gigatons, and it is 390 ppm.

China’s GDP has exploded.  They want the same things we do.  They are producing a gigawatt-sized coal-fired power plant every two weeks.

We are in an ice age.  Continental glaciation is very unusual.  Human action has increased atmospheric CO₂ by 25% and has stopped the currant Milankovich cycle in its tracks.  We should be seeing glacial advance, and what we are seeing is glacial retreat.

“If you don’t have continental glaciation, you don’t have Miami.”

2.5 to 6.5’ rise in the ocean by 2100.

The Greenland ice sheet will melt.  We don’t know how fast.