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First, mankind's activities may have something to do with the current rate of warming.

Let's put a number to that "may" shall we?

http://www.clearlight.com/~mhieb/WVFossils/greenhouse_data.html

Just how much of the "Greenhouse Effect" is caused by human activity?

It is about 0.28%, if water vapor is taken into account-- about 5.53%, if not.

This point is so crucial to the debate over global warming that how water vapor is or isn't factored into an analysis of Earth's greenhouse gases makes the difference between describing a significant human contribution to the greenhouse effect, or a negligible one.

Water vapor constitutes Earth's most significant greenhouse gas, accounting for about 95% of Earth's greenhouse effect (4). Interestingly, many "facts and figures' regarding global warming completely ignore the powerful effects of water vapor in the greenhouse system, carelessly (perhaps, deliberately) overstating human impacts as much as 20-fold.

Water vapor is 99.999% of natural origin. Other atmospheric greenhouse gases, carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and miscellaneous other gases (CFC's, etc.), are also mostly of natural origin (except for the latter, which is mostly anthropogenic).

Human activites contribute slightly to greenhouse gas concentrations through farming, manufacturing, power generation, and transportation. However, these emissions are so dwarfed in comparison to emissions from natural sources we can do nothing about, that even the most costly efforts to limit human emissions would have a very small-- perhaps undetectable-- effect on global climate.

Role of Atmospheric Greenhouse Gases
(man-made and natural) as a % of Relative
Contribution to the "Greenhouse Effect"

Based on concentrations (ppb) adjusted for heat retention characteristics	Percent of Total	Percent of Total --adjusted for water vapor
Water vapor	-----	95.000%
Carbon Dioxide (CO2)	72.369%	3.618%
Methane (CH4)	7.100%	0.360%
Nitrous oxide (N2O)	19.000%	0.950%
CFC's (and other misc. gases)	1.432%	0.072%
Total	100.000%	100.000%

Anthropogenic (man-made) Contribution to the "Greenhouse
Effect," expressed as % of Total (water vapor INCLUDED)

Based on concentrations (ppb) adjusted for heat retention characteristics	% of All Greenhouse Gases	% Natural	% Man-made
Water vapor	95.000%	94.999%	0.001%
Carbon Dioxide (CO2)	3.618%	3.502%	0.117%
Methane (CH4)	0.360%	0.294%	0.066%
Nitrous Oxide (N2O)	0.950%	0.903%	0.047%
Misc. gases ( CFC's, etc.)	0.072%	0.025%	0.047%
Total	100.00%	99.72	0.28%

In seeing all this discussions on global warming, I've never yet read anything by any astronomer who treats global warming as fact. There are just far too many variables and wrong assumptions made by the global warming crowd-- for instance, most people use as their mathematical model as the Earth being a perfect sphere that rotates at a constant speed through a perfect elliptical orbit around a sun whose output is perfectly constant. Small tiny variations in the solar output (totally beyond our control) produce huge changes here.

Like you've pointed out, the Earth is not as fragile as some would have us believe. (I guess GW fits into the "man is evil" mantra held by many).

Thanks for the information, but it may surprise you to know that I am aware that water vapor is the most significant greenhouse gas.

However, I hope it doesn't surprise you to know that the major change in radiative forcing, which may affect the concentration of water vapor in the atmosphere, is due to increasing greenhouse gas concentrations. If the feedback effect on atmospheric water vapor is positive and not negative -- and that's still VERY uncertain -- then the radiative forcing effects of increasing greenhouse gas concentrations will be augmented.