Chapter 15: Present and Future Climate Part 2—Projections for the future

The problem of global warming continues to get worse for several reasons…

1) The world’s human population continues to climb 7 Billion People (2011)

2) Additional CO 2 (~1.5 GtC/yr) is added by deforestation Satellite imagery of Amazonia

3. But, most importantly, the rest of the world is industrializing rapidly /pages/China-Shanghai-skyscrapers-1.htm

Total annual flux of CO 2 : 9.7 GtC/yr * fossil fuels 1.5 GtC/yr deforestation 11.2 GtC/yr Total * 2013 value

Where does the carbon go? ~4.5 GtC/yr to the Atmosphere ~4.5 GtC/yr dissolves in the Ocean ~2.0 GtC/yr to new forest growth and to CO 2 fertilization of existing forests

Quick Sinks for CO 2 : Plant growth --limited by nutrients, water, temperature, etc. Ocean dissolution * --limited by amount of CO 3 = because of the buffer reaction CO 2 + CO 3 = + H 2 O  2 HCO 3 - * This sink has two time scales, one for the surface ocean and one for the deep ocean Over time, these will become saturated, and will be unable to remove additional CO 2

Slow Sinks for CO 2 : Weathering reactions 1) Marine sediments (CaCO 3 ) CaCO 3 + CO 2 + H 2 O  Ca HCO 3 - approx. the top 10 cm of sediments can dissolve 2) Weathering of Silicate Rocks CaSiO 3 + CO 2  CaCO 3 + SiO 2 Rate: 0.06 GtC/year VERY SLOW, BUT HUGE CAPACITY

What happens if we burn most, or all, of our fossil fuels? How high could atmospheric CO 2 go, and how long would it take to go away? CO 2 in preindustrial atmosphere (280 ppm): ~600 Gton(C) Carbon in recoverable fossil fuels: ~4200 Gton(C) TOTAL 4800 Gton(C) 4800 = Hence, atmospheric CO 2 could increase by as much as a factor of 8: 8  280 ppm = 2240 ppm!

Long-term effects of fossil fuel burning This is approximately what happens if we burn up all the fossil fuels within a few hundred years Temperature change: Each factor of 2 gives about (2-5) o C of warming Hence, a factor of 8 increase in CO 2 could lead to (6-15) o C of warming! The Earth System (2002), Box Fig. 16-2a

Business as Usual: -- High CO 2 will saturate quick sinks -- Some excess CO 2 will persist for more than a million years The Earth System (2002), Box Fig. 16-2b

Will we avoid the next glaciation? Archer and Ganopolski, G 3 (2005) David Archer at the University of Chicago has attempted to explicitly calculate whether Earth will enter another glaciation in the next few hundred thousand years If we had not burned any fossil fuels, we might go into glaciation about 50,000 years from now We have already burned enough fossil fuel to avoid that If we burn the rest of the fossil fuel reserves, we can avoid glaciation for over 500,000 years

The preceding calculations are highly speculative, of course, because we don’t know how humans will behave in the distant future What does the IPCC project for the next few hundred years?

Future IPCC (2006) scenarios The IPCC is the Inter- governmental Panel on Climate Change

Possible Scenarios for Future Fossil Fuel Use And Resulting Atmospheric CO 2 Levels

Predicted surface temperature change over the next century IPCC 2007, Summary for Policy Makers, Fig. SPM.5

Projected surface temperatures for different IPCC scenarios IPCC 2006 report: Summary for Policy Makers

Humans (and many other mammals) are fairly close to their upper limits on temperature in parts of the world today –Human body temperature: 37 o C (98.6 o F) –Required skin temperature:  35 o C If the wet bulb temperature is >35 o C, you can’t lose heat by sweating and evaporation Proc. Nat. Acad. Sci. (2010)

Different measurements of temperature Dry bulb temperature—the temperature measured by a standard thermometer Dewpoint—the temperature at which water vapor condenses when an air parcel is cooled Wet bulb temperature—the temperature that a thermometer registers when enclosed in a wet sleeve, or sock, and spun vigorously around one’s head –This temperature is intermediate between the dry bulb temperature and the dewpoint

Sherwood and Huber, PNAS (2010) Measurements today Climate model today Climate model for 10 o C global warming Max T w Max T T

The PETM: Paleocene-Eocene Thermal Maximum Surface temperatures were ~10 o C warmer during the late Paleocene/ early Eocene Temperatures spiked sharply for about 200,000 years during the PETM Transient dwarfism of land mammals is reported during that time

What if we burn everything? (All fossil fuels burned by 2300 A.D.) Calculation by scientists at Lawrence Livermore National Laboratory Corresponding paper: Bala et al., J. Climate (2005)

Greenland ice sheet melting CO 2 held constant at 4  preindustrial value (1120 ppm) Most of the ice is gone within 2000 years Sea level goes up by about 6 m 2006 IPCC report

Effects of sealevel rise A 6-meter increase in sealevel would submerge approximately the bottom 1/3 rd of Florida We probably don’t want to allow this to happen! Global_Sea_Level_Rise_Risks_png