1. Future Climate Evolution
Chapter 19—Part 1
Future Climate Evolution

2. Future Climate Evolution
The Sun continues to get brighter at a rate of ~ 1 percent every hundred million years
This should increase surface temperatures, which in turn should cause faster silicate weathering and a corresponding decrease in atmospheric CO2 

3. Future Climate Evolution
Solar luminosity
Surface temperature/
atmospheric CO2
Kump et al., The Earth System (2002), Fig. 19-1

4. Long-term implications for habitability of Earth
500 m.y: CO2 falls below 150 ppmv  C3 plants should become extinct
900 m.y.: CO2 falls below 10 ppmv  C4 plants become extinct
1.2 b.y.: The rapid rise in surface temperature causes the stratosphere to become wet  Earth’s oceans should be lost over the next few hundred million years, and all life will go extinct
Is there any way to counteract these effects?

5. Yes! We may be able to block out part
of the light from the Sun. Ideas of this
type are referred to as geoengineering.
They have been suggested as possible
ways to deal with global warming 

6. Stratospheric aerosol injection
One geoengineering strategy is to intentionally inject sulfate aerosols into the stratosphere, mimicking a large volcanic eruption
But, the resulting uneven distribution of particles could result in massive weather disruption
Mt. Pinatubo, Philippines, 1991

7. Seawater spray solution
Fleets of seawater sprayers could create additional tropospheric
aerosol particles that could cool the Earth by increasing its albedo

8. A cleaner, if somewhat more difficult, way to reduce the flux of incoming sunlight is to build a solar shield at the Earth-Sun L1 Lagrange point 

9. Lagrange points for the Earth-Sun system
Points L4 and L5 are stable equilibria
Points L1, L2, and L3 are unstable equilibria (saddle points),but you can orbit around them at low cost
L1 is the site of NASA’s SOHO satellite
L2 is the future site of NASA’s James Webb Space Telescope (JWST) and of TPF, which I will talk about on Friday
Image from Wikipedia

10. Sunshield at L1
The idea (from J.T. Early Roger Angel) would be to build a big lens at L1 and use it to deflect some of the incoming sunlight
Probably a collection of smaller lenses, in reality (technically called a Fresnel lens)
A lighthouse beam apparatus is a common example of such a lens
Need about one trillion meter-sized lenses to offset one CO2 doubling

11. Question: How do you build a really huge array like this in space?
Answer: You mine the materials on the Moon, then launch them into space using a mass driver (an electromagnetic rail gun)
Roger Angel’s paper suggested launching them from Earth, not because it’s easier, but because he wanted it to be considered as a realistic response to global warming
Which should we do in the short term: Try to keep CO2 concentrations low, or simply offset their effect in one of these ways?