IPCC and Climate Policy

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IPCC and Climate Policy

• Gerald A. Meehl
• National Center for Atmospheric Research
• Boulder, Colorado

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G8 Declaration on Fighting Climate Change, June
8, 2007 We take note of and are concerned about
the recent UN Intergovernmental Panel on Climate
Change (IPCC) reports.
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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
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AR4 WG1 timetable
All new model runs needed for WGI
Documentation needed (papers submitted to
journals) by May 31
All papers/documentation in press or appeared by
December 15
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Working Group I Contribution to the IPCC
Fourth Assessment Report
Climate Change 2007 The Physical Science
Basis Summary for Policymakers Technical
Summary 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
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Chapter 10 Global Climate Projections Coordinat
ing Lead Authors Gerald Meehl (USA), Thomas
Stocker (Switzerland) Lead Authors William
Collins (USA), Pierre Friedlingstein (France),
Amadou Thierno Gaye (Senegal), Jonathan Gregory
(United Kingdom), Akio Kitoh (Japan), Reto Knutti
(Switzerland), James Murphy (United Kingdom),
Akira Noda (Japan), Sarah Raper (Germany), Ian
Watterson (Australia), Andrew Weaver (Canada),
Zong-Ci Zhao (China) Review Editors Myles
Allen (United Kingdom), Govind Ballabh Pant
(India)
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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
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Ch. 10, Fig. 10.4, TS-32
(Anomalies relative to 1980-99)
Unprecedented coordinated climate change
experiments from 16 groups (11 countries) and 23
models collected at PCMDI (31 terabytes of model
data), openly available, accessed by over 1200
scientists over 200 papers Committed warming
averages 0.1C per decade for the first two
decades of the 21st century across all
scenarios, the average warming is 0.2C per
decade for that time period (recent observed
trend 0.2C per decade)
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Fig. SPM-5
(Differences relative to 1980-99)
Near term temperature projections are nearly
insensitive to choice of scenario or climate
model sensitivity and thus have a smaller
range Longer term temperature projections depend
on choice of scenario and various climate model
sensitivities, and thus have a larger range The
pattern of warming is similar for all time
periods regardless of scenario and similar to
those observed in the past 50 years
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Fig. SPM-6
Stippled areas are where more than 90 of the
models agree in the sign of the
change Precipitation increases very likely in
high latitudes Decreases likely in most
subtropical land regions This continues the
observed patterns in recent trends
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IPCC Plenary for acceptance of the AR4, Paris,
France, Jan. 29-Feb. 1, 2007
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Most of the observed increase in globally
averaged temperatures since the mid-20th century
is very likely due to the observed increase in
anthropogenic greenhouse gas concentrations---I
PCC Fourth Assessment Report, 2007
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IPCC AR4 press conference, Paris, February 2, 2007
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IPCC scientists in Washington, D.C., Feb. 8-9,
2007
Congressional Testimony before the House Science
Committee hearing before the Senate Environment
and Public Works Committee personal meeting with
Chairman Dingell of the House Energy and Commerce
Committee
briefing for House Energy and Commerce Committee
staff
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Full-page ad in New York Times, USA Today, and
others, February 14, 2007
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May 31, 2007 In recent years, science has
deepened our understanding of climate change and
opened new possibilities for confronting it. The
United States takes this issue seriouslySo my
proposal is this By the end of next year,
America and other nations will set a long-term
goal for reducing greenhouse gases. To help
develop this goal, the United States will convene
a series of meetings of nations that produce most
greenhouse gas emissions, including nations with
rapidly growing economies like India and China.

---George W. Bush
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G8 Declaration on Fighting Climate Change, June
8, 2007 We take note of and are concerned about
the recent UN Intergovernmental Panel on Climate
Change (IPCC) reports. The most recent report
concluded both, that global temperatures are
rising, that this is caused largely by human
activities and, in addition, that for increases
in global average temperature, there are
projected to be majorchanges in ecosystem
structure and function with predominantly
negative consequences for biodiversity and
ecosystems, e.g. water and food supply. We are
therefore committed to taking strong and early
action to tackle climate change in order to
stabilize greenhouse gas concentrations at a
level that would prevent dangerous anthropogenic
interference with the climate system. Taking into
account the scientific knowledge as represented
in the recent IPCC reports, global greenhouse gas
emissions must stop rising, followed by
substantial global emission reductions. In
setting global goal for emissions reductions in
the process we have agreed today involving all
major emitters, we will consider seriously the
decisions made by the European Union, Canada and
Japan which include at least a halving of global
emissions by 2050. We commit to achieving these
goals and invite the major emerging economies to
join usin this endeavour.
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October, 2007 IPCC and Al Gore awarded Nobel
Peace Prize
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November, 2007 Governor of state of Colorado
hosts reception at NCAR for Colorado IPCC
laureates
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June 7, 2008
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"I think we can actually get an agreement on
global climate change during my presidency. I
will just tell you that unless China and India
are at the table, unless they agree to a goal,
unless they agree to firm strategies to achieve
that goal, then I don't see how any international
agreement can be effective." --George W. Bush,
June 10, 2008
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Next Mitigation/adaptation (IPCC AR5 spring,
2013) New mitigation scenarios run with earth
system models will have implicit policy actions
to target future levels of climate change But we
can only mitigate part of the problem, and we
will have to adapt to the remaining climate
change The challenge use climate models to
quantify time-evolving regional climate changes
to which human societies will have to adapt
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• Summary
• The IPCC AR4 has had an unprecedented impact on
  public opinion and policy maker perceptions
• Now we are moving into the era of
  mitigation/adaptation scenarios that include
  policy actions
• The new challenge for the climate science
  community is to produce time-evolving predictions
  of regional climate change for adaptation and
  mitigation

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IPCC AR4 WG3
The higher the levels of stabilization, the
warmer the climate The longer we wait, the higher
the likely stabilization, and the warmer the
climate
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Projected Impacts of Climate Change
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Increased complexity ESMs and Impacts
Ice sheets
Schematic of an AOGCM (oval at upper left) and
Earth System Model (in orange oval) and various
types of impact models (right).
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• Coordinated climate change experiments
  (formulated by WGCM and AIMES) to be run for
  assessment in IPCC AR5
• Two classes of models to address two time frames
  and two sets of science questions
• Decadal prediction (2005-2030)
• higher resolution (50 km), no carbon cycle, some
  chemistry and aerosols, single scenario,
• science question e.g. regional extremes
• 2. Longer term (to 2100 and beyond)
• intermediate resolution (150 km), carbon cycle,
  specified/ simple chemistry and aerosols, new
  mitigation scenarios representative
  concentration pathways (RCPs)
  science question e.g. feedbacks

(Meehl and Hibbard, 2007 Hibbard et al., 2007)
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February 8, 2007 "The appropriate debate isn't
on whether climate is changing, but rather should
be on what we should be doing about it," Kenneth
Cohen, Exxon's vice president of public affairs,
told reporters on a conference call
Thursday. The call came less than a week after
an international panel of hundreds of scientists
said new research showed global warming was
"unequivocal" and that human activity was
primarily responsible for the most significant
factor in temperature change greenhouse
gases. "Climate is changing. It's a serious
issue. The evidence is there," Cohen said on the
call, which was arranged in part to allow Exxon
to state its position on the Intergovernmental
Panel on Climate Change's report.
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By the end of the 21st century, greater warming
occurs at high northern latitudes and over the
continents in the scenario simulations. We are
already committed to about another half a degree
of warming over North America by the year 2100.
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Global coupled climate models in 2006
Climate Models circa early 1990s
Global models in 5 yrs
Regional models
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Global and Regional Simulations of Snowpack
Regional Simulation
Global Simulation
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Temperature
Precipitation
Three 21st century scenarios
21 Models, Winter For Aspen
Early century
Mid-century
Late-century
- 0
- 0
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Temperature
Precipitation
A2 scenario by season
21 Models, four seasons, for Aspen
Early century
Mid century
Late century
- 0
- 0
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IPCC AR4 DJF surface_snow_area_fraction_where_lan
d 50 contour red 2080-2099, blue 1980-1999,
from 11 GCMs
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IPCC AR4 DJF surface_snow_depth (cm) 2080-2099
minus 1980-1999, from 10 GCMs shading anom gt 1
std. among 10 models
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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

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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)
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most of the warming observed over the last 50
years is attributable to human activities---IPC
C Third Assessment Report, 2001
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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. Warming stabilizes after several
decades, but sea level from thermal expansion
continues to rise for centuries. (Meehl et al.,
2005 How much more warming and sea level rise?
Science, 307, 17691772)
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We are already committed to about as much warming
as we experienced in the 20th century by the year
2100, but over three times as much sea level rise
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Global Warming and Aspen in the 21st century

• Gerald A. Meehl
• National Center for Atmospheric Research
• Boulder, Colorado

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Global Warming and Climate Models

• Gerald A. Meehl
• National Center for Atmospheric Research
• Boulder, Colorado

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• Summary
• Global warming is real, and most of the warming
  in the past several decades is due to human
  activity.
• Global climate models are used for climate change
  projections over large regions. Statistical
  downscaling techniques or regional models
  embedded in the global models are used to obtain
  climate change information for smaller regions
  (like the Aspen area).
• Climate change projections from the models
  indicate that Aspen will be warmer, with a
  shorter snow season especially at low elevations
  higher elevations are less affected. Changes in
  precipitation are dependent on model and season.

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Global Warming is real
Land Ocean
Ocean
8 of top 10 warmest years have occurred in the
last decade
Land
NOTE warming greatest over land
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Global mean temperatures are rising faster with
time
x
Period Rate Years ?/decade
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Upsala glacier in the Andes,
Argentina
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Warming of the climate system is
unequivocal---IPCC Fourth Assessment Report,
2007
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CCSM3 SUM(JAS) Sea Ice Concentration
(Teng et al., 2006, Cli. Dyn.)
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Changes in Arctic Sea Ice Cover
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Heat Waves Have effects on human mortality,
economic impacts, ecosystem and wildlife impacts
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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
Model compares favorably with present-day 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.
Observed
Model
Future
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