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.

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 (%)

After Milly et al., Nature, 2005

10-30%

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 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