The Science of Climate
Change
Scientific Consensus, New
Research Directions, and
Implications for Policy
Prof. Alex Hall
UCLA Department of Atmospheric and
Oceanic Sciences
SCIENTIFIC
CONSENSUS
Data: Surface Warming
Global mean surface warming 1900 to 2000: 0.6 °C
(IPCC 2001, Jones et al. 1999)
Mann et al. 1999
CO2 isn’t the only
human-related factor
affecting climate.
Slightly less than half
the human
enhancement of the
greenhouse effect is
caused by other gases,
including methane and
nitrous oxide. Also,
aerosols have a large
and difficult to quantify
impact on climate.
Computational grid of a general circulation model
This is the typical
resolution of a
climate model. Note
that there are many
important processes
for climate (such as
those related to
cloud), that cannot
be resolved explicitly
on such a coarse
grid. Note also that
the most relevant
climate impacts are
not simulated at this
resolution.
Modeled and Predicted Temperatures
Tett et al., 1999
IPCC Third Assessment Projections
IMPACTS
SURFACE ALBEDO FEEDBACK
Increase in
temperature
Increase in
incoming
sunshine
Surface albedo feedback
is thought to be a
positive feedback
mechanism. Its effect is
strongest in mid to high
latitudes, where there is
significant coverage of
snow and sea ice.
Decrease in
sea ice and
snow cover
A climate model projection of 2090 North America
Northern hemisphere snow cover is decreasing.
(Armstrong and Brodzik 1999). The rate is equivalent to
losing an area the size of California every 7 years.
Arctic researchers see early warming signals
1979
2000
Based on satellite data, these images show Arctic sea ice. The
ice cover shrunk by 9 percent a decade over that time.
CGCM projects major changes in NH sea ice
extent
1938
Loss of Mountain Glaciers
1981
Grinnell Glacier
Glacier National Park
Mountain glaciers
all over the world
are in retreat.
This is the Qori
Kalis glacier in
Peru in 1978.
Here is the same
glacier in the year
2000. The lake covers
10 acres.
From space, we can monitor the extent of melting of
the world’s major ice sheets. Greenland has
experienced a large increase in melting over the past
few decades. Images courtesy of Konrad Steffen and
Russell Huff, CIRES, University of Colorado at Boulder
There are two main global effects associated with
climate change:
(1) An increase in global mean temperature, which we
have discussed already.
(2) An increase in evaporation everywhere, driven by
increased greenhouse gas concentrations and
increased temperatures. The increase in evaporation
also implies an increase in precipitation, because the
atmosphere can’t store water vapor indefinitely. There
is no clear consensus on how the increase in
precipitation will be distributed. However, we do know
that it will not be distributed uniformly. This increase in
evaporation and precipitation is known as the
intensification of the hydrologic cycle.
Mid-Century
Precipitation
The change in
distribution of
precipitation will have a
significant effect on
total biomass. This of
course will also affect
species composition
and diversity
significantly. Some of
these effects can be
estimated by coupling
vegetation models to
global climate models
during climate change
experiments. This plot
shows the change in
simulated total live
vegetation (biomass)
between last decade of
the 21st century and
1961-1990 from two
different climate models
(Bachelet et al. 2001)
One easily anticipated effect of climate change is species migration to
higher latitudes. For example, a warmer climate may have significant effect
on forests composition. Decidous forests will probably move northwards and
to higher altitudes, replacing coniferous forests in many areas. Some tree
species will probably be replaced altogether, jeopardizing biological diversity.
Changes in Vegetation Distribution
2070-2099, relative to 1961-1990
HadCM3-A1
HadCM3
higher
HadCM3-A1
HadCM3-B1
HadCM3-B1
HadCM3
lower
PCM-A1
PCM-A1
PCM
higher
PCM-B1
PCM-B1
PCM lower
Alpine/Subalpine Forest
Alpine/Subalpine Forest
Evergreen Conifer Forest
Temperature-Evergreen Conifer Forest
driven
Mixed Evergreen Forest
Mixed Evergreen Forest
Mixed Evergreen Woodland
Mixed Evergreen Woodland
Grassland
Fire-mediated
Grassland
Shrubland
Shrubland Desert
Desert
-100
-50
0
50
100
Change in Total Cover (%)
-100
Source: A Luers/Union of Concerned Scientists
-50
0
50
Change in Total Cover (%)
100
About 2/3 of the observed sea level rise is probably
attributable to thermal expansion of seawater; the
remainder is due to melting of glaciers
CURRENT AND
FUTURE
DIRECTIONS
annual
april
significance
temperature
increase
snow
loss
Regional climate modeling is a promising approach
to give detail necessary to discuss impacts.
Diminishing Sierra Snowpack
% Remaining, Relative to 1961-1990
Lower Emissions
Source: A Luers/Union of Concerned Scientists
Higher Emissions
Decreasing Wine Grape Quality
Temperature Impacts
1961-1990
Current
Conditions
Wine Country
Cool Coastal
Northern Central
Valley
2070-2099
LOWER
LOWER
(B1)
EMISSIONS
HIGHER
HIGHER
(A1fi)
EMISSIONS
PCM
PCM
HadCM3
HadCM3
Optimal
Impaired Marginal Impaired Impaired
(mid)
Optimal Optimal Optimal Optimal
(mid-high) (mid-high) (high) Impaired
(low)
Marginal Impaired Impaired Impaired Impaired
Wine Country (Sonoma, Napa Counties)
Cool Coastal (Mendocino, Monterey Counties)
Northern Central Valley (San Joaquin, Sacramento Counties)
Source: A Luers/Union of Concerned Scientists
Regional climate and ecosystem modeling at UCLA
A view of the Santa
Anas from space,
taken by the Multiangle Imaging
SpectroRadiometer
(MISR) on February
9, 2002.
The winds simulated by the model during the Santa Ana event of February 9-12,
2002.
Note the intense flow, reaching speeds on the order of 10 meters per second,
being channeled through mountain passes.
Oct 17, 2003 MISR
STRATEGY
US CO2 Emissions from Fossil
Fuel Combustion
CREATING CHANGE
International, National, or Local?
Public Opinion
Science Research
Interest Groups