W.A. van Wijngaarden and Will Happer calculated the CO2 climate sensitivity – or the temperature increase when CO2 doubles – is 2.2 K for a fixed relative humidity. This means global warming caused by increased CO2 is insignificant.
See the green line in their Figure 4, also shown above? The green line is the atmosphere without CO2. The black line is CO2 at 400 ppm. The red line is CO2 at 800 ppm. CO2 at 300 ppm would show no significant difference from the black line. So, doubling the CO2 concentration has no effect on global warming.
Climate alarmists have been crowing about nothing. CO2 heating is a figment of their imagination.