Ken, I am going to just skip over your mislabeling of me and my position and go to the science where you are missing an important point. You posted
So, without any evidence you want to claim that Milankovitch cycles - that act very slowly over 10's of thousands of years - are responsible for significant changes to Antarctic ice sheets within the last century, that they are a significant factor in the current observable rapid acceleration of ice mass loss. You are arguing without evidence that there is a significant natural component to Antarctic ice mass loss, that therefore attribution to human causes is exaggerated.
What you seem to be missing is that there is strong evidence that that Milankovitch Cycles play a major role in the ice age / warm interglacial periods that dominate
the earth's climate over the last few million years. (But I am not
claiming that they dominate now, after humans have had substantial impacts.) In particular, the geologic evidence is that there was a huge amount of ice melt, starting about 25,000 years ago, when there were ice sheets (similar to what is now on the Antarctic and Greenland areas) that covered much of North America and northern Europe/Asia. Ice sheets 2 miles thick melted over a period of a maybe 10,000 years, raising the ocean level by about 325 feet. Then, the sea level became more stable, but not perfectly static.
So, without any effect from human industrializatiton
, Earth has previously and relatively (geologically) recently experienced rapid melting of large ice sheets. And, in previous warm periods over the last few million years, the sea level reached higher than it is now by several tens of feet, before going back down again as the northern continents began building ice sheets, again. I don't have numbers handy for the peak sea level rate of rise during the last big melt, but if it was averaged over 10,000 years, it would be 0.4 inch per year. So, it is a good bet that the peak rate was in the inches per year range. With some of the huge ice dam breach theories for those melts, it isn't unlikely that there were episodes where sea level may have risen by feet in a year.
Those interglacial sea level records indicate that there was a lot of variablity in the warm periods, so the geologica record really doesn't help us precisely
predict what would have happened during the current warm period if humans had not had any effects. And, the last I looked, nobody has made a computerized climate model that can "backcast" the climate to match the geological evidence. So, we are not in a good position to say exactly what the climate would be doing right now
if humans were not here, doing what we are doing and have already done.
About the best geologic evidence for the net effects of human impacts comes from comparison of atmospheric CO2 levels over the last 10 million years. Before the ice age cycles that started about 3 million year ago, there was more CO2 in the atmosphere. And there was different circulation in the ocean. In particular, the Central American isthmus had not risen above the sea level then
, so the Atlantic and Pacific were connected between South and North America. It is theorized that a combination
of CO2 removal by rock weathering and changes in atmospheric and oceanic circulation patterns is what started the ice age cycles (with both having been driven by techtonic activity raising mountains). And, the cold periods had been getting stronger, having started with warm periods roughly every 50,000 years, they started skipping warm periods and went to one roughly every 100,000 years about 900,000 years ago. So, humans arteficially increasing CO2 in the atmosphere is believed to be a major disruption of that cycle process. Because the current CO2 levels are approaching the levels that occurred before the ice age cycles began several thousand years ago, it is reasonable to think that human activity may have ended the ice age cycles.
So, it is reasonable to believe that the average
climate will go back to something similar to what existed several million years ago. That would mean sea level hundreds of feet higher than it is right now, maybe as much as 300 feet higher. That will, by itself, wipe out most of our current technological infrastruture. And the climate will change to make Canada and Russia more pleasant and productive, while having negative effects on tropical regions.
But, that will take hundreds to thousands of years. Humans can adapt, and human cultures can adapt. The big question is will we adapt in a constructive or destructive manner. History seems to indicate that we are our own worst enemies, and will tear down each other's civilizations as we compete for resources. That might mean the end of things like space telescopes and the return to a brutal existence for surviving humans.
How humans fare in the changing environment is of course the main topic for human discussions. But, Earth has gone though much more cataclysmic events, and life has persisted and evolved in spite of them, and maybe even because of them. So, I am not agreeing with the people who think we are about to turn Earth's environment into something like what we see on Venus.