Climate Change and the Water supply: What Will it Mean for San Diego? David W. Pierce Tim P. Barnett Climate Research Division Scripps Institution of Oceanography 30 April 2008

What climate forecasts mean

Evidence for warming

Global surface temperature

Last 1200 years IPCC 2007, Fig. 6.10

Glacier change: Patagonia

Evidence for warming:  Measured air temperature (including aloft)  Measured ocean temperature (including subsurface)  Atmosphere is more humid  Reduction in glaciers, snowpack, and permafrost  Behavior of plants and animals  “Proxy indicators”: Borehole temperatures, tree rings, corals

Is it caused by humans?

How climate change works

First described by the 3 rd Nobel Prize winner in chemistry, over 100 years ago! Greenhouse gases keep the planet about 60 o F warmer

CO2 increasing since 1957 Charles Keeling, SIO

Carbon emissions by source Courtesy P. Mote

Natural vs. Human Influences IPCC 2001, Summary Fig. 4

Natural vs. Human Influences IPCC 2001, Summary Fig. 4

Natural vs. Human Influences IPCC 2001, Summary Fig. 4

Combination of factors Meehl et al., J. Climate, 2004, as redrawn by globalwarmingart.com

SolarVolcanoes Greenhouse gasesOzone Sulphate aerosolsTotal IPCC, 2007

Observed cooling in the stratosphere IPCC 2007, Figs and 3.18

Is the warming caused by humans?  Greenhouse gasses warm the planet, and atmospheric concentrations are increasing  The gasses released by human activity can account for the increased concentration  Explains increased air temperature (including aloft)  Explains increased ocean temperature (including subsurface)  Natural factors (sun, volcanoes) can account for medieval warm period, little ice age, and 1940’s, but do not match warming since the 1950s.

What does this mean for our water supply?

"California's water system might have been invented by a Soviet bureaucrat on an LSD trip." --Peter Passell, New York Times (2/27/1991)

Reduced snowpack

Peterson, B. / U.S. Fish and Wildlife Service

Runoff Reduction by 2050 (%) After Milly et al., Nature, %

Colorado River drainage Water supply for: 27 million people 3.5 million acres of farmland Users in: 7 states 2 countries

Colorado river use… “Upper” = Wyoming, Colorado, Utah and New Mexico “Lower” = Nevada, Arizona, California Barnett and Pierce, J. Water Resources Research, 2008

Colorado river use… “Upper” = Wyoming, Colorado, Utah and New Mexico “Lower” = Nevada, Arizona, California Barnett and Pierce, J. Water Resources Research, 2008

Persistent drought  San Diego imports ~80% of its water  60% of that comes from Colorado River; 40% from Northern California Hoerling and Eischeid, Southwest Hydrology, 2007

Persistent drought  San Diego imports ~80% of its water  60% of that comes from Colorado River; 40% from Northern California Hoerling and Eischeid, Southwest Hydrology, 2007

So what is the response? 1. New desalination plant; 56,000 acre- feet/year

So what is the response? 1. New desalination plant; 56,000 acre- feet/year 2. Southern California farmers get a 1/3 cut in water

So what is the response? 1. New desalination plant; 56,000 acre- feet/year 2. Southern California farmers get a 1/3 cut in water 3. Residential and commercial water savings programs being ramped up again

Summary  First realized over 100 years ago CO 2 warms the Earth  Since then, CO 2 has been steadily accumulating due to human activity  Model predicted changes over the historical era agree with surface thermometers, ocean measurements, measured streamflow, satellites, snowpack, and balloons  We live in an arid region and are vulnerable to warming! Decrease in CA snowpack; less water available in summer; persistent drought conditions; reduced San Diego water supply More, earlier, longer heat waves More wildfires Sea level rise affects our coasts Effects on hydropower supplies Less time for salmon to reproduce