Invited Post by John Nail, Ph.D.
We need to first start with some definitions, as people often confuse the following.
The Greenhouse Effect is a well-established physical effect. Technically, the Greenhouse Effect is the absorption (and eventually conversion to heat) of infrared (IR) radiation by an atmospheric gas. Nobody with any scientific credibility denies the Greenhouse Effect.
Global Warming refers to any long-term increase in average Earth temperature. When discussing any possible Global Warming, we must distinguish between weather and climate.
Weather refers to the conditions (air temperature, atmospheric humidity, atmospheric pressure, wind direction and speed) present at a particular time.
Climate refers to long-term general weather conditions. Climate refers to several years, if not decades. Low air temperatures in January and high air temperatures in August are examples of weather. Years of low (or high) rainfall per year are examples of climate. Global warming is an example of a possible climate (long-term) change; people often confuse it with weather (day to day) changes.
Climate Change is a broad category that incorporates Global Warming and any other possible changes, such as long-term changes in precipitation, the frequency of severe weather events (tornados, hurricanes, blizzards, etc.). Global Warming is a subset of Climate Change.
As mentioned above, we know that the Greenhouse Effect is a well-established scientific knowledge; it is a fact that a Greenhouse Effect operates on Earth. Earth’s average surface temperature is generally accepted to be somewhere close to 59o F (15o C). If there was not a Greenhouse Effect on Earth, it is believed that average Earth surface temperature would be somewhere close to 0o C (- 18o C).
The Enhanced Greenhouse Hypothesis:
Premise 1) Fossil fuels produce carbon dioxide (CO2) when they are used.
Premise 2) Carbon dioxide is a Greenhouse Gas (GHG).
Premise 3) Greenhouse Gases increase atmospheric temperature.
Conclusion: The atmospheric carbon dioxide from our use of fossil fuels would expected to be causing an increase in average global Earth temperature, also known as Global Warming.
The Enhanced Greenhouse Hypothesis is relatively simple and logical. The problem is that the reality is much more complex.
Question 1: Is carbon dioxide the only greenhouse gas?
Answer: No. Methane, nitrous oxide, and water vapor are other greenhouse gases.
Question 2: How much of the greenhouse effect is due to carbon dioxide?
Answer: Carbon dioxide has been estimated to produce 26% of the Greenhouse Effect during clear skies (source: Kiehl and Trenberth, Earth’s Annual Energy Budget, Bulletin of the American Meterological Society volume 78, issue 2 (1997), pages 197-208).
Question 3: Which greenhouse gas is the largest contributor to the Greenhouse Effect?
Answer: In clear skies, water vapor produces 60% of the Greenhouse Effect (source: see above).
Question 4: Why do the answers to Questions 2 and 3 specify clear skies?
Answer: Clouds complicate the Greenhouse Effect. During the day, clouds reflect sunlight from Earth atmosphere back into space. Anyone who has ever seen a planet (Venus, Mars, etc.) in the night sky has seen sunlight that was reflected back into space by either clouds in the planet’s atmosphere or by the planet’s surface. Daytime clouds reflect sunlight back into space and thus have a cooling effect. Nighttime clouds have a warming effect on the surface and a cooling effect in the upper atmosphere due to the Greenhouse effect of the water vapor in the cloud. As we will see, much of the argument between the various scientific camps (‘warmists’, ‘luke warmers’ and ‘flat liners’) involves the roles of clouds in atmospheric temperature.
Question 5: Nature releases carbon dioxide into the atmosphere. Humans release carbon dioxide into the atmosphere. How much of atmospheric carbon dioxide release is due to humans? How much is due to nature?
Answer: The following are estimates and are not accurately measured numbers:
Nature: 210 billion tons per year (96% of total)
Humans: 9 billion tons per year (4% of total)
Source: Wikipedia – Carbon Cycle
Question: Atmospheric carbon dioxide levels are believed to have risen from 280 ppm before the Industrial Revolution to its current level of 395 ppm. If this rises to 500 ppm (a 25% increase from 395 ppm), wouldn’t this increase carbon dioxide’s contribution to the greenhouse effect by 25%?
Answer: No; however, this is another point of contention between the various camps.
Remember that the Greenhouse Effect involves the absorption of infrared energy. The Beer-Lambert equation (also called Beer’s law) tells us that the amount of electromagnetic energy (including infrared) absorbed increases logarithmically with the amount of the absorbing substance, not linearly. Some calculations:
Log (280) = 2.45 Note: 280 is the carbon dioxide level before the Industrial Revolution)
Log (395) = 2.60 Notes: 1) 395 is the current level; 2) 395 is a 41% increase over 280; 3) this 41% increase in atmospheric CO2 levels increases CO2’s absorption of IR radiation by 6%
Log (560) = 2.75 Notes: 1) 560 is a doubling of the pre-Industrial Revolution atmospheric carbon dioxide level; 2) The increase in CO2’s Greenhouse Effect is = 12.2% over the pre-Industrial Revolution amount.
However, the ‘warming’ model assumes that the increase in the Greenhouse Effect due to increased atmospheric CO2 is 3 times higher than is calculated by the Beer-Lambert equation. The reasoning is as follows:
1) As atmospheric CO2 levels increase, the amount of the Greenhouse Effect due to CO2 increases. (Note: nobody disputes this).
2) As the Greenhouse Effect increases (due to increases in atmospheric levels of CO2 and other greenhouse gases), global temperature will rise. (Note: this is reasonable, but not necessarily universally accepted).
3) As global temperatures increase, the amount of water that evaporates from surface water (lakes, oceans, etc.) increases. (Note: nobody disputes this).
4) The extra water vapor produced by the increase in temperature from the increased greenhouse effect due to the increased atmospheric carbon dioxide levels will increase the overall greenhouse effect, which will lead to higher global temperatures. (Note: this is the key issue in the scientific dispute).
The skeptics’ argument as to why this model isn’t realistic:
Now we are back to the cloud issue. Skeptics argue that the higher levels of water vapor will produce more clouds, which will reduce the amount of sunlight that reaches Earth’s surface (due to the increased reflection of sunlight by the clouds), thus offsetting the enhanced greenhouse effect due to the increased water vapor.
Question 6: We know that the glaciers are melting; doesn’t this fact prove that climate change has occurred?
Answer: We know that a major climate change occurred about 10,000(?) 12,000(?) years ago when the last ice age ended. Glaciers have been melting since this global warming event began. We know that during the past ice age, virtually all non-tropical land masses were covered in glaciers.
One of the arguments between the ‘warmers’ and the ‘skeptics’ is whether or not climate change events such as the Medieval Climate Optimum and the Little Ice Age did- or did not- actually occur. If the Little Ice Age did in fact occur, as has been indicated by historical records, then presumably natural warming occurred during the 18th century that ended the Little Ice Age. There is some evidence of glacier advancement during the Little Ice Age that ended and was reversed at the end of the Little Ice Age.
Question: AARGH! At least we know how temperature changed during the 20th century, don’t we?
Answer: This is another point of contention. The problem is how ground-based temperatures were (and still are) measured. The issues are where the temperatures are measured, how they are measured and how much the temperatures are being influenced by near-by heat sources such as urbanization, pavement and possibly even cooking grills.
Skeptics argue that the only reliable temperature record is the one that uses data from weather satellites, as these avoid the problems discussed. Warmists tend to discount the satellite temperature record. The latest satellite-based temperature record is shown below; it should be noted that this data begins in 1979 as this was when the first satellite was launched. The ‘zero point’ on the horizontal axis is the average of this data from 1981 – 2010; when the line is above zero, the temperature is warmer than this 30 year average; when it is below, the temperature is lower than this 30 year average.
Note that although July 2012 may have been the warmest July in the US during the time period that modern temperature records have been produced, globally, July 2012 was 0.28o C warmer than the average global temperature during 1981 to 2010.
Models, Temperature Predictions and Realties
Warmists argue that their Global Climate (computer) models accurately describe Earth atmosphere and that the models’ predictions of future temperatures are accurate. Skeptics argue that the models do not accurately describe Earth atmosphere, particularly with respect to clouds and that the past predictions were not accurate. ♦
DR. NAIL is Chair of the Chemistry Department at Oklahoma City University