Maybe it is because I am married to a geologist, but I tend to look at a longer timescale. When the dinosaurs were around CO2 concentrations were up around 3000ppm.
I'm not saying there will be no effects of global warming-- I am claiming that we, and mother nature, will adapt.
We could argue about whether it would be less expensive or better to change our behavior now rather than just adapt later-- last I looked, adapting by (for example) moving inland and abandoning low- lying cities and countries was estimated to be cheaper than spending money to reduce CO2 emissions.