Global Climate Change Overview Michael D. Mastrandrea, Ph.D. Woods Institute for the Environment Stanford University

The Key Facts Global climate change is… unequivocal, almost certainly caused mostly by us, already causing significant harm growing rapidly, and requires global action and local solutions. Clearly a global problem, but collectively, local actions can have a huge impact

Warming is Unequivocal… 2005 was the hottest year on record; 2007 tied with 1998 for 2nd hottest; 14 hottest all occurred since 1990 This kind of picture is striking, but implies something: uniform across the planet, gradual, mainly about temperature. What’s actually happening is: nonuniform, rapid, not just about temperature, mostly harmful http://data.giss.nasa.gov/gistemp/graphs/

Average Surface T in 2001-2005 vs 1951-80 …And Not Uniform Average Surface T in 2001-2005 vs 1951-80 J. Hansen et al., PNAS 103: 14288-293 ( 2006)

Shrinking Glaciers Muir Glacier, Alaska August 1941 August 2004 NSIDC/WDC for Glaciology, Boulder, compiler. 2002, updated 2006. Online glacier photograph database. Boulder, CO: National Snow and Ice Data Center.

Surface melting on Greenland is expanding 1992 2002 2005 Source: ACIA, 2004, CIRES, 2005, Roger Braithwaite, University of Manchester (UK)

Changing Patterns of Extreme Events Major floods per decade, 1950-2000

Increasing Wildfire Risk Western US area burned Source: Westerling et al. 2006

Natural Carbon Cycle

Human Impact on the Carbon Cycle Mention fossil fuels, deforestation/land use, and cement production

Carbon Flows (2005) ATMOSPHERE 750 Gt C 379 ppm CO2 OCEANS LAND emissions from marine systems 100 Gt C per year ATMOSPHERE 750 Gt C 379 ppm CO2 emissions from terrestrial systems 100 Gt C per year absorption by marine systems 102 Gt C per year absorption by terrestrial systems 103 Gt C per year OCEANS LAND human-caused emissions: 9 Gt C per year

Increasing CO2 Concentrations

IPCC, 2007

Increasing CO2 Concentrations The Greenhouse Effect and Global Warming Life on earth is possible because the sun’s energy warms the earth and its atmosphere. As this warmth radiates back into space, a portion is absorbed by a delicate balance of heat trapping gases in the atmosphere. Naturally occurring greenhouse gases include water vapor, carbon dioxide, methane, nitrous oxide, and ozone. These gases retain heat somewhat like the glass panels of a greenhouse, and act to elevate temperatures on earth. This “greenhouse effect” is a necessary natural global mechanism. Without it, the earth’s climate would be much colder and more hostile to human life.   What has changed in the last few hundred years is the additional release of carbon dioxide by human activities. Since the beginning of the Industrial Revolution, atmospheric concentrations of carbon dioxide have increased nearly 30%, methane concentrations have more than doubled, and nitrous oxide concentrations have risen by about 15%. Why are greenhouse gas concentrations increasing? Scientists generally believe that the combustion of fossil fuels and other human activities are the primary reason for the increased concentration of carbon dioxide. IPCC, 2007

Ice Core Records

Ice Core Records Source: Hansen, Clim. Change, 68, 269, 2005.

Fingerprint Analysis Black = Observed Gold = Human and Natural Forcings Blue = Only Natural Forcings IPCC, 2007

Projected Changes in CA Summer Temperature Temperature differences emerge by 2050s and are more pronounced by 2090s 2030: 2-5 degrees 2050: 4-6 lower, 4-9 higher 2090: 3-9 lower, 8-18 higher We found higher summer temps than previously reported, incorporating better physical understanding of the system Hayhoe annual average: 2.4-3.5 deg F increase by mid-century; 4.1-10.5 deg F warming by end-C ｷ Substantial increases in both summer and winter temperature, with greater summer warming than has been previously reported. UCS UCS

Pika Species Shifting and… 1900 >7,800 ft 2004 >9,500 ft But species do not always have suitable habitat to shift to. Prime example is species that live on mountain slopes, like the Pika. Species that are sensitive to temperature conditions can only move up the mountainside as conditions get too warm for them lower down. In the Sierras, Pika were seen at 7,800 feet and above in 1900. By 2004, they were not seen below 9,500 feet, and this trend is expected to continue. The mountains rise as high as 12,000 feet, but the tallus, the rocky hillside that Pika live in, does not reach that high. The result… Strong candidate for labeling as a key vulnerability

Diminishing Sierra Snowpack Percentage Remaining, Relative to 1961-1990 Note: Based on HadCM3 model output Substantial reductions in snowpack, which is 1/2 of CA’s water storage 80% precipitation falls in winter before april, but 3/4 water use is between April and Sept. Also affects fire risk and other consequences UCS

Mitigation Adaptation

Rapidly Increasing Emissions 2006 2005 Current emissions are tracking above the most intense fossil fuel scenario established by the IPCC SRES (2000), A1FI- A1 Fossil Fuel intensive; and moving away from stabilization scenarios of 450 ppm and 650 ppm. Raupach et al. 2007, PNAS

Regional CO2 Emissions 2004 2000-2004 Growth Raupach et al., 2007