Transcript anthropogenic climate change

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Volcanic activity
Photosynthesis
Prehistoric humans
Changes in the
earth’s orbit
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The #1 cause of rising GHG levels is…
1. CO2 from
deforestation
2. CFCs from industrial
activity
3. CO2 from burning
fossil fuels
4. Methane from cows
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The #2 cause of rising GHG levels is…
1. CO2 from
deforestation
2. CFCs from industrial
activity
3. CO2 from burning
fossil fuels
4. Methane from cows
55%
36%
9%
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T/F: Scientists know that Hurricane
Katrina resulted from climate change
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2. False
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Basics
• Climate is “average weather” – Long-term
changes in temperature, precipitation, ocean
acidification, etc.
• So climate change is changes in “average
weather”…
• …and anthropogenic climate change is
changes in “average weather” due to human
activity.
Basics
• The Intergovernmental Panel on Climate
Change (IPCC) is a group of scientists and
governments created in 1988 by the World
Meteorological Organization (WMO) and the
U.N. Environment Programme (UNEP).
• Mandate: “to provide the decision-makers
and others interested in climate change with
an objective source of information...”
• “The IPCC does not conduct any research…”
Historic climate
Source: http://www.globalwarmingart.com/wiki/Image:Ice_Age_Temperature_Rev_png
Historic climate
Source: IPCC 2007, Fig 6.3
Historic climate
• Do we have a theory about what caused
historic climate changes?
• Yes: The theory is that they were driven by
variations in the Earth’s orbit (the 120,000year “Milankovitch cycles”) plus feedbacks.
• IPCC: “The next large [change], similar to
those that started past Ice Ages, is due to
begin in 30,000 years.” [IPCC 2007, FAQ 6.1]
Historic climate
Source: IPCC 2007
Energy balance
• Think of the Earth like a water heater: Energy
comes into it (Ein, e.g., from electric coils) and
energy leaves (Eout, e.g., heat loss).
• In steady state, energy in equals energy out
(Ein = Eout) and so temperature T is constant.
• Wrap a blanket around the tank and Eout goes
down. Q: What happens next?
• A: Either you can keep the same T by reducing
Ein or T rises to a new steady state.
Recent climate
Source: http://www.globalwarmingart.com/wiki/Image:Instrumental_Temperature_Record_png
Recent climate
Source: IPCC 2007, Fig 6.10
Recent climate
Source: http://www.globalwarmingart.com/wiki/Image:Mauna_Loa_Carbon_Dioxide_png
Recent climate
Source: IPCC 2007, Fig SPM.1
Recent climate
Source: IPCC 2007, Fig SPM.1
Recent climate
Source: IPCC 2007, Fig SPM.1
Recent climate and historic climate
Source: IPCC 2007, Fig 6.3
Recent climate
• Do we have a theory about what caused recent
climate changes?
• Yes: The theory is that they are driven by
anthropogenic activity (burning fossil fuels,
deforestation, etc.) plus feedbacks.
• IPCC 2007: “Most of the observed increase in global
average temperatures since the mid-20th century
is very likely due to the observed increase in
anthropogenic greenhouse gas concentrations.”
Greenhouse gases
• Most incoming energy
is at wavelengths in
the visible spectrum.
• Most outgoing energy
is at longer infrared
wavelengths.
• Greenhouse
gases(water vapor,
CO2, …) interact with
outgoing (infrared)
but not incoming
Arrhenius (Swedish chemist), 1896
Anthropogenic climate change / global warming
• Like an extra blanket on the water heater,
increased levels of CO2 and other greenhouse
gases reduce Eout (energy out).
• Since Ein (energy in) is not changing much, we
have Ein > Eout and so the Earth is out of energy
balance and so T rises.
• Q: What happens to temperatures in the
stratosphere (up 10-50km / 6-31miles)?
• A: Stratospheric temperatures are falling.
• Q: How sure are scientists about anthropogenic
climate change?
1990 (1st Assessment Report)
“[The observed warming in the 20th century] is
broadly consistent with predictions of climate
models, but it is also of the same magnitude as
natural climate variability. Thus the observed
increase could be largely due to this natural
variability…”
1995 (2nd Assessment Report)
“The balance of
evidence suggests a
discernable human
influence on global
climate.”
2001 (3rd Assessment Report)
“There is new and
stronger evidence…
most of the observed
warming over the last
50 years is likely to
have been due to the
increase in
greenhouse gas
concentrations.”
2007 (4th Assessment Report)
“Most of the observed
increase in global
average temperatures
since the mid-20th
century is very likely
due to the observed
increase in
anthropogenic
greenhouse gas
concentrations.”
Recent climate
• IPCC 2007: “Most of the observed increase in global
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average temperatures since the mid-20th century
is very likely due to the observed increase in
anthropogenic greenhouse gas concentrations.”
Q: Are there other (natural) forces at work?
A: Yes, e.g., Ein from the sun has been going up.
But this is about 1/10th of anthropogenic impacts.
Q: Can other theories explain recent climate?
A: No.
Source: IPCC 2007, FAQ 9.2, Fig 1
Roy Ruffin and Paul Gregory, Principles of
Microeconomics, 7th ed. (2001), p. 380.
Brian Walter and David Salt, Resilience
Thinking (2006), p. 7.
Future climate
• Two main uncertainties about future climate.
• Uncertainty #1: What’s going to happen with
emissions of CO2 and other GHGs?
• Uncertainty #2: What’s going to happen with
positive or negative feedback loops?
• Positive feedback loops amplify. Ex: as T rises, less
snow/ice, lower albedo means more sunlight is
absorbed rather than reflected.
• Negative feedback loops tone down. Ex: As T rises,
more water vapor, so more clouds, and clouds
reflect incoming sunlight. (Note: Clouds are key!)
Climate sensitivity: How much would T go up in
a new steady state with doubled CO2?
Source: UW atmospheric physics professor Marcia Baker
Future climate
• Two main uncertainties about future climate.
• Uncertainty #1: What’s going to happen with
emissions of CO2 and other GHGs?
• Uncertainty #2: What’s going to happen with
positive or negative feedback loops?
• Positive feedback loops amplify. Ex: as T rises, less
snow/ice, lower albedo means more sunlight is
absorbed rather than reflected.
• Negative feedback loops tone down. Ex: As T rises,
more water vapor, so more clouds, and clouds
reflect incoming sunlight. (Note: Clouds are key!)
Future GHG emissions: Going up for now…
Source: IPCC 2007, Fig. SPM.3
Put Uncertainties #1 and #2 together…
Source: IPCC 2007, Fig. SPM.5. Warming is relative to 1980-1999
Future climate
• T has been rising ≈0.2°C (≈0.5°F) per decade.
• Even if we stopped cold turkey, some 21st century
warming (≈0.6°C, ≈1.1°F) is projected because
we are not in energy balance.
• Atmospheric concentrations of CO2 (280ppm preindustrial, 379ppm in 2005) are going up about
2ppm per year. [IPCC 2007 WG1SPM, p. 2]
• “For the next two decades a warming of about
0.2°C per decade is projected…” [IPCC 2007]
Recent climate
Source: http://www.globalwarmingart.com/wiki/Image:Instrumental_Temperature_Record_png