Download The Greenhouse Effect

The Greenhouse Effect
1. What is the greenhouse effect?
2. Are humans causing GHGs to rise?
3. Is the earth warming?
4. Are humans causing the earth to warm?
5. Have ecological effects occurred yet?
6. What about me?
1. WHAT IS THE GREENHOUSE EFFECT?
If the earth were the diameter of an apple, then the earth plus its
atmosphere would be the diameter of
a) A grapefruit
b) A basketball
c) An apple
The Atmosphere
• Nitrogen
• Oxygen
(N2)
(O2)
78%
21%
•
•
•
•
(CO2)
(CH4)
(O3)
(N2O)
.035%
0.00017%
0.000001%
0.000003%
Carbon dioxide
Methane
Ozone
Nitrous oxide
“Greenhouse” gases constitute a tiny portion of the atmosphere.
Gases that are triatomic or larger have greenhouse properties.
• Nitrogen
• Oxygen
(N2)
(O2)
78%
21%
•
•
•
•
(CO2)
(CH4)
(O3)
(N2O)
.035%
0.00017%
0.000001%
0.000003%
Carbon dioxide
Methane
Ozone
Nitrous oxide
From Philander, G. Is the Temperature Rising? Princeton Univ Press 1998
Greenhouse gases let heat in but not out.
UV radiated from sun
IR
refected
from
earth
Energy radiated from earth can be measured using satellites in space.
Greenhouse gases reduce the amount of energy escaping the atmosphere.
(Without the greenhouse
effect, life on earth as we know
it would not be possible.)
• The Greenhouse Effect is a factual physical
phenomenon.
• How to downplay it:
– Greenhouse gases (GHGs) are not rising
– GHGs rising, but the earth is not getting warmer
– Earth is warming, but
•
•
•
•
Humans didn’t do it
Feedback effects will save us
It is natural
Some scientists say we are OK
2. ARE HUMANS CAUSING ghgs TO RISE?
Climate Forcing – A change in energy flux between
earth and space.
– Positive forcing – warms earth
– Negative forcing – cools earth
Humans may affect climate forcing by putting
greenhouse gases into the atmosphere.
Humans have affected concentrations of greenhouse gases
Fossil fuel burning
Deforestation
Natural gas escape in extraction
Cattle belching
Rice cultivation
Landfills
Industrial fertilizers
Propellants
Refrigerants
Hansen, J. E., M. Sato, A. Lacis, R. Ruedy, I. Gegen, and E. Matthews, Climate forcings in the industrial era, Proceedings of the
National Academy of Sciences, 95: 12753-12758 (1998)
“Atmospheric CO2 (379 ppm) in 2005 exceeded by far
the natural range over the last 650,000 years.”
– Also true for methane (1,774 ppb)
IPCC 2007
Earliest fossils of Homo sapiens: ≈200,000 years
(IPCC—Intergovernmental Panel on Climate Change)
– Established by World Meteorological Organization & United
Nations Environment Program
– Scientists involved are generally primary researchers in climaterelevant fields
– Base assessments primarily on peer reviewed scientific
literature
– Release updated assessments every 6 years (1995, 2001, 2007)
Estimated changes in GHG forcings, 1850 – 2000
Hansen et al. (2000) PNAS 97:9875
(Concentration Change x Greenhouse Properties = Forcing Change)
GHG & temperature levels have fluctuated a lot over long time scales.
However, we are currently headed off the charts.
Brook, E. Nature 453:291
3. IS THE EARTH’S TEMPERATURE RISING?
“Warming of the climate system is unequivocal.” IPCC 2007
• Detection questions:
– Greenhouse gases are rising? (yes)
– The earth’s temperature is rising? (yes)
• Attribution question:
– Are anthropogenic ghgs causing the earth to warm?
4. ARE HUMANS CHANGING THE CLIMATE?
Reasons not to worry:
a.
b.
c.
d.
Net effects of humans are negative?
Warming is natural, not man-made?
Feedback effects will save us?
Some scientists say the evidence for anthropogenic
climate change is weak?
e. Things we can’t predict will make it better?
a. Anthropogenic Negative Forcings from Fossil
Fuels
Hansen et al. (2000) PNAS 97:9875-9880
However, net anthropogenic forcing is positive
IPCC 2007
b. Human v. Natural Warming: IPCC
1995: “The balance of evidence suggests a discernible human
influence on global climate.” (Civil, not criminal, standard of proof)
2001: “There is new & stronger evidence that most of the warming
observed over the last 50 years is attributable to human activities.”
2007: “Most of the observed increase in temperatures since the mid20th century is very likely due to anthropogenic greenhouse gas
concentrations.” (very likely = 90% certainty)
More time, better models, continued warming
c. Feedback effects – negative or positive?
– Some effects may dampen warming (negative)
• More warmth means more NPP
• More water in atmosphere: clouds shade planet
– Most feedback effects promote warming (positive)
• Permafrost melts: methane & CO2 released
• Loss of reflectivity from ice caps
• Biomass die-off due to rapid climate change
d. Some scientists say the evidence is weak
• Climate scientists compared for attitudes about
Anthropogenic Climate Change (ACC):
1. Convinced of ACC
• Scientists on the 4th IPCC
• Scientists who signed any of four statements endorsing the 4th IPCC
2. Unconvinced of ACC
• Signed any of 12 statements criticizing 4th IPCC
CE = convinced by evidence of ACC
UE = unconvinced by evidence
Timeline for Scientific Detection
= size of human signal
1995: “Balance
of evidence…”
2001: “New &
stronger evidence…”
2007: “Most…very
likely…”
Ability to solve the problem:
>
>
>
Size of human signal:
>
>
>
Conundrum Countdown -
e. Things we can’t predict will make it better unexpected effects
Heat storage by oceans: Climate change irreversible for
1000 years under 450 ppm scenario
• Solomon et al. (2009) PNAS 106:1704-1709
Skyrocketing CO2 emissions, better models: We may
need to reduce atmospheric CO2 below current levels
• Hansen et al. (2008) Open Atmos. Sci. J. 2: 217-231
“Because of the very long lifetime of CO2
emitted in burning fossil fuels, sky-rocketing
CO2 has brought us to an emergency situation
-- we need to cut off the CO2 source soon…I
had hoped that a CO2 amount as large as
about 450 ppm might be safe. It has become
very clear that was wrong -- the safe level is
no higher than 350 ppm, and it is probably
less than that…”
» J. Hansen, email to M. Orr, Feb. 3 2009
» Current CO2 is 380 ppm
Are Humans Changing the Climate?
Not to Worry Recap
a.
b.
c.
d.
e.
Net anthropogenic forcings positive
Feedback effects mostly positive
Human vs. natural warming mostly human
Scientist who say we’re okay are the minority
“Unexpected” effects making it worse
6. HAVE ECOLOGICAL EFFECTS BEEN
DOCUMENTED?
Some high elevation species at risk
Arenaria tetraquetr
(Europe)
The Pika (USA)
Krajick Science
303:1602 (2004)
Note different reflectance of different forest types
Beckage et al. 2008 PNAS 105(11):4197
159 species of
butterflies surveyed
every two weeks at 10
sites over 35 years
Avg. shift up = 95 m
Optimal elevation for 171 European plant species
Circles = 1905-1985
Triangles = 1985-2005
How far up has
distribution shifted?
Lenoir et al. Science 320:1768
Timing of flowering in Arctic plant species
Timing of an
event = phenology
Post et al.
Parmesan & Yohe Nature 421:37-42
A globally coherent fingerprint of climate change impacts across
natural systems
Trait
No. Species
No Change / No
Pattern
Warming -
Warming +
Phenology
677
27%
9%
62%
Distribution
893
27% / 24%
11%
39%
Phenology = timing of an event (e.g. flowering in the spring)
Climate + means it reproduces earlier (consistent with warming)
Climate - means it reproduces later (not consistent with warming)
Distribution = organisms’ geographic range
Climate + means it has shifted into historically colder habitat (e.g. upslope)
Climate - means it has shifted away from historically colder habitat
6. WHAT ABOUT ME?
H. sapiens on “Hedonic Treadmill” (Brickman & Campbell 1971)
Figure courtesy Chris Wolsko
7/9
7/9
Snowpack/precip = SWE/P
JFM Tmin = minimum temperatures
River flow
1/3
Stern Report: Economics of Climate Change
• Cost of stemming climate change: 1% GDP/yr
• Cost of doing nothing: 5% GDP/yr
• Cost of cutting 1 ton of CO2 emissions: $25
• 1 ton of CO2 has $85 in future costs
• Benefits of low-carbon future: $2.5 trillion/yr
See http://en.wikipedia.org/wiki/Stern_Review