The alarmist counter-argument is that increasing CO2 concentration increases the 'radiative height', and if the lapse rate remains constant, increases the surface temperature. There is a more fundamental reason why increasing CO2 concentration has negligible effect, and that is because the greenhouse effect is thermodynamic nonsense. Even greenhouses don't work by the 'greenhouse effect', they work by the suppression of convection. Also the atmospheric transparency data on which the whole myth rests relates to attenuation along sight lines. Attenuation occurs because energy is scattered out of the line of sight. The green house effect is based on the erroneous belief that greenhouse gases 'block' the radiation, and the blocked radiation heats up the atmosphere. When applied to an atmosphere layer, that contravenes Kirchoff's Law, which is essentially a re-statement of the First Law of Thermodynamics. Thus, belief in the 'greenhouse effect' is equivalent to a belief in perpetual motion machines.

Superbe. It's useful to note that the first example, 100ppm, is the extinction level for plant life (and thus animal life). Red, therefore, is the perfect color to represent the TRUE alarm value for levels of CO2.