To Anonymous Coward
Your arguments concerning the comparative volume of human emissions to natural sources and the relative strengths of water vapor versus CO2 as greenhouse gases are both non-starters.
Water vapor is not a climate driver. It is a feedback mechanism. As mentioned earlier by myself and others, water vapor is cycled through the climatic environment in a matter of days. It simply does not have the atmospheric longevity to drive climate over long periods of time. However, it can very effectively amplify other climate drivers such as CO2 which can remain in the atmosphere for a hundred years or more.
As for CO2, comparing volumes of emissions from natural sources with human sources also does not support your premise as it is the human emissions that are driving up the overall relative composition of CO2 in the atmosphere. Unless there has been a massive and ongoing release of new CO2 by natural sources during the industrialized period (there hasn't), the climate has already adapted to, compensates for, and is in balance with the levels of natural emissions.
Imagine a huge scale with natural climate influences on the left side and the Earth's climatic reactions on the right. So, on the left you have your massive natural CO2 emissions and other GHGs along with solar variability, tectonic and volcanic activity, orbital variations and so on. On the right, you have atmospheric, land, and ocean temperature, relative humidity, ocean alkalinity and so on. Based on changes to the left, the right changes to balance. The amounts on each side may vary through time, but the system strives to keep the balance throughout.
Now, mankind adds a small weight of additional CO2 to the left side. It's paltry compared to the existing weight on the system from natural sources. At first, the system's reaction is negligible and indistinguishable. However, the weight stays there for a hundred years. The next year, mankind adds another weight, adding to the one from the previous year. The next year, another weight. The next year, another, and so on. This continues for a hundred years before that first small weight is removed. It would be bad enough if the weight remained the same each year, but it doesn't. Each year, the weight added by mankind grows. Each, taken individually, can be dismissed, but, taken cumulatively, they are causing the system to react, your four questions not withstanding.