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 CO2 (~1.5 GtC/yr) is added by deforestation

Satellite imagery of Amazonia

3. But, most importantly, the rest of the world is industrializing rapidly

http://www.shanghaiphotograph.com/Shanghai-China-Skyscrapers/pages/China-Shanghai-skyscrapers-1.htm

Total annual flux of CO2:

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 CO2 fertilization of existing forests

Quick Sinks for CO2:

Plant growth--limited by nutrients, water, temperature, etc.

Ocean dissolution*

--limited by amount of CO3=

because of the buffer reaction

CO2 + CO3= + H2O 2 HCO3

-

*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 CO2

Slow Sinks for CO2: Weathering reactions

1) Marine sediments (CaCO3)CaCO3 + CO2 + H2O Ca2+ + 2 HCO3

-

approx. the top 10 cm of sediments can dissolve

2) Weathering of Silicate Rocks

CaSiO3 + CO2 CaCO3 + SiO2

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 CO2 go, and how long would it take to go away?

CO2 in preindustrial atmosphere (280 ppm): ~600 Gton(C)Carbon in recoverable fossil fuels: ~4200 Gton(C)

TOTAL 4800 Gton(C)

4800 = 8 600

Hence, atmospheric CO2 could increase by as much as afactor of 8: 8280 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)oC of warming

• Hence, a factor of 8 increase in CO2 could lead to (6-15)oC of warming!

The Earth System (2002), Box Fig. 16-2a

Business as Usual:-- High CO2 will saturate quick sinks-- Some excess CO2 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, G3 (2005)

David Archer at the Universityof Chicago has attempted toexplicitly calculate whetherEarth will enter another glaciation in the next fewhundred thousand years

If we had not burned anyfossil fuels, we might go intoglaciation about 50,000 yearsfrom now

We have already burned enough fossil fuel to avoid that

If we burn the rest of the fossilfuel reserves, we can avoidglaciation for over 500,000years

• 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?

http://www.globalwarmingart.com/wiki/Image:Carbon_Dioxide_Emissions_Scenarios_png

Future IPCC(2006) scenarios

The IPCC is the Inter-governmental Panel onClimate Change

http://www.globalwarmingart.com/wiki/Image:Carbon_Dioxide_Emissions_Scenarios_png

Possible Scenarios for Future Fossil Fuel Use And Resulting

Atmospheric CO2 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: 37oC (98.6oF)– Required skin temperature: 35oC

• If the wet bulb temperature is >35oC, 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)

Measurementstoday

Climate modeltoday

Climate modelfor 10oC globalwarming

Max Tw

Max T

T

The PETM: Paleocene-Eocene Thermal Maximum

• Surface temperatures were ~10oC 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

http://en.wikipedia.org/wiki/File:65_Myr_Climate_Change.png

What if we burn everything?(All fossil fuels burned by 2300 A.D.)

http://www.universetoday.com/am/publish/world_8_degrees_hotter.html?1112005

• Calculation by scientists at Lawrence Livermore National Laboratory• Corresponding paper: Bala et al., J. Climate (2005)

Greenland ice sheet melting

• CO2 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 1/3rd of Florida

• We probably don’t want to allow this to happen!

http://www.globalwarmingart.com/wiki/Image:Global_Sea_Level_Rise_Risks_png