Global Warming:Talking with Skeptics

C. P. Leslie Grady Jr.R. A. Bowen Professor Emeritus

Environmental Engineering and Earth SciencesClemson University

Clemson, South Carolina

Many skeptics are at an early stage of the normal response to a life-altering event.

• Stages of grief (per Kubla-Ross)– Denial– Anger– Bargaining– Despair– Acceptance

• Recognition of climate change– Denial– Anger– Faith in technology– Minor changes in life-

style– Major changes in life-

style

Be aware that many skeptics are in the first two stages and respond appropriately to them.

It can be helpful to know in advance the assertions that skeptics may make.

• On November 12, 2007, Richard Black of BBC News published on BBC’s website the top 10 reasons why “climate skeptics” dispute the evidence that human activities are altering Earth’s climate1.

– Black compiled the reasons by e-mailing the 61 scientists from around the world who signed a letter in April 2006 to the Canadian Prime Minister expressing their doubts about climate change and the influence of humans.

– Black received advice on the list from S. Fred Singer, coauthor of Unstoppable Global Warming: Every 1500 Years, and a prominent skeptic about the role of humans in climate change and a signer of the letter.

• Black also presented counter-arguments made by scientists who agree with the assessment of the Intergovernmental Panel on Climate Change (IPCC).

– Black received advice on the counter-arguments from Gavin A. Schmidt, a climate modeler at the Goddard Institute for Space Studies and the Center for Climate Systems Research at Columbia University.

• The information to follow was based on Black’s report, but was augmented with information from my own reading and study.

1. “Climate scepticism: The Top 10” by Richard Black, BBC News, November 12, 2007. http://news.bbc.co.uk/2/hi/in_depth/629/629/7074601.stm

Skeptic Assertion 1: Evidence that Earth’s temperature is getting

warmer is unclear.

Counter-argument: A multitude of evidence tells us that global warming is occurring, including temperature

measurements and reconstructions, observations of glaciers and polar ice caps,

frequency of extreme weather, and changing ecosystems.

Skeptic Assertion 2: If the average temperature was rising, it has

now stopped. Observations from satellites and balloons show no warming compared to 1998.

• Variability from year to year is expected.

• 1998 was an exceptionally warm year because of a strong El Nino effect.

• Picking a specific warm year to start an analysis is “cherry-picking”.

Counter-argument:

Figure from http://www.globalwarmingart.com/wiki/Image:Satellite_Temperatures_png

Skeptic Assertion 3:Earth has been warmer in the recent past.

During the medieval warm period (950-1300), temperatures in Europe were warmer than today. The Arctic was warmer in the 1930s

than today.

Counter-argument: There have been many periods in Earth’s history that were warmer than today, but the causes don’t apply today.

Figure from http://www.clearlight.com/~mhieb/WVFossils/PageMill_Images/Temp_0-400k_yrs.gif

Caused by variations in:• Earth’s orbit around the sun (400,000 and 100,000 year cycles).• Changes in the tilt of Earth’s axis (~41,000 year cycle).• Precession of Earth’s axis (26,000 year cycle).• Changes in solar output.• Changes in Sun’s gravitational field.

Counter-argument: NOAA has stated that the idea that the medieval warm period was warmer than today has turned out to be incorrect.

Medieval WarmPeriod

Current temperatures in the Arctic are warmer than in the 1930s.Figure from Jansen, E., et al., 2007: Paleoclimate. In: Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Solomon, S., et al. (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.

Skeptic Assertion 4:Computer models are not reliable. They are

unable to model all of the processes influencing climate.

Counter-argument:• Climate is so complex that models are the only

way to see how the various factors interact.• Current models are highly sophisticated and

include land, ocean, sea ice, vegetation, and the atmosphere interacting in a fairly realistic way.

• All of the robust results from modeling have both theoretical and observational support.

Counter-argument (cont’d): Recent models can replicate 20th century climate.

• 58 simulations were performed with 14 different climate models. • Temperature anomalies are relative to the period 1901-1950. • Observed temperatures (black lines) are from the Hadley Centre/Climatic Research Unit gridded surface temperature dataset (HadCRUT3).

Figure from Hegerl, G.C., et al., 2007: Understanding and Attributing Climate Change. In: Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Solomon, S., et al. (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.

Skeptic Assertion 5:The atmosphere is not behaving as models predict.

Models predict that the troposphere should be warming faster than Earth’s surface. Measurements

show the opposite.

Counter-argument:Measurements show that the troposphere is warming as fast as or faster than Earth’s surface.

Figure from http://www.globalwarmingart.com/wiki/Image:Satellite_Temperatures_png

Skeptic Assertion 6:Climate is mainly influenced by the Sun. Earth’s climate has regularly responded to changes in the Sun’s energy output. Current warming can be attributed mainly to variations in the

Sun’s magnetic field and solar winds.

Counter-argument:• Solar variations do affect climate.• The difference between the solar minimum and

maximum over the 11 year solar cycle is one-tenth the effect of greenhouse gases.

• Instruments to study variations in the Sun’s magnetic field and solar winds have not been available long enough to establish trends with certainty.

• If variations in solar output are indeed contributing to warming, their effects will be amplified by elevated greenhouse gas levels.

Skeptic Assertion 7:Historical increases in carbon dioxide have lagged behind

temperature increases. They have not preceded them.

Counter-argument:• Indeed, ancient ice cores show CO2 lagging temperature

increases by about 700 years.• Historical temperature changes were caused by

variations in Earth’s orbit.• Today’s CO2 levels (35% increase over pre-industrial

levels) are higher than they have been in 650,000 years of ice core records, and possibly higher than at any time since 3,000,000 years ago.

• The energy imbalance caused by GHGs requires Earth’s temperature to increase even though orbital changes should be causing it to cool.

Skeptic Assertion 8: Satellite records are too short to justify claims that

hurricanes are becoming stronger or more frequent, or that there is anything exceptional about the apparent shrinkage

in Arctic ice.

Counter-argument:• Systematic collection of data in parts of the Arctic began

in the late 18th century.• Organized reconnaissance for Atlantic storms began in

1944.• Although these data are not from satellites, they are

sufficient to draw conclusions.• IPCC does not claim that global warming will make

hurricanes more frequent; only more intense.

Skeptic Assertion 9:Water vapor is the major greenhouse gas, accounting for

about 98% of all warming. Carbon dioxide and other GHGs have a relatively small impact.

Counter-argument:• The statement that water vapor is 98% of the

greenhouse effect is simply false. It contributes about 50%; clouds add another 25%; CO2 and other GHGs contribute the rest.

• Water vapor is essentially in balance with Earth’s temperature on annual time scales and longer.

• Other GHGs stay in the atmosphere on a time scale of decades to centuries, causing a lag in their effects.

• Water vapor concentrations increase in response to warming temperatures, causing a positive feedback effect, which is included in climate models.

Counter-argument (Cont’d) Simulations with mechanistic models establish the importance of CO2 and other anthropogenic GHGs on Earth’s temperature.

• Natural forcings include the effects of water vapor, solar variations, volcanoes, etc.• The yellow and light blue lines are the results from several models run under different conditions. The red and dark blue lines are averages.• Observed temperatures (black lines) are from the Hadley Centre/Climatic Research Unit gridded surface temperature dataset (HadCRUT3).

Figure from Hegerl, G.C., et al., 2007: Understanding and Attributing Climate Change. In: Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Solomon, S., et al. (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.

Skeptic Assertion 10:Problems such as HIV/AIDS and poverty are more pressing

than climate change. Governments and societies should respond proportionately, not pretend that climate change is

a special case.

Counter Argument:• Certainly problems such as HIV/AIDS and poverty require

our attention, as do many other problems associated with the developing world.

• The IPCC report shows that global warming will have disproportionately large effects on poor nations. Thus, it is imperative that we address it at the same time we are addressing other pressing issues.

• Developed nations caused the problem of global warming, so we bear a responsibility to solve it.

• Sharing our technology for alternative energy with developing nations will help them develop in a clean manner, a win-win solution for all.