CO2 as a global thermostat

While much has been said about the major role of water vapor and clouds in the greenhouse effect, the title linked article by NASA climate scientist, Andrew Lacis, describes a sophisticated modeling experiment that zeroed out atmospheric CO2 and other non-condensing greenhouse gases, so that water vapor and clouds were the only atmospheric greenhouse factors. The net result was a frozen planet with temperatures even at the Equator of just 1 deg C.

From the title article:
"This climate modeling experiment was performed using the GISS ModelE general circulation coupled atmosphere-ocean climate model by zeroing out all of the non-condensing greenhouse gases. Doing this removed the radiative forcing that sustains the temperature support for water vapor and cloud feedbacks, causing rapid condensation and precipitation of water vapor from the atmosphere, collapsing the terrestrial greenhouse effect, and plunging the Earth into an icebound state."

From a 2nd NASA article we get a geological perspective:
"The study ties in to the geologic record in which carbon dioxide levels have oscillated between approximately 180 parts per million during ice ages, and about 280 parts per million during warmer interglacial periods. To provide perspective to the nearly 1 C (1.8 F) increase in global temperature over the past century, it is estimated that the global mean temperature difference between the extremes of the ice age and interglacial periods is only about 5 C (9 F).

"When carbon dioxide increases, more water vapor returns to the atmosphere. This is what helped to melt the glaciers that once covered New York City," said co-author David Rind, of NASA's Goddard Institute for Space Studies. "Today we are in uncharted territory as carbon dioxide approaches 390 parts per million in what has been referred to as the 'superinterglacial.'"

So what to do if the Earth's temperatures rise dramatically, with associated sea level rise, drought, famine, disease, etc. Reducing atmospheric CO2 levels seems to be an unachievable task, at least in the next century. So what can we do? Is Geoengineering a viable approach???? (stay tuned)