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Climate change: The latest science
David Karoly
School of Earth Sciences, University of Melbourne
TC Larry, 2006
From Bureau of Meteorology
• Different perspectives on climate change
• The latest assessment of climate change and its
causes - IPCC 2007
• Updates since 2007
• Climate change misinformation
• International agreements and stabilising climate
Global warming alarmism?
Garnaut Climate Change Review (2008)
• Climate change is a diabolical policy problem
• Australia has a larger interest in a strong mitigation
outcome than other developed countries
• We are already a hot and dry country;
small variations in climate are more damaging to
us than to other developed countries.
Senator Fielding’s views
• “The Rudd Government is yet to prove that man-made
carbon dioxide emissions are the main driver behind
climate change”
Intergovernmental Panel
on Climate Change (IPCC)
• Joint body of UN Environment Program and World
Meteorological Organization, established in 1988
• Every 5-6 years, carries out a comprehensive assessment of
climate change science, impacts, and approaches for
mitigation and adaptation to climate change
• Includes representatives from all countries
• Fourth Assessment Report prepared by more than 500
scientists over the last three years
• Summaries for Policy Makers approved by consensus
(including representatives of the Australian govt) at meetings
in Paris (Feb 07), Brussels (Apr 07) and Bangkok (May 07)
• Received the 2007 Nobel Peace Prize jointly with Al Gore
‘Warming of the climate
system is unequivocal,
as is now evident from
observations of
increases in global
average air and ocean
widespread melting of
snow and ice, and
rising global average
sea level.’ (IPCC 2007)
Figure SPM.3
‘Global atmospheric concentrations
of carbon dioxide, methane and
nitrous oxide have increased
markedly as a result of human
activities since 1750 and now far
exceed pre-industrial values
determined from ice cores spanning
many thousands of years.
The global increases
in carbon dioxide concentration are
due primarily to fossil fuel use and
land-use change, while those of
methane and nitrous oxide are
primarily due to agriculture.’
Figure SPM.1
Causes of climate change
In 2005, greenhouse gas concentration was 455 ppm CO2-eq.
A large part of the warming influence is masked by aerosols.
Climate modelling
• Physically-based tools for studying climate variability
and change
• Use mathematical representations of physical laws,
including Newton's second law of motion, the laws of
conservation of mass and energy, laws of
thermodynamics, and the ideal gas law
• Represent important processes in atmosphere,
ocean, land surface and ice, as well as coupling
between them
• More than twenty different models developed
independently around the world
Annual mean
Observations 1980-99
Multi-model ensemble
mean, 1980-99
WGI Fig 8.4
‘Most of the observed
increase in global average
temperatures since the mid20th century is very likely
(more than 90% certain)
due to the observed increase
in anthropogenic greenhouse
gas concentrations.’
WGI Fig TS.23
Figure TS.23
‘Continued greenhouse gas emissions at or above current rates
would cause further warming and induce many changes in the
global climate system during the 21st century that would very
likely be larger than those observed during the 20th century.’
‘There is now higher confidence in projected patterns of warming
and other regional-scale features, including changes in circulation
patterns, precipitation, and some aspects of extremes and of ice.’
• It is very likely that hot extremes, heat waves, and heavy
precipitation events will continue to become more frequent.
• Snow cover is projected to contract. Sea ice is projected to
shrink in both the Arctic and Antarctic.
• Storm tracks are projected to move poleward, with changes in
wind, precipitation, and temperature patterns.
• Increasing atmospheric CO2 concentrations lead to increasing
acidification of the ocean.
• 21st century anthropogenic CO2 emissions will contribute to
warming and sea level rise for more than a millennium, due to
the long timescales required for removal of this gas.
Projected climate
change hotspots
in Australia
(from IPCC AR4
WGII, chapt 11)
Observations to 2005
From Stroeve et
al, GRL, 2007
Sea ice in Sept 2007
From Stroeve et
al, GRL, 2007
Sept 2005
Observed and projected
Australian rainfall
Best estimate projected rainfall
change for 2070
(from “Climate change in Australia”)
Observed trend in
annual rainfall
Global CO2 emissions
from fuel consumption
Recent emissions
of IPCC emission scenarios and new growth path
CO2 Emissions (GtC y-1)
Actual emissions: CDIAC
Actual emissions: EIA
450ppm stabilisation
650ppm stabilisation
A1B: 2.42
A1FI: 2.71
A1T: 1.63
A2: 2.13
B1: 1.79
B2: 1.61
From Raupach et al. 2007, PNAS
SRES (2000)
growth rates in
% y -1 for 20002010:
Causes of climate change
Myth: The observed
warming has been due
to variations in solar
1. Increases in solar
irradiance would cause
warming in the upper
atmosphere and lower
atmosphere, but
cooling in the upper
atmosphere has been
From the Hadley Centre (UK)
Causes of climate change
Myth: The observed warming
has been due to variations in
solar forcing
2. Increases in solar irradiance
would cause more warming in
summer than winter, and in
daytime than nighttime, but the
opposite is observed
IPCC AR4 WGI Fig 3.2
Causes of climate change
Myth: The observed warming has been due to variations in solar
forcing associated with the solar sunspot cycle
Wrong! 1) Satellite observations show significant changes in
solar irradiance due to the 11-year sunspot cycle, but no long
term trend. However, global temperatures show a warming trend
but no 11-year cycle.
IPCC WGI Fig 2.16
Causes of climate change
Myth: Changes in cosmic rays have caused changes in
cloudiness, leading to global warming
No! Large 11-year cycle in cosmic ray activity, but no recent
No clear link between cosmic rays and clouds, as there are
plenty of CCN (cloud condensation nuclei) in many regions
Climate variations over the last millenium
Myth: The medieval warm period was warmer than present
Wrong! Multiple climate reconstructions show “the warmth of the
last half century is unusual in at least the previous 1300 years.”
Reconstructions of NH average temperature
WGI Fig TS.20
Recent observed global mean temperature
Myth: Global average temperature has cooled since 1998
Wrong! No significant warming or cooling, due to short period.
1998 the hottest year globally, due to El Niño event, and recent
cooling due to La Niña in 2007 and 2008. Rapid recent warming.
Long term warming, with the 2000’s the warmest decade
UN Framework Convention
on Climate Change (UNFCCC)
• Established following the United Nations conference on
Environment and Development in Rio de Janeiro in 1992
• Objective is “stabilization of greenhouse gas concentrations
in the atmosphere at a level that would prevent dangerous
anthropogenic interference with the climate system”
• “Such a level should be achieved within a time frame
sufficient to allow ecosystems to adapt naturally to climate
change, to ensure that food production is not threatened, and
to enable economic development to proceed in a sustainable
• Ratified by 192 countries, including USA and Australia,
and came into force in March 1994
Who has caused the problem?
UNFCCC includes principle that: “Parties should protect the
climate system...on the basis of equity and in accordance with
their common but differentiated responsibilities and respective
capabilities. Accordingly, the developed country Parties should
take the lead in combating climate change” (UNFCCC, Art.3.1).
Regional greenhouse gas emissions in 2004
SyR Fig 2.2a
Stabilisation scenarios
• 455 ppm CO2-eq in 2005, 379 ppm CO2 conc
• I: CO2-eq stabilisation at 445-490 ppm, emissions peak in 20002015, global CO2 emissions -85% to -50% in 2050, warming of
2.0 to 2.4C above pre-industrial
• Assuming equal per capita emissions, 50% global emission
reduction in 2050 means ~90% emission reduction for Australia
Probability distribution of committed global warming (relative to
preindustrial) for greenhouse gases in the atmosphere in 2005
From Ramanathan and Feng, PNAS, 2008
Key messages, Climate Change: Global Risks,
Challenges & Decisions, Copenhagen in March 2009
• Recent observations confirm that, given high rates of observed
emissions, the worst-case IPCC scenario trajectories (or even
worse) are being realized
• Recent observations show that societies are highly vulnerable
to even modest levels of climate change, with poor nations and
communities particularly at risk.
• Rapid, sustained, and effective mitigation based on coordinated
global and regional action is required to avoid "dangerous
climate change" regardless of how it is defined.
• Delay in initiating effective mitigation actions increases
significantly the long-term social and economic costs of both
adaptation and mitigation
• IPCC web site
• US GCRP “Climate literacy: The essential principles
of climate sciences”
• Climate change in Australia site
• Climate Works Australia FAQ on climate science
My contact information:
Prof David Karoly, School of Earth Sciences,
[email protected]