Source of much of the information and graphics for this presentation Intergovernmental Panel on Clim

1
Source of much of the information and graphics
for this presentationIntergovernmental 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

2
Research from the climate science community over
the past decade has strengthened the causal links
between observed changes in Earths 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.

3
Observed Changes in Earths climate
4

• 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
• Water vapor
• Carbon dioxide (industry, cars, wood fires)
• Nitrous oxide (fertilizing tilling land,
  industry, cars)
• Methane (wetlands, rice paddies, cows)
• Ozone (air pollution)

5
Indicators of the Human Influenceon the
Atmosphere during the Industrial Era
6
Global average temperatures are increasing with
increases in CO2.
7
The Relative Influences of Different forcing
Factors on Global Temperatures
8
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)
9
(No Transcript)
10
The relationship between temperature and carbon
dioxide over the past 160,000 years.
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
11
Climate Change AttributionHow 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

12
(No Transcript)
13
(No Transcript)
14
(No Transcript)
15
Percent of the Continental U.S. with A MuchAbove
Normal Proportion of Total Annual Precipitation
From 1-day Extreme Events(more than 2 inches or
50.8mm)
Source Karl, et.al. 1996.
16
Observed changes in Earths 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

• 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

17
Climate models
18
Global Climate Models

• Global Climate Model GCM
• Atmosphere-ocean general circulation models
  AOGCM (coupled ocean and atmosphere models)
• Regional Models - higher resolution than GCMs

19
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

20
1-3 diff realizations of CCCma CGCM1 model4
ensemble mean of the 4 outputs with different
initial conditions done with same model
21
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 dont have direct data for (e.g.
  clouds)
• Differences in what processes are coupled into
  model (Oceans? Land use change?)
• Different emissions scenarios

22
(No Transcript)
23
(No Transcript)
24
Greenhouse Gas Emission Scenarios

• A1 techno-world rapid economic growth
  techno- growth, 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

25
Change in gas concentration under different
scenarios
26
Ensemble of scenarios
27
ensemble temperature projections (all models
used, take the mean) Top fig A2 bottom fig B2
scenarios
28
Ensemble precipitation projections, A2 (be as
usual) B2 (green local) scenarios
29
GCMs

• scales of 5x5 Lat/long (500 km2) to 2.5x2.5
  (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

30
Differences among models in projected average
global temperature increase for a given emission
scenario From IPCC 2001
31
Level of agreement among models
Level of agreement among models for projected
temperatures
32
Level of agreement among models for projected
temperatures
33
Level of agreement among models for projections
of precipitation
34
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

35
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 419207
36
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 419207
37
(No Transcript)
38
Global temperature over the past 65 million years.
PRESENT
13 mya
1,000 ya
65 mya
39
Impacts Resulting from Projected Changes in
Extreme Climate Events
40
Impacts Resulting from Projected Changes in
Extreme Climate Events