"My own belief is that global warming is 'real,' and is caused by human activity, and that global warming poses a major threat to human civilization."
It is true that climate variation (aka, Global Warming) is real. It is inaccurate to say that it is “caused” by human activity. Climate variation continues apace, as it has done for millennia. Human activity, particularly production of greenhouse gases and modifications of the landscape that affect atmospheric water vapor, modify, to a greater or lesser extent, this natural climate variation.
There are many factors that pose major threats to human civilization, in addition to climate variation. The most immediate threatening factor is Peak Oil, which will change human civilization much sooner and much more drastically than will climate variation.
It is certain that oil will soon become an uneconomical source of energy. It is certain that human civilization is unalterably based on abundant, inexpensive oil and other finite fossil fuels. It is certain that renewable energy sources are less energy dense, less portable and less reliable than fossil fuels. It is certain that no combination of renewable energy sources can replace the amount of energy now consumed by our civilization at present population levels, let alone with any future population growth.
The effects of present and future climate variation are uncertain. Beyond consideration of the accuracy and precision of numerical global climate models, which are only as good as their data inputs, climate variation is chaotic and nonlinear, and thus, virtually impossible to predict with less than hemispheric accuracy over a limited time period.
It seems to me that the one problem facing us, Peak Oil, will cancel out the other, human modified climate variation. Either we will find a way to lower our energy demands and switch to renewable energy sources, thus lowering our “carbon footprint,” or we won’t, thus lowering our “carbon footprint.” The former will allow some maximum cultural continuity, the latter will entail considerable cultural chaos and collapse.
Laid out thusly, in glowing black and white phosphors, the choice seems clear to me. We must do everything we can to lower our energy demands while at the same time using our remaining fossil fuel energy sources to develop as much renewable energy as possible… and here’s the catch: We must accomplish all this without laying waste to the natural biosphere that supports all life on this planet.
It’s a big prescription, to be sure. One way or the other, a thousand years from now, all will be well, as humans will have found a way to live within natural cycles of resource availability and waste assimilation, either by our own determination, or by Nature’s own resolute requirements.