Contingencies Online - November/December 2009

Letters continued

Nature has a way of slapping our hands when we meddle. Already two unforeseen products of reducing air pollution (the Clean Air Act?) are recognized:

■ Reduced biomass—There’s less light dispersion so plant understories are receiving less light (energy) and processing less CO2;

■ Faster global warming—More light (energy) is directly penetrating the atmosphere and striking the earth’s surface, turning into heat.

Hindsight says both of these effects should have been foreseen; they are fairly obvious. Politically correct journalism suggested less volcanic activity as the cause of clean air, but I’m sure active actuaries will want to check the facts—I’m 87 and retired.

An applicable axiom of mathematics is that you can’t solve a problem until it’s properly stated. Ask why, in all that’s been written about global warming, life’s dependence on CO2 is never mentioned. Wake up and smell the roses! They also need CO2!

John H. Beales Jr.

Waukegan, ill.

1.0

Observed temperature
Natural forcings
Anthropogenic and natural forcings

temperature Change, Centigrade

0.5

0.0

-0.5

1900 1920 1940 1960 1980 2000 - 1.0

aDaPteD from “ComBinations of natUral anD antHroPogeniC forCings in t WentietH-CentUry Climate,”

JOURNAL OF CLIMATE 17, no. 19 (2004): 3723. rePrinteD WitH Permission.

year

charting climate change

In Susan Woerner’s article (“Managing the Risk of Climate Change”) in the July/August issue of Contingencies, I was puzzled by the chart on Page 50 showing rising temperatures through the 20th century and two other lines showing “forcings.” How are the forcings related to the temperature observations and the temperature scale on the vertical axis? The author states the chart reinforces the human factor in climate change and that the temperature “observations cannot be explained without considering the human influence.”

The choice of years shown in the chart was also puzzling. Does the chart extend to 2005 temperatures and forcings (the red and black lines) or just to 2000 (the blue line)? Since the article underlying the chart was published in 2004

and first submitted in 2003, how could the chart show 2005 temperatures?

I obtained the underlying Journal of Climate article, from which the reader can learn the following:

■ The article is a study of climate models, the assumptions (forcings) that are input into the models, and simulation runs of those models.

■ The study considers only five factors that can influence temperature. There are only two “natural” factors considered: solar and volcano. How solar is factored into the models isn’t described in the article. One may surmise that the article’s authors have concluded that other natural factors, such as clouds, have no impact on temperatures.

■ There are three anthropogenic factors (forcings) considered in the study. One of the factors is a large category of items labeled greenhouse gases, which, according to an accompanying table, include carbon dioxide, several other gases, and water vapor. Presumably, the authors are using measures of all these gases and not just the proportions caused by human activity. No mention is made of the human-caused, or anthropogenic portion, although the Journal

article and the graph in Contingencies both refer to all of the greenhouse gas effects as anthropogenic. Is water vapor now a human-caused greenhouse gas? The other anthropogenic forcings considered are sulfate aerosols and ozone. ■ The five factors are assumed and then simulated in the climate models. Their effects are isolated within the models, and the authors derive variance statistics to see which of the forcings are most correlated with observed temperatures. Some possibilities seem not to have been considered: ( 1) There are other important factors and combinations of factors, ( 2) the forcings assumed may be incorrect and may change over time, ( 3) the assumed human-caused portion of greenhouse gases may be incorrect, ( 4) measurement error, and ( 5) correlation isn’t causation.

The observed temperatures used in the study appear to have been from the 1890-to-2000 period. From my reading of the Journal article, I believe the lines in the graph in the Contingencies article should stop at the year 2000.