Transcript PPT

Many past ice ages were caused by…
Volcanic activity
Photosynthesis
Prehistoric humans
Changes in the
earth’s orbit
5. Sun spots
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Anthropogenic climate change
• Climate is “average weather” – Long-term
changes in temperature, precipitation, etc.
• So climate change is changes in “average
weather”…
• …and anthropogenic climate change is
changes in “average weather” due to
human activity.
The IPCC
• 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…”
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 are the two options for what
happens next?
• A: Either you can keep the same T by reducing Ein
(conservation!) or T rises to a new steady state.
Historic climate
(Thousands of years)
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.
Historic climate
Source: IPCC 2007
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.
• “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]
Recent climate
Source: http://www.globalwarmingart.com/wiki/Image:Instrumental_Temperature_Record_png
Temperature trends (°F per century) since 1920
cooler warmer
3.6°F
2.7°F
1.8°F
0.9°F
PNW warmed
+1.5 F during
the 20th century
Source: UW Climate Impacts Group
Puget Sound Area Air Temperature
Source: UW Climate Impacts Group
Recent climate
Source: http://www.globalwarmingart.com/wiki/Image:Mauna_Loa_Carbon_Dioxide_png
Recent climate
Source: IPCC 2007, Fig SPM.1
Recent climate and historic climate
(Thousands of years)
Source: IPCC 2007, Fig 6.3
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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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.”
Arrhenius (Swedish chemist), 1896
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
(visible).
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)?
What happens to temperatures in
the stratosphere?
1. Rise
2. Fall
50%
1
50%
2
Stratospheric temperature
• Q: What happens to temperatures in the
stratosphere (up 10-50km / 6-31miles)?
• A: Stratospheric temps are falling (IPCC 2007).
• 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
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 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
T/F: Scientists know that Katrina
resulted from climate change
1. True
2. False
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T/F: Climate change could lead to an
ice age by stopping the MOC
1. True
2. False
91%
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Future climate
• Global temperature has been rising ≈0.2°C
(≈0.5°F) per decade, and IPCC 2007 predicts
similar increases “for the next two decades.”
• 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. [IPCC 2007]
• Atmospheric CO2 concentrations (280ppm preindustrial, 379ppm in 2005) are going up ≈2ppm
per year. [IPCC 2007 WG1SPM, p. 2]
Recent climate
Source: http://www.globalwarmingart.com/wiki/Image:Instrumental_Temperature_Record_png