Global Warming
Dennis Silverman
Physics and Astronomy
U C Irvine
Global Warming
• Greenhouse gases: CO2 , methane, and nitrous oxide
• Already heat world to average 60° F, rather than 0° F
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without an atmosphere
How greenhouse gases work
Increased CO2 has raised temperature 1.2° F
The present radiation imbalance will cause another 1° F
heating by 2050, even without more greenhouse gas
emissions.
Recent cleaning of air is causing the earth’s surface to be
hotter and brighter.
Stabilizing the amount of CO2 would require a reduction
to only 5% to 10% of present CO2 emissions
Definitive Evidence of Rapid 1.2° F
Temperature Rise over the Last Century
Carbon Dioxide
Concentrations
are low in glacial
periods and higher
in warmer
interglacial periods
However,
concentrations
now are higher
than at any time in
the last 450,000
years.
In the insert is the
dramatic growth
over the last 50
years.
Temperature and CO2 Correlation
700
600
Double pre-industrial CO2
500
Lowest possible CO2
stabilisation level by 2100
400
CO2 now
300
10
Temperature
difference
200
0
from now °C
–10
160
120
80
40
Time (thousands of years)
Now
100
CO2 concentration (ppm)
The last 160,000
years (from ice
cores) and the
next 100 years:
temperature (red)
tracks CO2 (green).
CO2 in 2100
(with business as usual)
Adding Climate Model Projections
for the next hundred years
(new analysis expected in Feb.)
Q: What is today’s anthropogenic Radiative Forcing ?
Temperature comparison with and without
greenhouse gases and sulphur (NCAR/DOE)
NCAR/DOE conclusions on temperature
models
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“Solar activity contributed to a warming trend in
global average temperature from the 1910s through
1930s.
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As industrial activity increased following World War II,
sun-blocking sulfates and other aerosol emissions
helped lead to a slight global cooling from the 1940s to
1970s.
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Since 1980, the rise in greenhouse gas emissions from
human activity has overwhelmed the aerosol
effect to produce overall global warming. “
Global Warming Effects
• Predicted Global Warming of 5°F will affect everyone in most
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structural aspects of society and in their costs.
We don’t realize how our present housing, business, and supply nets
are closely adapted to our current climates.
The major increase in temperature and climate effects such as
rainfall, drought, floods, storms, and water supply, will affect
farming, year round water supplies, household and business heating
and cooling energy. These may require large and costly
modifications.
Some cold areas may benefit, and some hot areas will become
unfarmable and costly to inhabit.
Recent projection: US agriculture would go up 4%, CA down 15%.
Methane production seems to have stabilized (UCI result)
It is very misleading to portray the problem as a purely
environmentalist issue which affects only polar bears, a few Pacific
islanders, and butterflies.
What can be said about the controversy?
Here are some comments.
• 17 national science academies have endorsed
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the conclusion of global warming and its manmade causes.
The Intergovernmental Panel for Climate Change
(IPCC, www.ipcc.ch ), consulting 2,500 scientists
from 130 countries, will issued a new report on
Feb. 2, after six years, which states a 90-99%
probability that warming since 1950 is human
caused.
It has also concluded a >90% probability that
temperatures will continue to rise.
What can we reasonably say about fossil
fuels and global warming?
• Global warming of 1° F has occurred in the past century.
• CO2 is a greenhouse gas and is way higher than it has
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historically been.
This is generated by human burning of fossil fuel, but
fortunately, half of that generated has been absorbed in
the carbon cycle.
Common sense, models of earth systems, and the
correlation of warming with CO2 in ice ages, indicate a
direct effect between the two.
Clearly, funding much more research on this is clearly
justified.
Since we are going to run out of cheap fossil fuel this
century, research on new energy sources, and plans to
develop them are clearly called for.
Arguments against global warming and its
man-made causes
• 1. Global warming doesn’t exist
– There is one location which hasn’t warmed
– The Antarctic ice is growing in thickness
– Michael Crichton’s State of Fear
• 2. Global warming is a natural cycle and not caused by humans
(and will go away?)
– Answer: But temperature changes must have a cause. All of the
known causes are included in the models, and human made causes
dominate. Users of this symantic out never propose a “natural” cause.
• 3. Other objections to man-made origins:
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The dip in the 50s in the temperature curve
How can ppm of CO2 have any effect
Breathing creates CO2
The temperature always fluctuates
You can’t predict next week’s weather, so how can you …
Water vapor is more important
Global Warming and Publicity
• 4. “Global warming is the greatest fraud perpetrated
against the U.S.”
– Sen. Inhofe, previous head of the Energy Committee
– It is used by climate scientists so we will fund them
• Please refer to www.realclimate.org for detailed scientific
discussions of these challenges and of recent research
publications.
• Oil and energy companies are using the same
organization to lobby against global warming as brought
you the cigarettes do not cause cancer campaign. They
are also funding the dissident scientists. See Union of
Concerned Scientists report at www.ucusa.org.
Greenhouse Gases and the Kyoto Treaty
• The treaty went into effect in Feb. 2005 to reduce greenhouse gas
emissions of developed countries to 5% below their 1990 level.
• The U.S., as the largest CO2 emitter in 1990 (36%), will not participate
because it would hurt the economy, harm domestic coal production, and
cost jobs.
• China has signed the protocol, but as a developing country, it does not have
to reduce emissions, and burns lots of coal.
• In China’s defense:
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it only has ¼ the emissions of the US per capita;
¼ of its GDP is for export;
it has significantly lowered its birth rate to one child per couple;
it is planning a large nuclear reactor program (20-30 or more);
it only has one private car per hundred inhabitants; and
half of its population earns less than $2 per day;
the new three gorges dam is equivalent to several nuclear reactors in
hydropower;
– they are asking for a 4% reduction per year in greenhouse gases but probably
will not obtain it;
– they are trying to get sources of natural gas to use instead of coal.
Comparative World CO2 Emissions
World Greenhouse Gas Emissions
Effects of the Doubling of CO2
• Doubling of CO2 projected by end of century, causing
approximately a 5° F increase in average temperature
(most rapid change in over 10,000 years)
– ~1.5 foot maximum sea level rise
– More storms and fiercer ones as illustrated by Atlantic hurricanes
in 2005 with 10° hotter Caribbean sea temperatures
– Loss of coral reefs
– Increase in tropical diseases since no winter coolness to kill
insects
– 25% decline in species that cannot shift range
– Warming expected to be greater over land
– Hot areas expect greater evaporation from hotter winds causing
drought
– In the past, half of produced carbon has gone into storage as in
the oceans.
– Heating of the surface ocean layer could stop ocean mixing and
absorption into lower layers, thus shutting off carbon absorption.
Global Warming Effects
• Global Warming is an average measure
• Local warming or climate fluctuations can be very
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significant
Arctic is 5° warmer
– Ice cap is ½ the thickness of 30 years ago
– Partly due to natural cycle, partly man caused global
warming
Antarctic is 5° warmer
– Ice shelves over the sea are melting and breaking off
and may allow the 10,000 foot thick ice sheet over
Antarctica to slide off the continent faster
– This would cause a sea level rise
Rainfall is hard to predict. It could be increased or
decreased.
Drought can partly be caused by increased evaporation
at the higher temperature.
Global Warming Predictions for 2100 for business
as usual. The average increase is 5°F. Since we
don’t live over the oceans, warming will be larger.
Worldwide Glacial Melting, causing 2/3 of
sea level rise of an inch a decade.
Global Warming effects in California
• Summer temperatures rise by 4-8° F by 2100 for
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low emission scenario: 8-15° F for higher
emissions.
Heat waves will be more common, more intense,
and last longer.
Spring snowpack in the Sierra could decline by
70-90%, as winters will be warmer.
Agriculture, including wine and dairy, could be
affected by water shortages and higher
temperatures.
More forest fires.
Tree rings show that in eras of global warming,
megadroughts of decades hit the southwest US.
CO2 Effects to Increase Over Centuries
Hasn’t yet
added in
Hurricane
Katrina in
2005
Permafrost melting by 2050 or 2080
• Depending on high or
low emissions model,
most of permafrost in
Canada, Alaska, and
Russia melt by 2050
or 2080.
Worldwide increases in the average number
of frost-free days by 2080
Sea level rise has been 2 mm/yr for 50
years, but 3 mm/yr for the last decade
Florida with a 1 meter sea level rise or
storm surge
Nile and Sea Level Rise
• At 0.5 m, 3.8 million
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population displaced
(intermediate blue).
At 1 m, 6.1 million
population displaced
(light blue).
The protective 1-10
km sand belt is
eroding due to the
Aswan dam.
Ganges River delta and 1m sea level rise in
Bangladesh. 13 million displaced and 16% of rice
production lost.
• Similar 1 m sea level
rise in China would
displace 72 million
people.
Increase in Droughts (red) from 1948 to 2002.
The fraction of global land experiencing very dry conditions
(-3) rose from about 10-15% in the early 1970s to about
30% by 2002. Almost half of that change is due to rising
temperatures rather than decreases in rainfall or snowfall.
IPCC 2007 Summary Graphs
Historical Changes in
Greenhouse Gases over
10,000 years
• CO2
• Methane
• NO2
Blue shaded bands show the range from climate models using only the
natural forcings due to solar activity and volcanoes. Red shaded bands
show the range from climate models using both natural and
anthropogenic forcings.
Global Surface Warming for This Century
Economic Climate Models, Roughly in Order
of Temperature Increases, High to Low
• A2 Growing population, regional inequities
• A1 Peaking then declining population, world equity, high
tech growth
– A1FI Fossil fuel intensive
– A1B Balance of sources
– A1T Non-fossil fuel sources
• B2 Increasing population, regional inequities, lower
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population growth than A2 and tech development than
A1
B1 Peaking then declining population, world equity, nonmaterial economy, clean solutions
U.S. Carbon emission sources