Download Donner on climate science for CONS449C

Three most common questions
about climate change:
1. Is it real?
2. Is it caused by humans?
3. What should we do?
This is not
new science!
“On the influence of carbonic acid in
the air on the temperature of the
ground” - Svante Arrhenius, 1896
FINDING #1: The “Greenhouse effect”
96 % CO2
460 °C
~0.3% CO2
15 °C
FINDING #2: Greenhouse gas levels in the
atmosphere have increased
because of human activity
CO2 levels (ppmv):
End of ice age
Since the ice age
Mid-1800s
Mid-1800s
Mid-1950s
Mid-1950s
Today
Today
280
280
280
280
315
315
370
370
Source: NOAA ESRL
“Proof”: Decreasing fraction of
13C
in atmospheric CO2
Total emissions
Emissions
do not
necessarily
stay in the
atmosphere!
Atmospheric increase
Source: IPCC
Lesson #1
9 billion tons of carbon / year (FLOW or FLUX)
800 billion tons of carbon
(STOCK or POOL)
LAND
2
billion tons/yr
OCEANS
3
billion tons/yr
Today: 4 billion tons of carbon or 15 billion tons of CO2
are being added to the atmosphere each year
= almost 2 parts per million (ppm)
FINDING THREE: Temperature has increased
Why are
there so
many
datasets?
Observations of global rise in sea level
1.8 ± 0.5 mm per year since 1960
SHORTER LAKE
ICE “SEASON”
LESS SNOW COVER
BIRDS MIGRATING
EARLIER
OCEANS
WARMING
AND RISING
WARMER RIVERS
AND LAKES
CORALS
“BLEACHING”
PLANTS
FLOWERING
EARLIER
WARMWATER FISH
MOVING NORTH
PLANTS AND
ANIMALS MIGRATING
NORTH [AND HIGHER]
MORE FIRES
DISEASE AND
PEST OUTBREAKS
LESS ARCTIC ICE
THREE FINDINGS
Greenhouse gases warm the
Earth’s atmosphere
Greenhouse gas levels in the
atmosphere have increased
because of human activity
The climate has warmed
Attribution of climate change
We have done “detection”. Now the hypothesis is:
The global climate has warmed since the Industrial
Revolution due to the emission of greenhouse gases by
human activity.
H0: Not due to human activity (e.g. other factors at play)
Ha: Due to human activity
We need to do the math! What is the magnitude of the
enhanced greenhouse effect? What other factors have
influenced the climate since the Industrial Revolution
(e.g. the sun, internal variability)?
Probabilistic or Bayesian “truths”
We expect certainty from science
when it delivers probabilities
It is extremely unlikely (<5%) that the global pattern of warming
observed during the past half century can be explained without external
forcing.
It is very likely that anthropogenic greenhouse gas increases caused
most of the observed increase in global average temperatures since the
mid-20th century…
Are models the only “smoking gun”?
1. Warming in the
troposphere, cooling in the
stratosphere
2. More warming at night-time
3. Less radiation escaping to
space at wavelengths of
greenhouse gases
(Winters warming faster than summers, more
warming in the Northern Hemisphere, more
warming at high latitudes, etc.)
Temperature change by atmospheric layer
IPCC 2007
Warming faster at night
IPCC 2007
Absorption of outgoing longwave radiation
Starting in 1996, the Japanese
ADEOS satellite, recorded global
observations of the spectrum of
outgoing longwave radiation.
Some 27 years earlier, NASA had a
similar instrument on the Nimbus 4
spacecraft, between 1970 and 1971.
FINDING FOUR: The fingerprints
Multiple lines of evidence related to the
pattern of warming and the magnitude of
“natural forcings” suggests humans are the
primary cause
Neither the
future, nor
the past,
can be
known with
100%
certainty.
We must
evaluate
predictions,
whether
from models
or from
individuals,
probabilistic
ally.
Hypothesis testing
Question: Is the climate changing? (“detection”)
Hypothesis: The global climate has warmed since the
Industrial Revolution
Null hypothesis
H0: No trend in climate
Alternative hypothesis
Ha: Trend in climate
As opposed to weather (“what you get”), climate (“what
you expect”) is a statistical property. The answer to our
question requires an evaluation of whether the signal (the
trend) is statistically distinct from the noise.
A signal to noise problem
Global temperature anomaly (deg
C)
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
1980
1985
1990
1995
2000
2005
2010
Source:
A signal to noise problem
Global temperature anomaly (deg
C)
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
1980
1985
1990
1995
2000
2005
2010
Source:
A signal to noise problem
Global temperature anomaly (deg
C)
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
1980
1985
1990
1995
2000
2005
2010
Source:
A signal to noise problem
Global temperature anomaly (deg
C)
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
1980
1985
1990
1995
2000
2005
2010
Source:
Observed
global mean
temperature is
on the lower
end of the
range over the
past five
years.
Should models
be able to
simulate the
climate of a
particular
year, or
decade?
We ask every time
there’s a heat wave
or extreme event:
Is this [BLANK]
caused by global
warming?
Cover of Bloomberg Businessweek, owned by the Mayor of New
York City, after Hurricane Sandy struck New York
There are several ways, statistically-speaking, in
which the climate might change (in response to
some external or internal forcing – these examples
are not specifically about greenhouse gases!)
Source: IPCC
In these cases, a temperature extreme is more likely to occur
due to climate change. However, it could also have occurred
before the climate change.
So, a heat wave
may represent of
the type of
weather more
likely to occur due
to global warming,
but is not
necessarily caused
by global warming.
But what if the
event does not
have a precedent
(in the available
data***)?
March
2012
(NASA
data)
Probability and Climate Change
http://www.nasa.gov/topics/earth/features/warminglinks.html
Did Barry Bonds hit
home runs before he
took steroids?
Could Lance
Armstrong have one
the Tour de France
without doping?
UN Framework Convention on
Climate Change (Article II)
“The ultimate objective of this Convention and
any related legal instruments that the
Conference of the Parties may adopt is to
achieve”
“stabilization of greenhouse gas concentrations
in the atmosphere at a level that would prevent
dangerous anthropogenic interference with the
climate system.”
“350 (ppm) is the number that
leading scientists say is the safe
upper limit for carbon dioxide...
it's the number humanity needs to
get back to as soon as possible to
avoid runaway climate change.”
Source: IPCC, Hansen et al., 2008; 350.org
From Cancun Accord, signed at 17th COP to UNFCCC:
“… deep cuts in global greenhouse gas emissions are required
according to science… with a view to reducing global
greenhouse gas emissions so as to hold the increase in global
average temperature below 2°C above pre-industrial levels…
action to meet this long-term goal, consistent with science and
on the basis of equity… strengthening the long-term global
goal on the basis of the best available scientific knowledge,
including in relation to a global average temperature rise of
1.5°C”
Source: UNFCCC
“To protect at least 50% of the coral reef cells, global mean
temperature change would have to be limited to 1.2 C (1.1 –
1.4 C)”
Is this a scientific question?
Science can provide objective judgments based on
experimentation, evaluation of data and hypothesis testing.
The choice to take an action – whether set a pollution
standard or to determine an “acceptable” level of
greenhouse gases – is a normative judgment. It depends
on the values of the individual.
This judgment may take science into consideration, as well
as culture, economics, and the “zero-sum game” nature of
decision making.
“Pathways” to +2 deg C
Climate change: a “Super Wicked Problem”
“Super wicked problems” are wicked problems with
the following additional characteristics:
• Time available to solve the problem is running out.
• There is no central authority to impose a solution.
• Those in the best position to solve the problem are
also causing it
Lazarus, R.J. 2010. Super wicked problems and climate change:
restraining the present to liberate the future. Cornell Law Review
94: 1153-1234.