claim: ( 2009 ) have demonstrated recently  – the upper troposphere ( the only place where adding CO2 to the  atmosphere could make any difference to temperature ) is considerably  drier than the models are tuned to expect.
evidence: At the 500 hPa level, the air temperature averages −7 °C ( 18 °F ) within the tropics, but air in the tropics is normally dry at this height, giving the air room to wet-bulb, or cool as it moistens, to a more favorable temperature that can then support convection.