This calculation is meant only to quantify how much greenhouse-gas changes could raise the global average temperature, compared with the detected rise. We'll use relative-effectiveness data from the following source:
Monitoring Solar Radiation and Its Transmission Through the Atmosphere
© David R. Brooks, Research Professor
Department of Mechanical Engineering and Mechanics
Drexel University, Philadelphia, PA, USA
President, Institute for Earth Science Research and Education, Norristown, PA USA
Principal Investigator, The GLOBE Program's Aerosols, Water Vapor, and UV-A Monitoring Projects
http://www.pages.drexel.edu/~brooksdr/DRB_web_page/papers/UsingTheSun/using.htm#wv
It's possible that other investigators could assign different values. But, for the purpose of this calculation, the values used don't have to be exact.
We'll use concentration data from this source:
EOS Vol. 80, No. 39, September 28, 1999, p. 453.
Climate Change and Greenhouse Gases
Authors:
Tamara S. Ledley, Eric T. Sundquist, Stephen E. Schwartz, Dorothy K. Hall, Jack D. Fellows, and Timothy L. Killeen
The data is taken from this chart, shown in their article:
The mean temperature of the atmosphere is about 60 deg F or 15 deg C, at which the maximum amount of water vapor is 1.8% or 18,000 parts per million (ppm) [Keenan and Keyes, "Thermodynamic Properties of Steam"].
Now, we'll assume water-vapor and ozone concentrations don't change and calculate the greenhouse effect for conditions in 1850 and 2000.
Greenhouse Effect for 1850| Greenhouse Gas | Concentration (ppm) | Effectiveness Relative to CO2 | Effectiveness times concentration |
| Water | 18,000 | 0.1 | 1800 |
| Carbon Dioxide | 280 | 1 | 280 |
| Methane | 0.8 | 30 | 24 |
| Nitrous Oxide | 0.27 | 160 | 43 |
| Ozone | 0.04 | 2000 | 80 |
| Chlorofluorocarbons | 0 | 23,000 (Avg) | 0 |
| TOTAL | 2227 |
| Greenhouse Gas | Concentration (ppm) | Effectiveness Relative to CO2 | Effectiveness times concentration |
| Water | 18,000 | 0.1 | 1800 |
| Carbon Dioxide | 365 | 1 | 365 |
| Methane | 1.7 | 30 | 51 |
| Nitrous Oxide | 0.31 | 160 | 50 |
| Ozone | 0.04 | 2000 | 80 |
| Chlorofluorocarbons | 0.0004 | 23,000 (Avg) | 9 |
| TOTAL | 2355 |
So, the total effectiveness-times-concentration has risen from 2227 to 2355, or 5.7%
We know that the greenhouse effect is about 33 deg C [REF]; that is, Earth would be 33 deg C cooler if there were no greenhouse effect. So, based on our simplified calculation, we would expect the temperature to rise 5.7% of 33 deg C, or 1.9 deg C.
The calculation doesn't account for time-lag effects or a lot of other things. On the other hand, it is highly conservative; the concentration of water vapor is overstated, which means we're understating the relative influence of the other greenhouse gases. The numbers shouldn't be taken literally, but this simple calculation does show that the increase in greenhouse-gas concentrations more than accounts for the 0.7 deg C temperature rise.
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