The point is that the environmental argument has been "Save the planet!", when the actual motive is "Save our civilization!" The planet will be fine, because as apex predators, humanity is going to be one of the first species to go extinct with a major environmental change, and then the rest of the biosphere will adapt to our disappearance. Hell, many individual humans will probably be fine, because the ability to run a complex environment-destroying civilization disappears well before all the individual humans do. However, that's cold comfort to people who depend on modern societal conveniences, or the many people who will die.
GP's point is more about intellectual honesty, but there's also a pragmatic bent to it. Many of the people who most reject climate change interventionism might be swayed by a line of argumentation that goes "You care more about the economy than the environment? You won't have an economy if the environment is disturbed enough."
Sure. The ones actually likely to happen on earth top out at about 5-10C warming above present. At that point negative feedback cycles (like the CO2 greening effect mentioned in the article) dominate positive feedback cycles (like release of methane from the arctic tundra, or lowered albedo from ice melting), and the Earth enters a new equilibrium.
The IPCC maintains that a runaway greenhouse effect which turns the earth into say Venus has basically nil chance of being caused by humans:
GP's point is more about intellectual honesty, but there's also a pragmatic bent to it. Many of the people who most reject climate change interventionism might be swayed by a line of argumentation that goes "You care more about the economy than the environment? You won't have an economy if the environment is disturbed enough."