Transcript Climate Change: Science Issues

ECON*2100
Economic Growth and
Environmental Quality
Climate Change Lectures
I. Science Background
1
Slogans versus Evidence
• There is no area of public policy where the
reliance on dogmatic slogans instead of real
evidence has become so problematic
• The worst perpetrators are usually public
officials who are thought to have special
expertise or decision-making responsibility
2
Examples
• Gord Miller,
former Ontario
Environment
Commissioner
http://eco.on.ca/2014-ghg-looking-for-leadership/
3
Examples
• President Obama:
“[w]hat we do know is
the temperature around
the globe is increasing
faster than was
predicted even ten years
ago” (press conference,
November 14 2012,
reported in Washington
Post, 2012);
4
Examples
• Gina McCarthy,
US EPA
Administrator
5
Examples
• Gina McCarthy,
US EPA
Administrator
“climate change is driven, in large part, by carbon pollution, and it
leads to more extreme heat, cold, storms, fires and floods. For
farmers who are strained by the drought, for families with homes
in the path of a wildfire, for small businesses along our coastlines,
climate change is indeed very personal… Scientists are as sure
that humans are causing climate change as they are that cigarette
smoke causes lung cancer.”
6
So…
• Climate change is accelerating and is going
faster than model predictions
• Greenhouse gas emissions are clearly linked to
increasing trends in storms, droughts, extreme
weather, etc.
• But is any of this true?
7
IPCC (2013) on the slowing down of
global warming
• “Despite the robust multidecadal timescale
warming, there exists substantial multi-annual
variability in the rate of warming with several
periods exhibiting almost no linear trend
(including the warming hiatus since 1998).”
•
(IPCC, 2013: Chapter 2, page 39; emphasis added)
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IPCC (2013) on model over-estimation
• IPCC Ch. 9: 111 out of
114 models predicted
too much warming
since late 1990s
• Fyfe et al. (2013) GCM
trends averaged 0.21
oC/decade, more than
4x observed level
rossmckitrick.com
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IPCC (2012) on Extreme Weather
•
In the US “droughts have become less frequent, less
intense or shorter.”
•
Worldwide there is only “limited to medium” regional
evidence regarding changes in floods because the
records are sparse and the effects are confounded
with changes in land use and engineering.
“Furthermore there is low agreement in this evidence,
and thus overall low confidence at the global scale
regarding even the sign of these changes.”
“There is evidence that some extremes have changed
as a result of anthropogenic influences, including
increases in atmospheric concentrations of
greenhouse gases.” But “Attribution of single extreme
events to anthropogenic climate change is
challenging.”
•
•
10
So…
• Global warming is slowing down, not
accelerating
• Models over-predicted warming over past 2
decades
• Few identifiable trends in weather extremes
and little solid connection to GHG emissions
11
What do we mean by “global
warming”?
•
“Since the late 1960s, much of the North Atlantic Ocean has become less salty, in
part due to increases in fresh water runoff induced by global warming, scientists
say."
-Michael Schirber, LiveScience
June 29, 2005
•
“The surface waters of the North Atlantic are getting saltier, suggests a new study
of records spanning over 50 years. They found that during this time, the layer of
water that makes up the top 400 metres has gradually become saltier. The
seawater is probably becoming saltier due to global warming, Boyer says.“
-Catherine Brahic, New Scientist
August 23, 2007
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The Greenhouse Effect
• The sun sends energy to the Earth
• The Earth has to send it all back to space
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The Greenhouse Effect
• 2 ways energy leaves the Earth’s surface:
• Convection
• Radiation
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Convection
• Process that creates weather
• Warm, wet air rises
• Cool, dry air from above comes down
• Rain and wind cool the surface
15
Radiation
• The Earth is like a light bulb
• The light is too dim for our eyes to see
• “Infrared Radiation”
16
Different Proportions
• Stratosphere:
– Mostly radiation
• Surface & troposphere:
– Convection & radiation
17
The Greenhouse Effect
• The sun sends energy to the Earth
• The Earth has to send it all back to space
convection
radiation
18
The Greenhouse Effect
• Some gases absorb infrared light and warm up
–
–
–
–
Water Vapour
Carbon dioxide (CO2)
Methane
A few others
• Water Vapour does 95% of the absorption
19
What happens when we burn fossil
fuels?
• The amount of CO2 in the air
is going up a little each year
20
The Greenhouse Effect
• The sun sends energy to the Earth
• The Earth has to send it all back to space
convection
radiation
• Now some more of the infrared energy is absorbed
21
The problem…
• While the radiative changes are relatively
straightforward to model (linear)…
• Convection, or fluid dynamics, are very difficult
to model (highly nonlinear)
• Consequently the problem can only be
analyzed using empirical approximations
22
What do people agree on?
• CO2 is a greenhouse gas (infrared absorbing)
• CO2 concentration in the atmosphere is going up due to
fossil fuel use
• All other things being, this is likely to cause an increase in
temperatures
• Since the early 1800s, the world has warmed
• Changes due to CO2 are relatively small: large changes
require large feedback processes to kick in
23
Where are the disagreements?
• Feedbacks and amplification mechanisms
– Models versus observations
• Whether natural variability explains some or
most of modern climate changes
• Whether the changes are harmful or not
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97% Consensus?
• Obama 2013: “97% of scientists agree climate change is
real, manmade and dangerous”
– Survey questions: Is CO2 a greenhouse gas, and do human
activities contribute to climate change?
– 77 out of 79 agreed
– “97% of scientific papers say…” In fact the majority (66%) took
no position, 33% accept at least a weak role for GHG’s
– 2012 American Meteorological Society survey: only 52% agreed
humans responsible for most recent global warming
25
Long Term Context
• The climate varies
naturally on long
and short time
scales
Long Term Context
• CO2 levels vary too
Modern Warming in Context
• Ice core record 420,000 years
28
The world’s longest thermometer record –
Central England – 1650 to 2013
29
Modern warming: pattern
• Surface air temperature averages are typically
used
• Also tropospheric air temperature, sea ice,
etc.
• Major regions:
– Land
– Ocean
– Northern Hemisphere
– Southern Hemisphere
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Land record sample size
• Collapsing sample size
31
Land record sample size
• Growing bias towards airports
32
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34
35
ross.mckitrick.googlepages.com
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ross.mckitrick.googlepages.com
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Land and Ocean
Land
Ocean
39
NH and SH Sea Ice 1979 – 2013
40
Is there a problem?
• [Present] emission trends put the
world plausibly on a path toward 4°C
warming within this century. Levels
greater than 4°C warming could be
possible… Current scientific evidence
suggests that even with the current
commitments and pledges fully
implemented, there is roughly a 20
percent likelihood of exceeding 4°C by
2100, and a 10 percent chance of 4°C
being exceeded as early as the 2070s.
– Potsdam Institute for Climate Studies
41
Is there a problem?
• The only sure thing is what we have so
far been able to measure…The warming
we have had over the last a 100 years is
so small that if we didn’t have had
meteorologists and climatologists to
measure it we wouldn’t have noticed it
at all… It indicates that the climate
sensitivity is probably lower than climate
models, at least initially adopted.
– Lennart Bengtsson, European Weather
Centre, Head of Atmospheric and Space
Science Institute, Bern
42
Is there a problem?
• Warming of the climate system is
unequivocal, and since the 1950s, many of
the observed changes are unprecedented
over decades to millennia…Human
influence on the climate system is clear.
This is evident from the increasing
greenhouse gas concentrations in the
atmosphere, positive radiative forcing,
observed warming, and understanding of
the climate system…It is extremely likely
that human influence has been the
dominant cause of the observed warming
since the mid-20th century.
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Is there a problem?
• The IPCC iconic statement that there is a
high degree of certainty that most of the
warming of the past 50 years is due to
man’s emissions is, whether true or not,
completely consistent with there being no
problem. To say that most of a small
change is due to man is hardly an
argument for the likelihood of large
changes.
– Richard Lindzen, Meteorologist, MIT
44
Amplification mechanisms
• Water vapour feedback
– As air warms it can hold more moisture
– Add a little CO2
– Air warms a little
– H2O level rises
– Air warms a lot
45
Amplification mechanisms
• Ice-albedo feedback
– “albedo” = reflectivity of surface
– Snow-covered ice is highly reflective
– Ocean surface is much less so
– If polar regions warm, sea ice retreats a bit
– Oceans then absorb more solar energy, warming
more
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Feedbacks
• Without feedbacks, doubling CO2 would warm
up surface in a simple climate model by about
1C
47
Feedbacks
• IPCC projects CO2 doubling (going from 280 ppm
to 560 ppm) will cause 1.5 – 4.5 C warming
• In other words, feedbacks are strongly positive
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Feedbacks
• The scientific problem:
– Feedbacks cannot be resolved from basic physics
or first principles
– They have to be simulated in numerical models
then tested empirically
– Small uncertainties in feedbacks translate into
large uncertainties in forecasts
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Testing Feedbacks
• Tropical Troposphere
• Equilibrium Climate Sensitivity
50
Tropical Troposphere
Most rapid warming is expected
to occur in 2 regions:
- tropical troposphere
- polar surfaces
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Tropical Troposphere
•
•
•
•
•
Half the planetary atmosphere
Most incoming solar energy enters climate there
High humidity = abundant water vapour
55% of amplification effect occurs here in models
Temp’s monitored by weather balloons since 1958, satellites since 1979
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Tropical Troposphere
• The problem: Not much warming there
despite CO2 levels going up 18% since 1979
Current Model
Spread
Current
Observations
53
Tropical Troposphere
• Since 1958, CO2 up by
30%
• Except for step change in
1978, no trend in midtroposphere; almost no
change in lower
troposphere
• Models predict far too
much warming
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Tropical Troposphere
• Models
• Balloons
Satellites
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ECS
• Equilibrium Climate Sensitivity
• Amount of warming in a model after
instantaneously doubling CO2 level, and then
allowing all processes to come to equilibrium
• Traditional range: 1.5 – 4.5 deg C
• But models can show much higher top end
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ECS
• Using simplified models the distribution is
very wide
•
Roe & Baker, Science 2007
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ECS
• But recent empirical studies have yielded estimates at or near the bottom
end:
– Lewis, N. (2013): ECS best estimate 1.64 °𝐂, likely range 1.3 – 2.2 °C
– Lewis, N. and Curry, J. (2014) ECS best estimate 1.64 °C, likely range 1.1 –
4.1°C
– Aldrin, M. et al (2012): ECS best estimate 1.76 °𝐂, likely range 1.3 – 2.5 °C
– Ring, M.J. et al. (2012): ECS best estimate 1.80 °𝐂, likely range 1.4 – 2.0 °C.
(Note ECS falls to 1.6 °𝐂 if HadCRUT3 temperature data is replaced by
HadCRUT4.)
– Otto, A., et al., (2013): ECS best estimate 1.91 °C, likely range 1.3 – 3.0 °C
– Masters, T. (2013): ECS best estimate 1.98 °𝐂, likely range 1.2 – 5.2 °C
– Loehle, C. (2-14): ECS best estimate 1.99 °𝐂, likely range 1.7 – 2.2 °C
– Johanssen et al. (2015): ECS best estimate 2.50 °𝐂, likely range 2.0 – 3.2 °C
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ECS
• But recent empirical studies have yielded estimates at or near the bottom
end:
– Lewis, N. (2013): ECS best estimate 1.64 °𝐂, likely range 1.3 – 2.2 °C
– Lewis, N. and Curry, J. (2014) ECS best estimate 1.64 °C, likely range 1.1 –
4.1°C
– Aldrin, M. et al (2012): ECS best estimate 1.76 °𝐂, likely range 1.3 – 2.5 °C
– Ring, M.J. et al. (2012): ECS best estimate 1.80 °𝐂, likely range 1.4 – 2.0 °C.
(Note ECS falls to 1.6 °𝐂 if HadCRUT3 temperature data is replaced by
HadCRUT4.)
– Otto, A., et al., (2013): ECS best estimate 1.91 °C, likely range 1.3 – 3.0 °C
– Masters, T. (2013): ECS best estimate 1.98 °𝐂, likely range 1.2 – 5.2 °C
– Loehle, C. (2-14): ECS best estimate 1.99 °𝐂, likely range 1.7 – 2.2 °C
– Johanssen et al. (2015): ECS best estimate 2.50 °𝐂, likely range 2.0 – 3.2 °C
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Model-Observation Discrepancy
IPCC AR5 report
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Model-Observation Discrepancy
• IPCC AR5, Box 9.2 Figure 1
• Note middle panel begins with volcano and ends with an
El Nino
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Model-Observation Discrepancy
• ‘The growing divergence
between climate model
simulations and observations
raises the prospect that
climate models are inadequate
in fundamental ways,’
– Judith Curry, Climatologist, Chair
of Earth and Atmospheric
Sciences, Georgia Tech
62
Model-Observation Discrepancy
• “If things continue as they have
been, in five years, at the latest, we
will need to acknowledge that
something is fundamentally wrong
with our climate models…A 20-year
pause in global warming does not
occur in a single modeled scenario.
But even today, we are finding it
very difficult to reconcile actual
temperature trends with our
expectations.”
– Hans von Storch, Climatologist , GKSS,
Germany (2013)
63
Conclusions
• The basic points on which there is wide scientific
agreement establish that humans can, and likely do,
influence the climate system by raising the
atmospheric CO2 fraction
• On its own this is not enough to prove that the changes
pose a problem, or even will be large enough to notice
• Making that argument requires additional assumptions
about positive (amplifying) feedbacks, as represented
in computer models of the climate system
64
Conclusions
• A lot of credible scientists working on the
problem believe the positive feedbacks are large
enough to pose problems in the years ahead
• But key discrepancies between models and
observations are raising the likelihood that
models overstate the feedbacks and the
sensitivity of the climate system to CO2 emissions
• The next 4-5 years will likely suffice to settle this
debate
65
Conclusions
• Science is always about the weight of the
evidence. Few things are provable in an
absolute sense. One must always be open to
surprises, reinterpretations, and the possibility
that one has been wrong …
• Climate change presents us with one of the
most difficult of all scientific problems, heavily
encumbered with the need to make political
and economic decisions long before hard
evidence is at hand.
– Carl Wunsch, Professor of Physical Oceanography,
MIT
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