Transcript The Atmosphere - Illinois State University

Global climate change
temperature
atmospheric CO2
sea level
Climate Change
Climate = average of weather conditions over seasons,
years or decades
e.g. The climate of Illinois is "humid continental"
Depends on latitude, proximity to ocean, etc.
Climate changes over geologic time as continents drift
and as Ice Ages come and go
Studying Global Change
Geologic record: what
happened in the past
Real-time monitoring:
what is happening now
Mathematical models:
predicting the future
(also tested against the
geologic record)
What is a normal Earth Temperature?
"Snowball"
Earth
Greenhouse
Earth
What is a normal Earth temperature?
Note we are
actually way
below average for
the last 100
million years.
So why worry?
1) we were not around last time it was hot!
2) we are perturbing Earth systems much faster than most
natural processes
Temperatures: last 800,000 y
We are in an interglacial period; still have permanent ice caps (for
the moment) so technically we are still in an Ice Age.
Temperatures: last 150,000 y
Glacial-interglacial cycle is about 120,000 years
Now look at CO2 for the same period
Temperatures: last 18,000 y
Glaciers retreated from upper midwest ~10,000 years ago
Last ~8,000 years have had relatively stable temperatures
Temperatures: last 1,000 y
Vikings settled
Greenland
Vikings abandoned
Greenland
Sea temperature in Medieval times estimated ~4 ˚C warmer than today
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Medieval warming period
Temperatures: last 140 y
Not everywhere has the same temperature trend, but on
average the planet's surface is heating up
Link between CO2
and Global
Temperature ?
• CO2 in the Atmosphere
• Temperature during the
Industrial Revolution
CO2 and
climate
(Last 160,000 years).
Clearly the
"Greenhouse Effect" is
very real and acts on a
short timescale
What about other
greenhouse gases?
The
Greenhouse
Effect
• Greenhouse Gases
– Carbon Dioxide
(CO2)
– Methane (CH4)
– Nitrogen oxide (N2O)
– Chlorofluorocarbons
• Concentrations of
Greenhouse Gases –
Modern Era
Carbon Cycle
Greenhouse gases
Each greenhouse gas differs in its ability to absorb
heat in the atmosphere.
HFC's and PFC's are most heat-absorbent.
Nitrous oxide traps ~ 270 times more heat per molecule
than CO2; methane traps ~21 times more.
Greenhouse gases
Greenhouse gases are global in their effect upon the
atmosphere.
The main greenhouse gases have long residence times in
the atmosphere, and therefore accumulate over time
(unlike many local air pollutants)
Greenhouse gases are generally well mixed in the
atmosphere, so their impact is mostly independent of
where they were emitted.
Hence the emission of greenhouse gases should be
addressed on a global (i.e., international) scale.
A True Greenhouse Climate!
Recent CO2 emissions
The US currently emits ~
25% of anthropogenic
CO2, mostly from burning
fossil fuels
In 1990 the US emitted 5 billion tons
of CO2 (~20 tons per person)
CO2 emissions by country
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Some conclusions
1.
"Naturally occurring" climate change has occurred in the past
on many timescales, and will continue in the future. Several
times in the past, Earth has been hotter or colder than today
2.
Anthropogenic activities have greatly increased (and continue
to increase) the concentration of greenhouse gases in the
atmosphere
3.
In the past, high levels of CO2 (greenhouse gas) have
correlated with high temperatures
4.
So we should expect global warming to continue in the future
(noticeable on a human timescale)
Title
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Future sea
level rise
(models)
Expect about 0.5 m in
the next century.
Longer range
predictions are less
certain.