Transcript Greenhouse Gas Emission Scenarios

Source of much of the information and graphics for this presentation
Intergovernmental Panel on Climate Change
(IPCC)
• Birthed by United Nations
• Mandate to synthesize scientific consensus on climate change and its
impacts
• First Report 1995: Global synthesis of climate data & models and
projections of impacts
• Second Report 1998: Regional analyses of climate trends, future
climate scenarios, and impact scenarios for natural and human
systems
• Third Report 2001: 3 Working groups, 23 disciplines, 1200 scientists.
Much more actual observations of changes in climate and in
impacts. Improved climate projections. Improved “attribution”
• Fourth Report in progress - due out 2007
Research from the climate science community
over the past decade has strengthened the causal
links between observed changes in Earth’s
climate system and human activities
•IPCC 1995 (First Assessment Report)
• Global warming has occured, and it may be due to
anthropogenic greenhouse gas emissions
•IPCC 1998 (Second Assessment Report) concluded that:
– “ The balance of evidence suggests a discernable human
influence on global climate.”
•IPCC 2001 (Third Assessment Report) concluded that
– “ Most of the observed warming over the last 50 years is
likely to have been due to the increase in greenhouse gas
concentrations.”
Observed Changes in Earth’s climate
Greenhouse gases = gases that absorb and
emit infrared radiation (heat). Presence of
greenhouse gases in lower atmosphere traps heat &
raises global temperature. Durations up to 100
years. Main ones:
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Water vapor
Carbon dioxide (industry, cars, wood fires)
Nitrous oxide (fertilizing & tilling land, industry, cars)
Methane (wetlands, rice paddies, cows)
Ozone (air pollution)
Indicators of the Human Influence
on the Atmosphere during the Industrial Era
Global average temperatures are increasing with increases in CO2.
Global
Average
Temperature
The Relative Influences of Different “forcing”
Factors on Global Temperatures
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Models show warming of 1930s/40s was due to natural
factors (the sun, fig a), but warming of last 30 years was
due to humans (fig b)
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Current 380 ppm
• Clear correlation between
atmospheric CO2 and
temperature over last
750,000 years (not all shown)
• Current level of CO2 is
outside bounds of natural
variability
• Rate of change of CO2 is
also unprecedented
Source: OSTP
Climate Change Attribution:
How do climate scientist “know” that current warming is
caused by humans?
• Fingerprint in climate data
• Fingerprint in ocean temperatures & processes
• Fingerprint in ocean circulation changes
• Model simulations
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Percent of the Continental U.S. with A Much
Above Normal Proportion of Total Annual
Precipitation From 1-day Extreme Events
(more than 2 inches or 50.8mm)
Source: Karl, et.al. 1996.
Observed changes in Earth’s climate since 1860
 All are statistically significant changes
 All have been causally linked to human activities (primarily burning of oil,
coal & gas). This is called “attribution”
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Increased global mean temperature, and more heat waves
Sea level has risen by several inches
Increased global cloudiness
Warming mainly at night and during winter
Increased global rain and snowfall, and more very heavy
rain and snow days (floods and winter storms)
More frequent and more intense El Niño years
More severe hurricanes in the Atlantic
Large declines in most temperate and tropical glaciers
(30% - 60% volume loss)
Large decline in Arctic sea ice, freshening of Arctic & N
Atlantic oceans, slowing of North Atlantic conveyor belt
Climate models
Global Climate Models
• Global Climate Model: GCM
• Atmosphere-ocean general circulation models
AOGCM (coupled ocean and atmosphere models)
• Regional Models - higher resolution than GCMs
Other terms
• Ensemble = often means many simulations done w/same
model & same forcing, but different initial conditions
• Or, can mean taking the mean (average) of many different
model outputs
1-3 = diff realizations of CCCma CGCM1 model
4 = ensemble mean of the 4 outputs with different
initial conditions done with same model
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Why do climate projections differ?
• Different resolution: 1.5 - 5° LL, 1° latitude ~ 100 km.
(affects ability to model small scale weather & climate
events, like thunderstorms)
• Different “sensitivities” (how much warming occurs for
given change in a radiative forcing, like a doubling of
CO2)
• Different parameterizations (estimations) of processes they
don’t have direct data for (e.g. clouds)
• Differences in what processes are coupled into model
(Oceans? Land use change?)
• Different emissions scenarios
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Greenhouse Gas Emission Scenarios
• A1 = techno-world: rapid economic growth & technogrowth, but remains heavily dependent on fossil fuels.
Different A1 scenarios are for diff techno
development
• A2 = business as usual
• B1 = Green global: economies shift towards less
materialism and techno-fix of more renewables.
Economies still run “globally” (as now)
• B2 = Green local: strong emphasis on local economies and
sustainable development, with moderate techno
and economic growth
Change in gas
concentration
under different
scenarios
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Ensemble of scenarios
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ensemble
temperature
projections
(all models
used, take the
mean)
Top fig: A2
bottom fig:
B2 scenarios
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Ensemble
precipitation
projections,
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A2 (be as
usual)
& B2 (green
local)
scenarios
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GCMs
• scales of 5°x5° Lat/long (500 km2) to 2.5°x2.5° (250
km2). Hadley is now going to 1.5° in new model
• theoretically can do 50km, but not practical
• many models, each good/bad at something
• “sensitivity” = how much warming does model give for
fixed forcing once reaches equilibrium (usu 2xCO2)
• w/o ocean, system stabilizes in 10s yrs
• w/ocean coupled, takes 1000s yrs
Differences among
models in projected
average global
temperature increase
for a given emission
scenario
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From IPCC 2001
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Level
Levelofofagreement
agreementamong
amongmodels
modelsfor projected temperatures
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Level of agreement among models for projected temperatures
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Level of agreement among models for
projections of precipitation
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Averages vs Individuality
• Problem - majority rules
• Can show each model, but still ask about level of
model agreement - so maj still rules
• Exceptions or extremes may be most likely
• Exceptions or extremes may be unlikely but high impact
(e.g. shutdown of N. Atlantic circulation)
• Solution - show ensembles, but also show extremes
Ocean currents also distribute heat around globe
Ocean Circulation Systems. Driven by winds, thermohaline circulation (salty cold water drops down, fresh
warm water floats up), and tides
Rahmstorf, S. 2002. Nature 419:207
Low probability, high impact extreme event:
The “Day After Tomorrow” scenario
Shutdown of North Atlantic Deep Water Circulation - figure shows changes in
surface air temperature if conveyor belt in Atlantic shuts down
Rahmstorf, S. 2002. Nature 419:207
Global temperature over the past 65 million
years.
6 5 million
years
10 million
PRESENT
55 million years
years
3.5 Million years
18,000 years
1 Million years
10,000 years
230,000 years
1,000 years
Impacts Resulting from Projected Changes in Extreme
Climate Events
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Projected Changes during the 21
Century in Extreme Climate
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Phenomena and their Likelihood
Simple Extremes
High er maximu m temperatures, more hot
days an d heat wavesd o ver nearly all land
areas (Very likely a)
Representative Examples of Projected Impacts
(all hig h confidence of occurrence in s ome areas
High er [In creas ing] minimum temp eratures ,
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fewer cold day s, frost day s and cold wav es
ov er n early all lan d areas (Very likely a)
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More in tens e precipitatio n even ts (Very
likelya, over many areas )
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Increased inciden ce of d eath and s erious illnes s in o lder ag e
gro ups an d urb an poor [4.7]
Increased h eat stress in liv es tock and wildlife [4.2 and 4.3]
Sh ift in tourist d es tinations [Table TS-2 an d 5.7]
Increased risk of d amag e to a number of crops [4.2]
Increased electric cooling d eman d and reduced en ergy su pply
reliability [Table TS-4 an d 4.5]
Decreased cold -related human morbidity and mortality [4.7]
Decreased risk of d amag e to a number of crops , and
in creas ed risk to others [4.2]
Extended range an d activ ity o f so me pest and dis ease
vecto rs [4.2 an d 4.3]
Reduced heating en ergy demand [4.5]
Increased flood, lands lide, avalan che, and mu dslide damage
[4.5]
Increased s oil ero sio n [5.2.4]
Increased flood runoff cou ld increas e recharg e o f so me
flo odplain aq uifers [4.1]
Increased p res sure on gov ernment and p rivate flood
in surance s ys tems and dis as ter relief [Table TS-4 and 4.6]
Impacts Resulting from Projected Changes in Extreme Climate Events
Complex Extremes
Increased summer drying over most midlatitude continental interiors and associated
risk of drought (Likely a)
Increase in tropical cyclone peak wind
intensities, mean and peak precipitation
intensities (Likely a, over some areas)e
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Intensified droughts and floods associated
with El Niño events in many different
regions (Likely a)
[See also under droughts and intense
precipitation events]
Increased Asian summer monsoon
precipitation variability ( Likely a)
Increased intensity of mid-latitude storms
(Little agreement between current models)d
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Decreased crop yields [4.2]
Increased damage to building foundations caused by ground
shrinkage [Table TS-4]
Decreased water resource quantity and quality [4.1 and 4.5]
Increased risk of forest fire [5.4.2]
Increased risks to human life, risk of infectious disease
epidemics and many other risks[4.7]
Increased coastal erosion and damage to coastal buildings
and infrastructure [4.5 and 7.2.4]
Increased damage to coastal ecosystems such as coral reefs
and mangroves [4.4]
Decreased agricultural and rangeland productivity in
drought- and flood-prone regions [4.3]
Decreased hydro-power potential in drought-prone regions
[5.1.1 and Figure TS-7]
Increase in flood and drought magnitude and damages in
temperate and tropical Asia [5.2.4]
Increased risks to human life and health [4.7]
Increased property and infrastructure losses [Table TS-4]
Increased damage to coastal ecosystems [4.4]