I once had a discussion with a Ph.D. at a university regarding global warming. His answer was interesting and something that I do not see addressed commonly in global warming discussion. He basically stated that when we change the biomass on a piece of land, such as a large tract of land and turn into a farm which we irrigate and make highly productive, or even our lawns, that what we are doing is increasing the amount of land that will absorb CO2. However, when these plants die, they decompose and then release that CO2. So, in essence, since the population of earth has become so large, over the past few hundred years globally, that we have continuously increased the total area on earth that has become 'managed irrigated lands' and have continuously been locking up more and more CO2 per year in these lands which is released later in the year when the crops are harvested or the plants die off. Another point on global warming that I would like to add that seems to be missed: Global warming has been going on since the end of the last ice age, after all that's why the ice age ended.