Abstract: In this paper, the effeCts of increased CH₄, N₂O and CO₂ due to human activities on the upper stratosphere and mesosphere are investigated using a coupledchemical-radiative one-dimensional model. The results indicate that a doubling inthese gases leads to an obvious variation of water vapour and ozone concentrationsand temperature in the middle atmosphere. The temperature in the upper part ofmiddle atmosphere will decrease about 10K due to a doubling in troposphericCO₂. And a doubling CH₄concentration in the troposphere not only lead to anincrease in water vapour concentration of more than 50% in the mesopause region, but also decrease its temperature obviously. It could be in favour of the formation of nocticlucent cloud.