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Climate
Change:
The Scientific
Basis for
Concern
Physics Seminar
September 27, 2007
Lecture by G.A. McBean, Ph.D., FRSC
The global climate system
• Interacting
components:
atmosphere,
ocean, land
surface, sea ice,
glaciers…
• Processes are
complicated and
all components are
interconnected
Climate System and its Science
The system is complex and our understanding is
based on decades of scientific study
– Archimedes, Newton, …
– 1824 – Fourier – first paper on greenhouse
effect
– 1896 – Arrhenius- theoretical model of
Greenhouse
O3
Atmospheric RadiativeTransfer
Sun – 6000oK
Solar radiation
Earth – 288oK
Earth radiation
GREENHOUSE EFFECT –
gases in atmosphere trap energy and warm the surface and lower atmosphere
Warming:
Venus +500C
>90% CO2
90 atmos.
Earth +30C
5700 C
0.04% CO2
1% H2O
1 atmos.
Mars +10C
>80% CO2
0.007 atmos.
Carbon Dioxide
~25%
15 C
~10%
Other
~65%
Water Vapour
Climate System and its Science
The system is complex and our understanding is based on decades of
scientific study
– Archimedes, Newton, …
– 1824 – Fourier – first paper on greenhouse effect
– 1896 – Arrhenius- theoretical model of Greenhouse
– 1950’s
• International Geophysical Year - 1957
• Revelle – carbon cycle and oceans
• Phillips – atmospheric circulation models
– 1960’s
• Manabe – climate models
• 1967 – start of Global Atmospheric Research Program
• First weather satellites
– 1980 – start of World Climate Research Program
– 1986 – start of International Geosphere-Biosphere Program
– 1980’s – Vostok and other cores
The Earth’s climate has always been variable
Variation with Time
of the Vostok Isotope Temperature Record
4
Warm Periods
0
Variations in the Earth’s orbit around the Sun
and in the tilt of the Earth explain most of
these temperature variations
-2
-4
Temperature Variation (°C)
2
-6
-8
Ice Ages
400,000
400K years ago
300,000
“… global warming rates as
large as 2C per millennium…
-10
200,000
100,000
0
during retreat of glaciers
Years Before Present
NOW…”
US NAS report 2001
Source: Petit, et.al.
(PAGES / IGBP)
in the
Vostok Ice
2 Concentration
Carbon DioxideCOfrom
bubbles
trapped
inCore
Antarctic Ice
325
300 ppm
275
250
225
200
180 ppm
CO2 concentration (ppmv)
CO2 Concentration (ppmv)
300
175
150
400,000
400K years ago
300,000
200,000
Years Before Present
100,000
0
NOW
Source: Barnola, et.al. (PAGES / IGBP)
Temperature led but a reduced greenhouse
effect amplified the cooling
4
Vostok Ice Core CO2 Concentration and
Temperature Variation Record
300
2
275
0
250
-2
225
-4
200
-6
175
-8
150
- carbon dioxide
- temperature (polar)
180 to 310 ppm
-9 to +2 C
-10
300,000
0
- temperature
(global) 200,000 -5 to +1 100,000
C
NOW
Years Before Present
400K years ago
Ice age to
Present-like
400,000
Source: Barnola, et.al.; Petit et.al. (PAGES / IGBP)
Temperature Variation (°C)
CO2 Concentration (ppmv)
CO2 concentration (ppmv)
Temperature and
CO
3252 together.
Earth’s climate has varied considerably over its
billions of years history. Factors include:
- Sun and its changing intensity
-11 year solar cycle – 0.1% variation
-millions of years for larger, more gradual
change
- Variations in the Earth’s orbit around the Sun and the tilt
of the Earth’s axis of rotation
-20,000 yrs to 400,000 yrs
- Collisions with outside bodies - asteroids
- Changes in composition of the Earth’s atmosphere
-Volcanic eruptions – cool the planet
-Greenhouse effect – the topic of concern today
Climate System and its Science
The system is complex and our understanding is based on
decades of scientific study
– Archimedes, Newton, …
– 1824 – Fourier – first paper on greenhouse effect
– 1896 – Arrhenius- theoretical model of Greenhouse
– 1980 – start of World Climate Research Program
– 1986 – start of International Geosphere-Biosphere
Program
– 1980’s – Vostok and other cores
– 1988 – creation of Intergovernmental Panel for
Climate Change
Climate Science Assessment
• The Intergovernmental Panel on Climate
Change
– Established in 1988 by the World Meteorological
Organization and the United Nations Environmental
Programme
• Three Working Groups
– I. Science
– II. Impacts, Adaptation and Vulnerability
– III. Mitigation (Emission Reductions)
• Science Assessments – 1990, 1995, 2001, 2007
– Summaries for Policy Makers – www.ipcc.ch
IPCC Process
•
Preparation of draft Assessments
– lead and contributing authors - chosen on basis of their publications within
peer-reviewed scientific literature
•
Double peer-review process
– international community of experts (including those identified by
governments)
– experts and government representatives
•
•
•
2001 and 2007 assessments - more than 1000 scientific experts involved.
Focusing the science towards policy
Working Group I - The Science of Climate Change (800+ pages)
– responsibility of lead authors
•
Technical Summary of Working Group I Report (75 pages)
– accepted by the IPCC
•
Summary for Policy Makers (18 pages)
– Approved by Working Group I and accepted by IPCC
•
•
Similar process for WGs II and III
IPCC 2nd Assessment Synthesis of Scientific-Technical Information
Relevant to Interpreting Article 2 of the UNFCCC (17 pages)
– Approved by IPCC
Governments address climate (and ozone) issues
 1972 – Stockholm Conference on Environment
 1972 - Study of Man’s Impact on Climate
 1979 – First World Climate Conference - Geneva
 1980 – World Climate Research Program






1985 & 1987 – Villach, Austria Conferences
1985 – Vienna Ozone Convention
1985-6 – International ozone assessment
1985 – Antarctic ozone hole
1987 – Montreal Protocol of Ozone Convention
1988 - Toronto, Canada Conference [The Changing
Atmosphere: Implications for Global Security]
 1990 – London Protocol of ozone convention
 1988: Formation of the IPCC (by WMO &
UNEP)
 1990: 2nd World Climate Conference, Geneva
 1990: Intergovernmental Negotiating Committee for a
Framework Convention on Climate Change
Governments address climate (and ozone) issues
 1990 – First IPCC scientific assessment
 1992 – Rio – Earth Summit
 UN Framework Convention on Climate Change
 Conventions on biodiversity, desertification, …
 1994 – UNFCCC – ratified and in effect
 1995 – First Conference of Parties (Berlin)
 1995 – Second IPCC assessment
 1996 – Second Conference of Parties (Geneva)
 Science “good enough”
 1997 – Third Conference of Parties (Kyoto)
 Kyoto Protocol
 1998-2004 – CoP’s
 2001 – Third IPCC Assessment
 2004 – Kyoto ratified and in effect
 2005 – CoP11 – Montreal
 2006 – onward CoP’s
 2007 – 4th IPCC Assessment
Time scales of the greenhouse climate system
•
•
•
•
•
•
Recycle water in atmosphere
Mixing of greenhouse gases
50% of methane pulse to disappear
50% of CO2 pulse to disappear
Air temperature - response CO2 pulse
Sea level – response CO2 pulse
10 days
2-4 y
8-12y
50-200y
120-150 y
100’s y
Feedbacks
in Climate
System
Water
is an important
greenhouse gas,
but
-it re-adjusts quickly
Water
Water
More
water
-not
observed to be
changing very
much
CO2
More CO2
2
-itsCO
changes
areMore
a response
T=15
warming
CO2 emissions
More warming
evaporation
Water vapour feedback enhances warming
– positive feedback
High clouds
wetter
More CO2
warm
Clouds
More CO2
warm
warming
Low clouds
cooling
evaporation
Clouds can warm or cool
– positive or negative feedback
Feedbacks in Climate System
Water
CO2
T=15
Water
More CO2
warming
CO2 emissions
Less refection
of sunlight
More warming
Melt surface snow
Snow-albedo feedback enhances warming
– positive feedback
A reason for more warming in higher latitudes
Climate sensitivity
40% of warming due to direct greenhouse effect
60% due to feedbacks
Amplification - Water vapour = 1.6, Total = 2.5
Climate
Change:
The Scientific
Basis for
Concern
Is the climate changing?
Changing Greenhouse Gas Concentrations
from ice cores and modern data
Now
1957
Carbon dioxide
Last
10,000 y
Nitrous oxide
Methane
WGI The Physical Science Basis
Warming of the climate system is unequivocal,
as is now evident from observations of increases in global average air
and ocean temperatures, widespread melting of snow and ice, and rising
global average sea level.
Eleven of the last twelve years (1995 -2006) rank among the 12 warmest
years in the instrumental record of global surface temperature (since
1850).
The Last 50 Years
The Arctic is
warming most.
And
winters are
warming
more than
summers.
Climate
Change:
The Scientific
Basis for
Concern
Why is the climate changing?
Detection and attribution
How do we know the cause of change?
Construct climate models - based on our best understanding
of climate system
-Physics – motion, mass, energy, radiation
-Mathematics and computer science
-Chemistry
-Biology
And solve
on powerful
computers.
Compare observations with model simulations
Observations
Climate simulated by model
with volcanoes, solar variations and
other natural factors included.
Compare observations with model simulations
Observations Climate simulated by model
with greenhouse gases, aerosols,
“anthropogenic factors” included.
Compare observations with model simulations
Observations
Climate simulated by model
with natural and anthropogenic
all factors included.
Attribution
of Climate
Changein–global average temperatures
Most
of the observed
increase
there
a human
cause?is very likely due to the observed
sinceisthe
mid-20th
century
increase in anthropogenic greenhouse gas concentrations.
Greenhouse gases
CO2, Methane,…
Comparison of drivers
of change
Ozone
Land-use change
Aerosols
Jet contrails
Solar radiation
Solar forcing
vs
Total Human
forcing
Climate
Change:
The Scientific
Basis for
Concern
How will the climate change in the future?
Emissions scenarios – the global human choices
ΔCO2 = Δ (pop)*(Δ(GDP/pop)*Δ (energy/GDP)*Δ (CO2/energy)
(population)*(per capita wealth)*(energy intensity)*(carbon intensity)
CO2
CH4
N2O
SO2
Future climate change
“Our” impact
0.8? 3.4
2.8
warming °C per decade
1.8
0.18
0.13
0.2
Difference is 1 to 6oC – Ice Age
0.15?
Science
Uncertainty
And the warming
will continue for
centuries to follow
No one lives at the global average
Medium (A1B) scenario (2090-2099): Global mean warming 2.8oC;
Much of land area warms by ~3.5oC
Arctic warms by ~6oC.
Calculus of extremes
The distribution of weather events
around the climatic average follows a
‘bell-shaped’ curve.
A shift of 1 standard
deviation makes a
1 in 40 yr event into
a 1 in 6 yr event
Climate change can
involve change in the
average, or the spread
around the average
(standard deviation),
or both.
A shift in the distribution
of temperatures has a
much larger relative effect
Standard deviation
at the
than near
Most of
ourextremes
infrastructure
the mean.
1 in 40 yr high range
is designed for the
extremes of the past.
Need to look to future
and re-evaluate risk.
Projected changes with respect to standard
deviation of the parameter--sense of extremes
Heat Waves
More frequent hot days – virtually certain
Warm spells – very likely
Changing Precipitation and Water Supplies
Reduced wintertime
precipitation
Reduced summertime
precipitation
Projected changes with respect to standard
deviation of the parameter--sense of extremes
Heavy Precipitation Events
More heavy precipitation events – very likely
More drought areas – likely
85
The number of intense
cyclones is increasing
116
It is likely that future tropical cyclones will become
more intense, with larger peak wind speeds and more
heavy precipitation associated with ongoing
increases of tropical sea surface temperatures.
The tragedy of
The apparent increase in the proportion of very intense storms since 1970
Hurricane
Katrina
in some regions is much larger than simulated
by current models
for
that period.
Thermohaline Circulations - Conveyor
belt
• Deep circulations are due to density variations arising
from differences in temperature and/or salinity
(thermohaline)
• Move large amounts of heat poleward
Will this turn off
In the future?
Ahrens (1999)
Warming ofThe
between
1.7 and 2.7Cofleads
to
Probability
Large,
irreversible melting of the Greenland
Irreversible
Change
is Growing
ice sheet.
Global average
sea level will
increase
by 7m – few thousand years,
Double the rate of sea level rise in next century.
Joint science academies’ statement
Signed by the Presidents of academies of science
of all G8 countries plus those of China, India
and Brazil,
• “climate change is real”
• There must be actions to
• “reduce the causes of climate change”
• “prepare for the consequences of climate
change”.
Nations must work together:
• to reduce emissions - mitigation
• to adapt to a changing climate - adaptation.
An Open Letter to the Prime Minister of
Canada on Climate Change Science
• There is increasingly unambiguous evidence of changing climate in
Canada and around the world.
• There will be increasing impacts of climate change on Canada’s
natural ecosystems and on our socio-economic activities.
• Advances in climate science since the 2001 IPCC Assessment have
provided more evidence supporting the need for action and
development of a strategy for adaptation to projected changes.
• Canada needs a national climate change strategy with continued
investments in research to track the rate and nature of changes,
understand what is happening, to refine projections of changes
induced by anthropogenic release of greenhouse gases and to
analyse opportunities and threats presented by these changes.
• Signed by 90 Canadian climate science leaders from the academic,
public and private sectors across the country
• 18 April 2006
Climate
Change:
The Scientific
Basis for
Concern
Responding to climate change
3
4
2. Adaptation to
reduce impacts
and gain benefits
all the discussion by governments has been
ToAlmost
reduce
on how to reduce emissions.
Adaptation seems almost ignored as a public policy
Issue.
1
5
2
This is now changing in some provinces and institutions
1. Emission
reductions
Climate change
A simple framework
Changing
UN Framework Convention on
Climate Change
• signed by 155 nations in 1992 – came into force in 1994
• developed countries aim to reduce emissions to 1990
levels by year 2000
Article 2
“ … 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 food production is not
threatened and to enable economic development to
proceed in a sustainable manner.”
What is “dangerous”?
3oC
2o C
1oC
3.4
2.8
1.8
In this discussion – relative to pre-industrial T
prevent
dangerous anthropogenic interference
What is dangerous for Canada?
Canada’s Projected GHG Emissions
900
Business as Usual
Projections
Mt CO2 equivalent
850
800
+23%
750
700
2010 Emissions
809 Mt
? Mt
(1999)
699 Mt
1990 Emissions
607 Mt
240 Mt
650
600
550
36 Mt
Kyoto Target
571 Mt
6% below 1990
US +13%
500
1990
1995
23.5 G
2000
2005
26.4
2010
2015
2.5% of global emissions
2020
The Bottom Line
• The climate is changing –
• It will change more in the next 100 years
• Due to the long lifetime of greenhouse gases,
change is inevitable
• There is some challenging and exciting science
still to be done.
The End