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Anthropogenic Climate Change:
What Science Tells Us About Global Warming
Dan Herms
Department of Entomology
The Ohio State University
Ohio Agricultural Research and Development Center
Wooster, OH
[email protected]
The 10 warmest years since 1000 AD:
1. 2010, 2005
Source: NASA Goddard
2. 2009
Institute for Space Studies
3. 1998
4. 2007
5. 2002
6. 2006
7. 2003
8. 2004
9. 2011 (warmest La Niña year on record)
10. 2001
Key questions to address:
1. Is global warming real and is it caused by
humans? scientific
2. If so, what will be the impacts? health,
agriculture, environment
3. What can be done: mitigation and / or
adaptation? policy: technological,
economic, cost / benefit
Key scientific questions:
1. Is Earth warming?
2. If so, what is the cause(s)?
3. What are / will be the impacts?
4. Future climate projections?
Consilience: convergence of evidence
4 independent surface temperature records:
NASA, NOAA, Hadley Climate Research Unit, Berkeley
Earth Surface Temp
Corroborated by:
• 2 satellite records of upper and lower troposphere
• Weather balloons
• Proxy reconstructions (e.g. tree rings, boreholes, ice cores,
glaciers, coral, etc.)
• Phenology, species distributions, physical evidence
4 independent surface temperature records
converge on the same pattern
Satellite and surface measurements agree:
Earth is warming
R.A. Rohde, www.globalwarmingart.com
Is the Earth warming? 30 year trends:
1. Increasing air temperature in lower atmosphere.
2. Increasing temperature over land.
3. Increasing temperature over oceans.
4. Increasing sea-surface temperature.
5. Increasing ocean heat content.
6. Increasing humidity.
7. Increasing sea level.
8. Decreasing glacier cover.
9. Decreasing sea ice cover.
10. Decreasing snow cover.
NOAA National Climatic Data Center, 2010
Record high temps far exceed record low temps
(if Earth was not warming the ratio would be 1:1)
Meehl et al. (2009) Relative increase of record high maximum temperatures
compared to record low minimum temperatures in the U.S., Geophys. Res.
Lett., 36, L23701, doi:10.1029/2009GL040736.
Warming did not stop in 1998
www.realclimate.org/wp-content/uploads/GISStrends.jpg
Earth has warmed almost 2ºF since 1860
compare to about 10°F difference between coolest
point of ice age and warmest inter-glacial maxima
At request of Congress in 2006, National Academy of
Sciences investigates and validates “hockey stick” surface
temperature reconstruction.
SURFACE TEMPERATURE RECONSTRUCTIONS FOR THE LAST
2,000 YEARS
NATIONAL RESEARCH COUNCIL OF THE NATIONAL ACADEMIES
THE NATIONAL ACADEMIES PRESS (2006)
www.nap.edu
Ocean temperatures show same pattern of warming
(source: NOAA)
http://www1.ncdc.noaa.gov/pub/data/oisst/ann.ocean.60s.60n.png
Climate Warming Inertia:
Most excess heat is trapped in the ocean where it will be
released slowly
Physical signs of warming are everywhere
Glaciers are melting world-wide
2000
Toboggan Glacier
Oerlemans, J. 2005. Extracting a climate signal from 169
glacier records. Science 308:675-677.
http://www.coasttocoastam.com/timages/page/glacier_bay012905.jpg
1909
Glacier Bay
Glacier National Park:
Number of glaciers in 1910 when park formed: 150
Number today: 25
http://www.globalwarmingart.com
The (Vanishing) Snows of Kilimanjaro
Unprecedented ice loss within
past 11,700 yrs:
85% of ice present in 1912 has
vanished.
26% of ice present in 2006 has
vanished.
www.commondreams.org/
Thompson et al. 2009. Glacier loss on Kilimanjaro
continues unabated. PNAS 106:19770-19775
The fabled Northwest Passage opened for first time
in 2007, and Northeast Passage opened in 2011
NASA, http://earthobservatory.nasa.gov
Trends in average Arctic sea ice since 1900
Steig et al. 2009. Warming of the Antarctic ice-sheet
surface since 1957. Nature 457:459-463.
http://www.nature.com/
Antarctic ice mass loss is accelerating:
2002-2005: 139 gigatons / yr
2006:
200 gigatons / yr
(contributing >0.5 mm to sea level rise)
Rignot et al. 2008. Nature Geoscience
Climate change at Thoreau’s Walden Pond
“We determined that plants bloomed seven days
earlier on average than they did in Thoreau’s times.”
Miller-Rushing & Primack. 2008. Global warming and flowering
times in Thoreau’s Concord: a community perspective. Ecology
89:332-341.
Climate change and phenology
at Sand County, WI
“The mean of regressions for the 55 phenophases
studied was -0.12 day / yr, an overall increase in
phenological earliness…”
Bradley et al. 1999. Phenological changes reflect climate change
in Wisconsin. Proc. Natl. Acad. Sci. 96:9701-9704
Change in growing season from satellite imagery
(days / decade)
Observation Geographic range
period
Earlier
leafout
Longer
growing
season
Reference
1981 – 1991
45 N 70 N, Eurasia
8
12
Myneni et al.
(1997a)
1981 – 1999
40 N 70 N, Eurasia
3.5
9.4
Zhou et al.
(2001)
1981 – 1999
40 N 70 N, North America
4.3
6.3
Zhou et al.
(2001)
1982 – 2001
25 W 60E; 27 N 72 N,
Europe
5.4
9.6
Stöckli &
Vidale (2004)
Badeck et al. 2004. Responses of spring phenology to climate change. New
Phytologist 162:295-309
New USDA Plant Hardiness Zone Map:
much of Ohio updated to warmer zone
PNAS (2006) 103:11217-11222
Bird phenology
Between 1971 and 1995 the laying date for many species
of British birds has shifted earlier by an average of 9 days.
(Nature 388: 526)
Breeding date of North American
common murre advanced by 24
days / decade
Toad phenology
Bufo bufo in southern England, 1980-2001.
Adult arrival at pond advanced by 11 d per 1°C
of warming.
Reading, C. J. 2003. The effects of variation in climatic temperature
(1980-2001) on breeding activity and tadpole stage duration in the
common toad, Bufo bufo. Sci. Tot. Environ. 310, 231-236.
OARDC is part of the National Phenology Network
that has documented earlier springs in NA
Lilac bloom as a phenological indicator
of continental-scale climate change.
Six undisputed facts:
1. The amount of heat trapped by CO 2 increases with
its concentration.
2. After remaining stable for thousands of years, CO 2
has risen rapidly to record levels, and is now rising
even faster.
3. After being relatively cool over the last millennium,
Earth has warmed sharply over the last 30 years.
4. Over 650,000 years, Earth’s temperature has been
tightly linked with atmospheric CO2.
5. Earth is absorbing more heat than it dissipates.
6. Ice is melting world-wide and sea level is rising.
Scientific “consensus” is based on a survey of
peer-reviewed literature, rather than polls of
opinions held by scientists.
1. Global warming is already apparent.
2. Anthropogenic greenhouse gasses are
responsible for the vast majority of the
warming.
Oreskes, N. 2004. The scientific consensus on
climate change. Science 306:1686
At request of President Bush, National Academy of
Sciences reviewed Third IPCC Report, and affirmed
its conclusions.
“Greenhouse gases are accumulating in Earth's atmosphere
as a result of human activities, causing surface air
temperatures and subsurface ocean temperatures to rise.”
National Academy of Sciences, National Research Council
2001 assessment of IPCC report:
http://www.nap.edu/openbook.php?record_id=10139
Official policy of Bush Administration as outlined by
Secretary of Energy Spencer Abraham:
• Global warming is real and caused, in part, by
humans.
• Stabilize greenhouse gasses at safe level.
• Reduce greenhouse gas intensity 18% by 2012 via
financial incentives and voluntary programs.
Abraham, S. 2004. The Bush Administration’s approach to
climate change. Science 305:616-618.
Earth’s energy balance:
•
•
•
•
Solar radiation emitted by Sun
Solar radiation intercepted by Earth
Energy radiated back to space
Energy absorbed, stored, redistributed as heat
Earth’s energy balance:
Kiehl, J. T. and Trenberth, K. E. 1997. Earth's annual global mean
energy budget. Bull. Am. Meteorol. Assoc. 78: 197-208.
Earth’s Energy Imbalance
Earth is absorbing 0.85 W / m2 more
than it is dissipating
Hansen et al. 2005. Science 308:1431-1435
Greenhouse effect keep Earth’s average
temperature (59°F) much warmer than the moon’s
(-1°F), and greatly dampen day-night temperature
fluctuations.
• Water vapor: 50% of greenhouse effect
• Clouds: 25%
• CO2: 19%
• Other (methane, ozone): 7%
Schmidt et al. 2010. The attribution of the present-day total
greenhouse effect. J. Geophys. Res. 115: D20106.
“CO2 and other noncondensing greenhouse gasses, which
account for 25% of the greenhouse effect, serve to provide
the stable temperature structure that sustains the current
levels of atmospheric water vapor and clouds via feedback
processes that account for 75% of the greenhouse effect.”
“Without the radiative forcing supplied by CO2 and other
noncondensing greenhouse gasses, the terrestrial
greenhouse would collapse, plunging the global climate
into an icebound Earth state.”
Lacis, et al. 2010. Atmospheric CO2: principal control knob governing
Earth’s temperature. Science 330:356-359.
Carbon emissions have increased exponentially
since dawn of industrial revolution…
http://upload.wikimedia.org/wikipedia/commons/5/56/Global_Carbon_Emission_by_Type.png
...increasing atmospheric CO2 from
280 ppm in 1800 to 386 ppm today
http://www.bom.gov.au/info/climate/change/gallery/images/25.jpg
Geological Carbon vs. Ecological Carbon
Geological carbon: as fossilized carbon that has been locked
in the Earth for millions of years (e.g. coal, oil) is extracted and
burned, concentration of atmospheric CO2 increases.
Ecological carbon: carbon that is continually recycled between
the atmosphere and living organisms (e.g. photosynthesis,
respiration, firewood, biofuels) remains in equilibrium and has
no effect on atmospheric CO2 concentration (exception: wide
scale deforestation).
http://www.apartmenttherapy.com
vs.
http://img.alibaba.com
http://www.globalwarmingart.com
Recent advances in paleoclimate:
Glaciers, bore holes, tree rings, stalactites,
coral, and fossils hold ancient records of:
• Temperature
• CO2
• Glacial cycles
• Solar radiation
• Volcanic activity
• Precipitation
• Wind and ocean currents
http://www.aad.gov.au/asset/images/525_ul-core.jpg
Leading to greatly increased understanding
of long- and short-term climate drivers:
•
•
•
•
•
•
Continental drift
Earth’s orbit / rotation
Solar radiation / sunspots
Volcanic activity
Greenhouse gasses
Air pollution
Earth’s temperature over 10 million years
http://www.bom.gov.au/info/climate/change/gallery/images/51.jpg
http://www.emporia.edu/earthsci/student/tinsley1/drilling.jpg
Nature 429, 623-628 (10 June 2004).
CO2 is at highest level in 650,000 years, and rising
R.A. Rhohde, www.globalwarmingart.com
Temperature and CO2 have been tightly linked
across eight ice ages
http://p6.hostingprod.com/@treks.org/arctic_800px-co2-temperature-plot.gif
Why do ice ages occur every 100,000 years?
http://members.aol.com/scipioiv/globice.jpg
Predictable variation in Earth’s orbit, wobble, and tilt
(Milankovic Cycles) change the amount of solar
radiation intercepted by Earth (solar forcing).
Eccentricity: 100K yrs
Obliquity: 41K years
Precession: 20K years
Milankovic Cycles generate ice ages every 100,000
years that last 80,000 years
http://math.ucr.edu/home/baez/Milankovitch_Variations.png
Bintanja and van de Wal. 2008. North American ice-sheet dynamics
and the onset of 100,000-year glacial cycles. Nature 454:869-872
Earth should now be cooling gradually…
http://images.allposters.com/images/102/039_ice_age_2sided.jpg
…and it was for 1000 years, until very recently.
http://math.ucr.edu/home/baez/temperature/1000.gif
But solar forcing due to Milankovic Cycles is not
strong enough to fully drive glacial cycles.
There must be feedbacks that amplify or dampen
solar forcing and accelerate climate change.
• CO2
• Water vapor
• Albedo (reflectance)
• Clouds
http://sitemaker.umich.edu/section2_group1/files/secondfeedback.jpg
Feedbacks as solar forcing warms Earth:
Decomposition releases greenhouse gasses: melting
permafrost releases huge amounts of CO2 and methane.
Oceans absorb less CO2: oceans saturate and more
CO2 remains in the atmosphere.
Humidity increases: water vapor is the most powerful
greenhouse gas.
Ice melts and white becomes dark: radiation that was
reflected to space is now absorbed as heat.
Positive Feedback: Temperature and CO2
http://p6.hostingprod.com/@treks.org/arctic_800px-co2-temperature-plot.gif
Feedbacks as solar forcing warms Earth:
Humidity increases: water vapor is the most powerful
greenhouse gas.
Decomposition releases greenhouse gasses: melting
permafrost releases huge amounts of CO2 and methane.
Oceans absorb less CO2: oceans saturate and more
CO2 remains in the atmosphere.
Ice melts and white becomes dark: radiation that was
reflected to space is now absorbed as heat.
Recent paradigm shift: paleoclimate
studies reveals sudden, not gradual,
climate change.
L.G. Thompson et al. 2006. Evidence of abrupt tropical
climate change: past and present. Proc. Natl. Acad.
Sci. USA 103:10536-10543.
Is there a “tipping point” beyond which
feedbacks generate unstoppable warming
even if CO2 emissions stabilize?
www.motherjones.com/
As the number of studies on climate have increased
exponentially, so has the level of understanding:
Temperature and sea level forecasts have been continually
revised upward.
Previous projections of increased warming (2-6 ºF) and
sea level rise (3 feet) by the end of this century are now
considered too conservative.
Global warming is altering ecosystems
Fish move north
http://news.nationalgeographic.com
Plant and animal life cycles
change
Corals bleach
Hoegh-Guldberg, O. 1999. Climate change, coral bleaching and the future
of the world's coral reefs. Marine and Freshwater Research 50:839–866.
“Global warming is the main cause of a significant
intensification in the North Atlantic Subtropical High (NASH)
that in recent decades has more than doubled the frequency of
abnormally wet or dry summer weather in the southeastern
United States.”
Li et al. (2011) J Climate 24:1499-1506.
Fire: more frequent and more intense
Since 2000: 6 worst wildfire years on record.
Since 2002: Acreage burned is 211% higher than 48
year average.
San Diego
Montana
John McColgan, BLM Alaska Fire Service
© 2004 San Diego State University Foundation
Westerling et al. 2006. Warming and earlier spring increase
western US forest wildfire activity. Science 313:940-943
The largest recorded bark beetle outbreak in human history in
northern British Columbia where winters used to be too cold for
the beetles to survive.
http://www.for.gov.bc.ca/hfp
Dezene Huber, UNBC
http://www.garna.org/
Kurz et al. 2008. Mountain pine beetle and carbon feedback to
climate change. Nature 452:987-990.
Sea level is rising:
20 cm in the last
century
R.A. Rhohde, www.globalwarmingart.com
Recent sea-level contributions of the Antarctic and
Greenland ice sheets. 2007. Science 315:15291532.
Antarctica 2002-2005:
Lost 31 cubic miles of ice.
Greenland 2003-2005:
Lost 27 cubic miles of ice.
Contribution to sea level rise: 0.35 mm / yr
NASA / German Aerospace Center Gravity Recovery and Climate
Experiment (GRACE)
Greenland ice mass losses
continue to accelerate.
ADAPTED FROM ISABELLA VELICOGNA,
GEOPHYSICAL RESEARCH LETTERS
Similar patterns in Antarctica are accelerating the rate of
sea level rise 5% per year.
Science (2009) 326:217
http://www.globalwarmingart.com
Extreme events:
Increased frequency of heavy precipitation
and heat waves.
Number of strong (class 4-5) hurricanes has
doubled.
Webster, et al. 2005. Changes in tropical cyclone number, duration,
and intensity in a warming environment. Science 309:1844-1846.
Hurricane Katrina was a Category 1 storm before
entering record warm Gulf waters
A Class 5 Hurricane
Long-term correlation between
cyclone frequency and tropical
Atlantic warmth.
Mann et al. (2009) Atlantic hurricanes
and climate over the past 1,500 years.
Nature 460:880-883.
NASA, http://visibleearth.nasa.gov/
Is the sun is responsible for recent warming?
There is no relationship between solar
activity and recent warming.
“Variations measured from satellites since 1978 are too
small to have contributed appreciably to accelerated
warming over the past 30 years.”
http://data.giss.nasa.gov/
Foukal et al. 2006. Variations in solar luminosity and
their effect on the Earth’s climate. Nature 443:161-166
Since satellite measurements began in 1979, no
relationship between solar irradiance and warming
http://www.realclimate.org/images//T_vs_solar.png
Since 1970, no relationship between solar activity and warming
Max Planck Institute for Solar System Research
www.mps.mpg.de/en/projekte/sun-climate/
No artifacts from urban heat islands
(urban and rural areas warming at same rate)
Peterson, TC. 2003. Assessment of urban versus surface temperatures
in the US: no difference found. J. of Climate 16: 2941-2959.
Alternative hypotheses considered and rejected
by IPCC and NAS:
• Earth’s orbit / rotation: slight cooling effect.
• Solar activity: atmosphere is warming from bottom
up, not top down.
• Ocean vents: ocean is warming from surface down,
not bottom up.
• Volcanic activity: Pinatubo eruption had short-term
cooling effect.
• Air pollution: global dimming caused by sulfate
aerosols has cooling effect (but is relaxing); however
black soot is having significant warming effect.
No volcanic signature on atmospheric
CO2 concentration
Internal climate variability: cooling effects of volcanic
eruptions and La Niña; warming effects of El Niño
http://data.giss.nasa.gov/gistemp/2011
Predicting future climate:
General Circulation
Models
www.usgcrp.gov
Compare to
reality
Develop
Model
Generate
predictions
Revise
model
Models accurately reconstruct past climate only when
they incorporate both natural and human influences
Modeled Global Mean Surface Temperature
natural forcing
human forcing
natural & human
http://www.grida.no/climate/ipcc_tar/wg1/007.htm#figspm4
Successful predictions of climate models
(observations predicted to occur by models before
the data were collected and/or inspected)
1. Surface warming but stratosphere cooling.
2. Energy imbalance between incoming sunlight and outgoing
infrared radiation.
3. Cooler nights after planes (and their contrails) were
grounded following 9/11.
4. Two years of global cooling caused by Pinatubo eruption.
5. Pattern of CO2 record in EPICA ice core (“The EPICA
Challenge”).
Climate sensitivity: amount of warming expected
with doubling of atmospheric CO2:
3°C with likely range of 2.0 – 4.5°C (3.6 – 8.1 °F)
Knutti, R. & G.C. Hegerl. 2008. The equilibrium sensitivity of the Earth’s
temperature to radiation changes. Nature Geoscience 1:735-743.
Climate models have underestimated recent increase
in rate of warming and sea level rise.
Rahmstorf et al. 2007. Recent climate observations compared to
projections. Science 316:709.
Largest uncertainty in models:
• climate feedbacks, especially clouds
• human behavior (how will CO2 emissions change?)
Patterns of Regional Warming in the US
NOAA National Climatic Data Center
Projected Climate Change Scenario for Ohio
Projected Impacts of Climate Change
Knuttie & Hegerl (2008) Nature Geoscience 1:735-743
Projected Impacts of Climate Change (IPCC TAR)
Business
as usual
Best case
scenario
http://www.globalwarmingart.com
Each “wedge” reduces CO2 emissions 1 billion tons over 50 yrs.
7 “wedges” to stabilize emissions: 525 ppm CO2, +5.4°F
(status quo = 850 ppm, +9°F)
•
•
•
•
•
•
•
•
•
•
•
•
•
Efficient vehicles: increase mpg from 30 to 60 (2 billion cars)
Drive less: from 10,000 to 5,000 miles / yr (for 30 mpg car)
Increase efficiency of buildings and appliances by 25%
Double efficiency of coal plants
Replace 1400 coal plants with natural gas (4X increase)
Capture CO2 at power plants (800 coal or 1600 gas)
Increase nuclear 2X to replace coal
Increase wind 50X to replace coal
Increase solar 700X to replace coal
Increase wind 100X to produce H2 for cars
Increase biofuels 150X (using 1/6 of Earth’s cropland)
Stop all deforestation, 2X tree planting
Conservation tillage on all crop land (10X current)
Pacala & Socolow. 2004. Stabilization wedges: solving the climate problem for
the next 50 years with current technologies. Science 305:968-972.
CO2 mitigation scenarios for next 50 years:
1. Maintain current rate of emissions increase: 800 ppm, +9°F
2.
•
•
•
•
•
Hold emissions at today’s rate: 525 ppm, +5.4°F
Double fuel economy; halve number of miles driven.
25% more efficient heating, cooling, lighting, appliances.
50% more efficient coal-fired plants.
Capture and store CO2 generated by power plants.
Replace 1400 coal plants with natural gas.
3. Reduce emissions by 50%: 450 ppm, +3.6°F
• All of the above but with complete elimination of coal.
• Increase nuclear 3X, biofuels 50X, solar 700X.
• Increase wind 50X to generate hydrogen for fuel-cell cars.
• Stop all deforestation.
Adapted from Pacala & Socolow. 2004. Science 305:968-972.
Since 2004, the number of wedges needed to
stabilize climate has increased from 7 to 9
R Socolow (2011) Wedges reaffirmed. Bull Atom Sci
http://www.thebulletin.org/web-edition/features/wedges-reaffirmed
Key scientific questions:
1. Is Earth warming? yes
2. If so, what is the cause? primarily,
anthropogenic greenhouse gasses
Inescapable conclusion:
Convergence of thousands of independent studies
from many disciplines provides overwhelming
evidence that:
• global warming is underway.
• it is caused by humans.
• future warming and sea level rise is inevitable.
Rejecting anthropogenic global warming
represents support for the hypothesis that CO2
can increase dramatically without warming
Earth, and that the ancient link between CO2
and temperature can somehow be uncoupled.
No evidence has emerged to
support this hypothesis.
Acknowledgements:
Dr. Lonnie Thompson, Byrd Polar Research Center,
The Ohio State University
Dr. Matt Ayres, Dartmouth College
Dr. Lyn Loveless, College of Wooster
Climate Science Websites
Intergovernmental Panel on Climate Change
www.ipcc.ch
US Global Change Research Program:
http://www.usgcrp.gov/usgcrp/
National Academy of Sciences Review of IPCC:
http://www.nap.edu/openbook.php?record_id=10139
Real Climate: climate science blog by climate scientists
www.realclimate.org
Ethical implications: statement of US Catholic Bishops
“Global Climate Change: A Plea for Dialogue, Prudence, and the Common Good”
http://www.usccb.org/sdwp/international/globalclimate.shtml