Your Questions & Answers
Thank you to everyone who asked a question about the issues raised in the Great Global Warming Swindle. Here are some of the questions that you asked with Professor Mitchell's answers.Q1 | Q2 | Q3 | Q4 | Q5 | Q6 | Q7 | Q8 | Q9
Question 1
If water vapour is on average about 10,000 ppm vol in air and it's molecule has a greenhouse effect several times that of carbon dioxide, is it not true that carbon dioxide at only 380ppm vol is just totally insignifigant and not relevent to the earth's greenhouse effect? Why do people treat carbon dioxide as a greenhouse gas?
Grant Lockie
Professor Mitchell: Although nitrogen and oxygen are the main gaseous constituents of the atmosphere, they do not absorb radiation at infrared (thermal) wavelengths because they are simple diatomic molecules. It is only triatomic (and more complicated) molecules that absorb infrared radiation and hence contribute to the greenhouse effect.
Question 1
If water vapour is on average about 10,000 ppm vol in air and it's molecule has a greenhouse effect several times that of carbon dioxide, is it not true that carbon dioxide at only 380ppm vol is just totally insignifigant and not relevent to the earth's greenhouse effect? Why do people treat carbon dioxide as a greenhouse gas?
Grant Lockie
Professor Mitchell: Although nitrogen and oxygen are the main gaseous constituents of the atmosphere, they do not absorb radiation at infrared (thermal) wavelengths because they are simple diatomic molecules. It is only triatomic (and more complicated) molecules that absorb infrared radiation and hence contribute to the greenhouse effect.
Water vapour is by far the most important greenhouse gas in the atmosphere today, composing 0.25% its mass, followed at some distance by carbon dioxide and other minor atmospheric constituents. These are estimated to keep the earth some 30°C warmer than it would otherwise be. Venus, which has a dense carbon dioxide atmosphere, is some 400°C warmer than it would otherwise be because of the greenhouse effect.
To put things in perspective, the extra heating due to the increase in greenhouse gas concentrations since the pre-industrial period equates to an approximate 1% change in heating from the Sun. During the same period, the estimated increase in the Sun's heating is around 0.2% (based on surrogate measurements such as sunspots) – only one fifth of the influence from human activity.
Finally, greenhouse gases become less effective per molecule as their concentrations increase because the main wavelengths at which they absorb and re-radiate heat become saturated. This does not mean that further increases in these gases have no further greenhouse effect; just that further increases become less effective at increasing warming. This explains why small increases in relatively scarce atmospheric gases such as methane and CFCS (chlorofluorocarbons) can have the same effect as much larger increases in carbon dioxide.
To put things in perspective, the extra heating due to the increase in greenhouse gas concentrations since the pre-industrial period equates to an approximate 1% change in heating from the Sun. During the same period, the estimated increase in the Sun's heating is around 0.2% (based on surrogate measurements such as sunspots) – only one fifth of the influence from human activity.
Finally, greenhouse gases become less effective per molecule as their concentrations increase because the main wavelengths at which they absorb and re-radiate heat become saturated. This does not mean that further increases in these gases have no further greenhouse effect; just that further increases become less effective at increasing warming. This explains why small increases in relatively scarce atmospheric gases such as methane and CFCS (chlorofluorocarbons) can have the same effect as much larger increases in carbon dioxide.
