Global Warming
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How much of the global warming is
caused by Natural climate change and by human activities? |
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What is the sensitivity of Earth’s
climate to the increases of greenhouse gases (CO2 and CH4) and sulfur dioxide
(SO2)? |
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What is the projection of the future
climate change? |
Human Acticities
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The initial appearance of human
species: last 100,000 to 200,000 years |
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Development of the first civilization:
the last 10,000 years |
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The arrival and growth of the
industrial era: the last few hundreds years |
Global Warming: Natural
or Man-Made
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Global surface temperature has warmed
by 0.6°C in the last century. |
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Is the global warming caused by natural
climate change or by human activities? |
Natural Climate Changes
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Observed warming |
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0.6°C in the last 100 years. |
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Tectonic Scale |
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Cooling by 0.00002°C within 100 years |
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Orbital Scale |
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Cooling by 0.02°C within 100 years |
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Millennial Scale |
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Uncertain, but probably on the order of 0.02°C (such as the net
cooling into the Little Ice Age) |
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Solar Activities |
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May cause 0.2°C warming |
Global Warming: Is it
Man-mad?
Global Warming Due to
2xCO2
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Estimated by computer models: |
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(1) Direct Greenhouse effect: warms up global surface temperature by
1.25°C |
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(2) Water vapor feedback produces another 2.5°C warming |
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(3) Snow-Albedo feedback produces another 0.6°C warming |
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(4) Cloud feedback is uncertain. |
Clouds – A Major
Uncertainty
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How do all types of clouds (high and
low clouds) respond to global warming? |
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Possibility 1: more clouds during
global warming |
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Global warming |
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More water vapor available to form
clouds |
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More clouds |
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Possibility 2: less clouds during
global warming |
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Global warming |
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A warmer atmosphere can hold more water
vapor |
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Reduce the condensation of water vapors
to clouds |
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Less clouds |
Cooling Effects of SO2
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SO2 produced by smokestacks exceeds
natural emissions. |
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SO2 reacts with water vapor to produce
sulfate aerosols. |
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Sulfate aerosols can block solar
radiation and cool the climate. |
Sources of SO2 Emissions
SO2 Cooling and CO2
Warming
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The warming effect of greenhouse gases
may be partly cancelled by the cooling effect of sulfates produced by SO2
emission from smokestacks. |
Future CO2 Change
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Atmospheric CO2 will increase within
two centuries to levels at least two and possibly four times higher than
those that existed before humans made their influence felt. |
How Future CO2 Emission
Calculated?
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Global Population: is expected to
increase to 11 billion between 2075 and 2100 (100% increase). |
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Emission Per Person: is linked to
averaged standard of living (such as car and home heating or cooling). |
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Efficiency of Use: The hardest factor
to project. The efficiency depends on technologies. This is also the factor
that may keep carbon emissions from increasing in the future. |
Projected Carbon
Emissions
Projected CO2
Concentration
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Projecting the future CO2 concentration
is more difficult than projecting the emission levels. |
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The future concentration of CO2 in the
atmosphere also depends on how the climate system redistribute the excessive
CO2 among its carbon reservoirs (such as ocean and biosphere). |
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CO2 level in the atmosphere peaks
centuries after CO2 emission reaches its peak. |
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This is related to the fact that it
take time for ocean to remove the excessive CO2 from the atmosphere. |
Projected Temperature
Changes
CO2: Past and Future
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CO2 levels were last at the 2xCO2 value
near 7 Myr ago. |
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CO2 levels were last at the 4xCO2 value
at least before 50 Myr ago and possible since the Cretaceous greenhouse world
of 100 Myr ago. |
Temperature: Past and
Future
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CO2 emission resulting from human
activities in the next few hundred years will cause global temperature
changes that took natural forces tens of millions of years to produce. |
A 2xCO2 World (50-100
years from now)
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The 2xCo2 world likely to exit by the
year 2100 will in many ways be similar to the world exited 5 to 10 million
year ago, with less sea ice and permafrost in polar regions, few mountain
glacier, and in some regions greener deserts. |
A 4xCO2 World (50-100
years from now)
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The 4xCo2 world that may come into
existence between 2200 and 2300 would be slowly moving toward condition that
exist 50 or more million years ago, when little or no glacial or sea ice was
present on Earth, and forests grew in
the higher latitudes of the Arctic. |