The Logic of Anthropogenic Global Warming

(c) 2022 by Barton Paul Levenson

Global warming deniers often accuse the theory of anthropogenic global warming of being illogical. Of course, many people use "illogical" or "irrational" to mean "doesn't agree with me." But some make it more specific, accusing scientists of indulging in circular reasoning or other specific logical fallacies. To show that the theory can be phrased in strictly logical terms without fallacies, I do just that below. I use the classical syllogism, the same logical style promoted by Aristotle some 2,300 years ago, and still in use around the world.

The syllogism consists of three statements. In order, they are

• the major premise (stating a general assumption),
• the minor premise (stating a specific assumption that falls under the general case), and
• the conclusion (derived from considering the two premises together).

Major premise: All men are mortal.
Minor premise: Socrates is a man.
Conclusion: Socrates is mortal.

The logic for anthropogenic global warming follows. To show that the conclusion is wrong, deniers must show that one or both premises are false, or that the conclusion is wrongly derived. For more on formal logic and the possible logical fallacies, see This tutorial on formal logic.

The Logic of AGW

Syllogism:
If CO₂ is a greenhouse gas, adding more to the air will warm the surface.
More has been added to the air.
The surface should be warmer.
Empirical check: Is the surface warmer? Yes it is. (Hadley Centre CRUTEM, NASA GISS, NOAA NCDC, NCAR (Berkeley Project), Japan Meteorological Agency)

Syllogism:
If the new CO₂ in the air lacks ¹⁴C and ¹³C, it is artificial.
The new CO₂ in the air lacks ¹⁴C and ¹³C.
The new CO₂ is artificial.
Empirical check: Is the new CO₂ lacking in ¹⁴C and ¹³C? Yes it is. (Suess 1955, Revelle and Suess 1957)

Syllogism:
If the new CO₂ is artificial, the present global warming is man-made.
The new CO₂ is artificial.
The present global warming is man-made.
Empirical check: See above.

Syllogism:
If the Earth warms, drought in continental interiors will increase.
The Earth has warmed.
Drought in continental interiors will increase.
Empirical check: Has drought in continental interiors increased? Yes it has. (Dai 2004, Levenson 2015)

Syllogism:
If the Earth warms, seas will rise.
The Earth has warmed.
Seas are higher.
Empirical check: Are seas higher? Yes they are. (Church and White 2011, NOAA 2022)

Syllogism:
If the Earth warms, storms will be more powerful.
The Earth has warmed.
Storms are more powerful.
Empirical check: Are storms more powerful? Yes they are. (Herring et al. 2018, Severinsky 2020)

References

Church, J.A., White, N.J. 2011. Sea-level rise from the late 19th to the early 21st century. Surveys Geophys. 32, 585-602.

Climatic Research Unit 2022. Temperature. https://crudata.uea.ac.uk/cru/data/temperature/, accessed 11/21/2022.

Dai, A., Trenberth, K.E., Qian, T. 2004. A global dataset of Palmer Drought Severity Index for 1870-2002: Relationship with soil moisture and effects of surface warming. J. Hydrometeorol. 5, 1117-1130.

Herring, S.C., Christidis, N., Hoell, A., Kossin, J.P., Schreck, C.J. III, Stott, P.A. 2018. Explaining extreme events of 2016 from a climate perspective. Bull. Am. Meteorol. Soc. 99, S1-S157.

Japan Meteorological Agency 2022. Global Average Surface Temperature Anomalies. https://ds.data.jma.go.jp/tcc/tcc/products/gwp/temp/ann_wld.html, accessed 11/21/2022.

Levenson, B.P. 2015. Accuracy check on predictions of near-term collapse. Brit. J. Sci. 13, 8-20.

NASA Goddard Institute for Space Studies. https://data.giss.nasa.gov/gistemp/, accessed 11/21/2022.

NCAR 2022. Global surface temperatures: BEST: Berkeley Earth Surface Temperatures. https://climatedataguide.ucar.edu/climate-data/global-surface-temperatures-best-berkeley-earth-surface-temperatures, accessed 11/21/2022.

NOAA 2022. Sea Level Trends. https://tidesandcurrents.noaa.gov/sltrends/, accessed 11/21/2022.

NOAA National Centers for Environmental Information 2022. Climate Data Online. https://www.ncei.noaa.gov/cdo-web/, accessed 11/21/2022.

Revelle, R.; Suess, H.E. 1957. Carbon dioxide exchange between atmosphere and ocean and the question of an increase of atmospheric CO₂ during the past decades. Tellus 9, 18-27.

Severinsky, A.J. 2020. Greenhouse gasses' effect on atmospheric temperature increase and the observable effects on ecosystems. Internat. J. Environ. Ecol. Eng. 14, 362-370.

Suess, H.E. 1955. Radiocarbon concentration in modern Wood. Science 122, 415-417.