Future Climate Evolution Chapter 19—Part 1 Future Climate Evolution

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 

Future Climate Evolution 0 0.4 1.2 1.6 Solar luminosity Surface temperature/ atmospheric CO2 Kump et al., The Earth System (2002), Fig. 19-1

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?

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 

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

Seawater spray solution Fleets of seawater sprayers could create additional tropospheric aerosol particles that could cool the Earth by increasing its albedo http://www.treehugger.com/files/2009/09/wind-powered-yachts-sea-salt-climate-change.php

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 

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

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 http://news.cnet.com/2300-11397_3-6132879.html

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?