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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? |
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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 |
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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? |
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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 |
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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. |
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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 |
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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. |
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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. |
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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. |
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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. |
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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. |
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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. |
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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. |
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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. |
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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. |
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