The possible effects of future increase in methane emission on the stratospheric water vapor and global ozone

Using a statcof-thcart,fully coupled chemistry climate model-Whole Atmosphere Community Climate Model 3 (WACCM3),the impact of increasing surface emissions of methane (CH4)on stratospheric water vapor and global ozone is investigated.Relative to surface emissions of UHUs in 2000 year, a 50% increase in CHI surface emissions (corresponding to the 2050 value according to the IPCC A1B scenario) will cause an average increase of -0.8×10-6 in water vapor in the stratosphere.The radativc heating effect of increasing CHI on the tropopause contributes 12% to the stratospheric water vapor increases, and the chemical process explains the rest water vapor increases.It is found that the transformation of CH4 into water vapor is more efficient in the southern hemisphere stratosphere than in the northern hemisphere stratosphere.1.63 mol H2O molecule; in the southern hemisphere; 1 mol CH4 molecule may transform into 1.82 mol H2O molecule.The 50% in crease in the CH4 emission would lead to an overall increase of total column ozone(TCO) by 1%-3% at the lower-mid latitudes as well as at the northern high latitudes, and a maximum increase of -8% at the southern high latitudes, with a maximum growth rate of up to -20% over Antaretic in autumn.It is found that the significant TCO increase over Antaretic is mainly caused by a feedback of chemical effect.However, at the northern high latitudes the TCO increase is mainly related to the impact of water vapor increases caused by the oxidation of CH4 on ozone.The study also showed that the effect of increasing methane emissions in the future on ozone recovery is as important as the decrease in bromide emissions.