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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
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
How climate change works
First described by the 3rd Nobel Prize winner in chemistry, over 100 years ago!
Greenhouse gases keep the planet about 60oF 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
Solar
Volcanoes
Greenhouse gases
Ozone
Sulphate aerosols
Total
IPCC, 2007
Observed cooling in the stratosphere
IPCC 2007, Figs. 3.17 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?
http://www.publicaffairs.water.ca.gov/maps/
http://www.publicaffairs.water.ca.gov/maps/
"California's water system
might have been invented
by a Soviet bureaucrat on
an LSD trip." --Peter
Passell, New York Times
(2/27/1991)
http://www.publicaffairs.water.ca.gov/maps/
Reduced snowpack
Peterson, B. / U.S. Fish and Wildlife Service
Runoff Reduction by 2050 (%)
10-30%
After Milly et al., Nature, 2005
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 acrefeet/year
So what is the response?
1. New desalination
plant; 56,000 acrefeet/year
2. Southern California
farmers get a 1/3 cut in
water
So what is the response?
1. New desalination
plant; 56,000 acrefeet/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 CO2 warms the Earth
 Since then, CO2 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