Transcript Working Group I Contribution to the IPCC Fourth Assessment Report

Updates on the IPCC Fourth
Assessment Report (AR4)
Gerald A. Meehl
NCAR
Boulder, CO
The IPCC Fourth Assessment Report (AR4)
The Intergovernmental Panel on Climate Change
(IPCC) consists of about 190 governments that
commission assessments performed by the
international climate science community on the state
of human knowledge of climate and climate change
Working Group 1: Climate science
Working Group 2: Climate impacts and adaptation
Working Group 3: Mitigation
AR4 WG1 timetable
Apr 2003
1st Scoping meeting
Sep 2003
2nd Scoping meeting
Nov 2003
IPCC approval of outline
…….
Climate sensitivity workshop
(July, 2004, Paris)
Sep 2004
1st LA meeting
……
Zero order draft, internal review
All runs needed for WGI
May 2005
2nd LA meeting
Documentation needed (papers or
reports)
Aug 2005
1st draft, expert review
Dec 2005
3rd LA meeting
Mar 2006
2nd draft, Govt/expert review
Jun 2006
4th LA meeting
Sept 2006
3rd draft, review of SPM
Jan 2007
IPCC WG1 approval
All papers/documentation in press
or appeared
Working Group I Contribution to the IPCC Fourth Assessment Report
Climate Change 2007: The Physical Science Basis
Chapter 1: Historical Overview of Climate Change Science
Chapter 2: Changes in Atmospheric Constituents and in Radiative Forcing
Chapter 3: Observations: Surface and Atmospheric Climate Change
Chapter 4: Observations: Changes in Snow, Ice and Frozen Ground
Chapter 5: Observations: Oceanic Climate Change and Sea Level
Chapter 6: Paleoclimate
Chapter 7: Couplings Between Changes in the Climate System and Biogeochemistry
Chapter 8: Climate Models and their Evaluation
Chapter 9: Understanding and Attributing Climate Change
Chapter 10: Global Climate Projections
Chapter 11: Regional Climate Projections
22 CLAs, (7 Americans)
142 LAs, (27 Americans)
Climate models are a lot like weather forecast models, but
include interactive ocean, land surface, and sea ice components,
and also account for changes in atmospheric constituents like
greenhouse gases
Global mean surface temperatures have
increased
Latest view of last 2000 years of Northern Hemisphere
Temperature Change
Mann, M.E., Ammann, C.M., Bradley, R.S., Briffa, K.R., Crowley, T.J., Jones, P.D.,
Oppenheimer, M., Osborn, T.J., Overpeck, J.T., Rutherford, S., Trenberth, K.E., Wigley, T.M.L.
(EOS, 2003)
Latest view of last 2000 years of Northern Hemisphere
Temperature Change
Mann, M.E., Ammann, C.M., Bradley, R.S., Briffa, K.R., Crowley, T.J., Jones, P.D.,
Oppenheimer, M., Osborn, T.J., Overpeck, J.T., Rutherford, S., Trenberth, K.E., Wigley, T.M.L.
(EOS, 2003)
“Medieval
Warm
Period”
“Little Ice
Age”
“Global Warming” is real …
Land & Ocean
Ocean
Land
NOTE: warming
greatest over land
8 of top 10
warmest years
have occurred in
the last decade
Instrumental Observed Temperature Trends - ANNUAL
IPCC TAR (2001)
Natural forcings do not fully explain
observed late 20th century warming
• Climate models with
only “natural” forcings
(volcanic and solar) do
not reproduce observed
late 20th century
warming
• When increases in
anthropogenic
greenhouse gases and
sulfate aerosols are
included, models are
able reproduce
observed late 20th
century warming
“…most of the warming
observed over the last 50 years is
attributable to human activities”
---IPCC Third Assessment
Report, 2001
Climate change commitment:
at any point in time, we are
committed to additional
warming and sea level rise
from the radiative forcing
already in the system
(Meehl et al., 2005: How much more
warming and sea level rise? Science,
307, 1769—1772)
Surface temperature change in the 21st century from 21 models
early century
mid century
late century
Changes in hydrologic cycle by the end of the 21st century
temperature
precipitation
soil moisture
Precipitation intensity is projected to increase
particularly in the northern tier of states (warmer air
can hold more moisture, so that for a given event
more precipitation falls)
Dry days in between precipitation events increase
mostly in the southern tier of states, but in the Pacific
Northwest both precipitation intensity and dry days in
between events increase
Effects in Agricultural and Biological
Systems related to Frost Days—an example
from a climate model
Changes in frost days
affect:
Range shifts
(latitudinal or
altitudinal)
Change in growing
season length
Earlier flowering;
emergence of insects;
earlier mating; loss of
habitat, shorter
hibernation
Changes in frost days in the late 20th century show biggest decreases
over the western and southwestern U.S. in observations and the model
Future changes in frost days from the climate model
show greatest decreases in the western and
southwestern U.S., similar to late 20th century
Heat Waves
Have effects on
human mortality,
economic impacts,
ecosystem and
wildlife impacts
Climate models can be used to provide
information on changes in extreme
events such as heat waves
Heat wave severity defined as the mean
annual 3-day warmest nighttime minima
event
Observed
Model
Model compares favorably with presentday heat wave severity
In a future warmer climate, heat waves
become more severe in southern and
western North America, and in the
western European and Mediterranean
region
Meehl, G.A., and C. Tebaldi, 2004: More
intense, more frequent and longer lasting
heat waves in the 21st century. Science, 305,
994--997.
Future
Summary
Global warming is real, and most of the warming since the
late 20th century has been due to human activity
Cimate models can be used to reduce uncertainty by:
1. Quantifying the effects of forcing factors that influenced
climate during the 20th century (and over the past 1000 years)
2. Running multi-member ensembles to quantify the range
of model responses for future climate
3. Analysis of extreme events such as future changes in frost
days, heat waves and precipitation intensity shows how the
models can provide information on what changes could occur,
and why they could occur
Large-scale changes in atmospheric
circulation affect regional pattern of changes
in future frost days
Anomalous
ridge of high
pressure brings
warmer air to
northwestern
U.S.causing
relatively less
frost days
compared to the
northeastern
U.S. where an
anomalous
trough brings
colder air from
north
H
cold
L
warm
Climate model shows an
increase in the average
number of heat waves per
year in the future (top) and
an increase in heat wave
duration (bottom)
(model grid points near
Chicago and Paris)
The Chicago (1995)
and Paris (2003) heat
waves show large
positive 500 hPa
height anomalies
For present-day heat
waves near Chicago
and Paris, the climate
model also simulates
large positive 500 hpa
height anomalies
Atmospheric circulation
in heat waves becomes
more intense for future
climate (2080-2099)
compared to present-day
(1961-1990)
Future change in base
state (mean) atmospheric
circulation due to
increased CO2 is
conducive to more
intense heat waves
Kerr, R.A., Science 307 (11February 2005), adapted from K.R. Briffa and T.J. Osborn,
Science 295 (22 MARCH 2002), AND A. Moberg et al., Nature 322 (10 FEBRUARY
2005)