"Natural and Human Causes of Climate Change: What Scientists Know and How They Know It" Presented by James M. Haynes, PhD, Interim Provost and Vice President for Academic Affairs, Professor of Environmental Science and Ecology For eons, six slowly, often intermittently acting natural forces have changed the Earth's temperature within a range of +7 degrees Fahrenheit, leading to climate swings from ice ages to planet-wide tropical conditions. Now, a seventh rapidly acting force is changing climate—modern human civilization. What evidences of climate change are observed today, and what is likely to happen to our children and generations beyond as a result of human activity in the recent past and today? What can we do to minimize the impacts of the changes to come?

1. Natural & Human Causes of
Climate Change: What Scientists
Know & How They Know It
James M. Haynes
Professor, Environmental Science & Ecology
Interim Provost & VP of Academic Affairs

2. GWCC
• Global Warming and Climate Change
–GW: a worldwide warming of the Earth’s
lower atmosphere
–CC: effects of GW on climate and, thus,
ecosystems = human life support systems
• A global issue with potentially huge
negative impacts on civilization and our
families for generations to come

3. Earth’s energy balance 
climate controlled naturally by…
• Orbital changes – Milankovich cycles
• Reflectivity of its surface – albedo
• Solar radiation input – sun cycles
• Solar radiation blocking – volcanic activity
• Ocean currents – global heat transfer
• Atmospheric gases – “greenhouse effect”

4. W. W. Norton
Fig. 18.39 a-cEccentricity
Tilt
Precession

5. Fig. 18.39 d
W. W. Norton

6. Albedo values
• Albedo = “whiteness” is
reflection of solar energy
by Earth (34% by atmosphere)
0.0 = 0% reflection of
light = black
1.0 = 100% reflection
of light = white
Albedo drops w/ >
water cover & >
particulates/aerosols
in atmosphere

7. Solar radiation: energy to Earth
fluctuates on many time scales
• >Sunspots  >Solar energy (18-23 year cycles)
• Also century, millennial & longer cycles

8. Volcanic activity cools the Earth
• Sulfur dioxide gas (SO2) & volcanic dust
ejected into atmosphere
–SO2 combines with water to form aerosol
mist of sulfuric acid (H2SO4)
• Geoengineering ideas

9. Ocean currents redistribute
heat on Earth’s surface

10. Greenhouse Effect: Fact of physics
known since 1860s
• For Earth to be in temperature equilibrium, VIS
+ UV energy from sun must equal infrared (IR)
energy radiated back into space
– Atmosphere transparent to UV + VIS but not IR
• Greenhouse gases in atmosphere absorb &
delay IR heat energy from leaving the Earth
– GHGs: CO2, CH4, N2O, CFCs, H2O vapor
– At 58o
F avg., Earth is ~50o
F warmer than w/o GHGs

12. CO2: Most important GHG - why?
• Most abundant and fastest changing GHG in
atmosphere with strong link to human activities
– Concentration in atmosphere : 280  >400 ppm in
past 150 years
• All anthropogenic: too fast for natural factors to
operate
– Highest volume GHG (water vapor): no change
– CFCs (let more UV in) and N2O & CH4 (let less IR out)
play relatively minor roles due to low amounts

13. Temperature-CO2 history of Earth
• Which is cause, which is effect? Last 50
years?
13

14. Biogeochemical cycle of carbon
14

15. Human disturbance of carbon cycle
• Note relative importance of human additions
vs. natural net fluxes
– 29 - 11 - 6 = 12 net GtC added to atmosphere yearly

16. Scientists are certain: global warming
is real and human-caused
• Melting Arctic, Greenland, Antarctic  sea level rise
10x faster than past 3,000 years  city/nation floods
• Glaciers retreating at the highest rates ever recorded
• Thawing permafrost in Northern Hemisphere
releasing huge amounts of CO2 & CH4
• Smoking gun: changing C13
/C12
ratio in atmosphere
consistent with burning ancient fossil fuels
– Atmosphere has a different ratio than living and fossilized
plants = coal, oil & natural gas
– Because photosynthesis favors C12
over C13
isotope

18. Climate deniers’ arguments &
scientists’ rebuttals (1)
• It’s just natural climate variability, right?
– “…just another warming episode, like the Mediaeval
Warm Period, the Holocene Climatic Optimum, or the
end of the Little Ice Age”
• Nope!
– Previous warming and cooling episodes were regional,
unipolar, and in a narrow range
– Current warming is global, bipolar, and over a wider
range than ever before

19. Climate deniers’ arguments &
scientists’ rebuttals (2a)
• “It’s just the sun, or cosmic rays, or volcanic activity
or methane (CH4)” — Nope, nope, nope & nope!
– No change in solar cycles in past 400 years
– No evidence of increase in cosmic radiation during the
past century
– Volcanoes erupt 0.3 Gt of CO2 per year, while humans
emit 29 Gt per year” = 10X volcanoes
– CH4 is a 21X more powerful greenhouse gas than CO2,
but there is 200 times more CO2 than CH4 in the
atmosphere = 10X warming impact by CO2 vs. CH4

20. Climate deniers’ arguments &
scientists’ rebuttals (2b)
Plot of solar energy input to the earth versus temperature of the last century. The two tend to track each
other until the last 30 years, at which time the earth warmed dramatically even as solar input went
down.

21. Strong scientific consensus
• Survey of all papers on climate change in Science from
1993-2003…
– 980 supported idea of human-caused global warming—none
opposed idea (peer review conspiracy?)
• 2009 survey of climate scientists familiar with the data…
– 97% agreed global warming is real & humans are the cause
• 2010 PNAS study
– 98% of scientists who study climate agreed that humans cause
global warming today
• Every major scientific organization in the world endorses
the idea of anthropogenic climate change
– Same level of confidence in gravity, relativity, evolution

22. Climate Models

23. IPCC: Intergovernmental Panel
on Climate Change
Forcing: a factor that drives
(‘forces’) the climate system to
change
Scientists use “proxies” to
determine change/time:
•Concentrations of isotopes 14
C
and 10
Be preserved in tree rings
and ice cores depend on solar
activity
•Volcanic eruptions preserved
as layers of dust/sulfate in ice
cores
•Concentration of CO2 & O2
isotope ratios in air bubbles
trapped in ice cores give data

25. So, if there’s no scientific debate…
• …why do people still deny climate change?
– Follow the money trail (fossil fuel companies and others that
benefit monetarily from status quo)
• “…offered $10,000…to scientists who would write negatively about
the IPCC [2007] report”
– Follow the political ideology trail: only solutions are more
government regulations & higher taxes (e.g., a carbon tax)
• Deniers followed lead of tobacco companies: “doubt is our product”
• “…generated an anti-science movement out of thin air and PR”
• Denier planning well-documented by responsible, not
fake, news media

26. “Reality must take precedence over public relations,
for Nature cannot be fooled” (R. Feynman)
• Conclusion: “there’s science, and…there’s the anti-science
of the global warming denial”
– “…nearly unanimous consensus among climate scientists that
anthropogenic global warming is real and that we must do
something about it” (analogy: cancer diagnosis)
– “…smokescreen, bluster and lies of the deniers has created
enough doubt that only half of the American public is
convinced the problem requires action”
– “U.S. is almost alone in…denial of this scientific reality”
• “…polls taken of 33,000 people in 33 nations in 2006 and 2007
show that 90% of their citizens regard climate change as a
serious problemand 80% realize that humans are the cause of it.”

27. Questions?