Mid-tropospheric temperature soundings over tropical oceans by the Atmospheric Infrared Sounder, AIRS, using 4.3 micron CO2 R-branch and P-branch channels independently measure about 260 K with one Kelvin semi-annual variability. The difference between the soundings, which cancels seasonal variability, has increased over the past two years by 47 ¿ 9 mK/year. This trend is explained by the increase of 2.2 ¿ 0.4 ppmv/year and 0.6 ¿ 0.2 ppbv/year in the abundance of CO2 and N2O, respectively, which results in a 35 mK/year trend. The ability to achieve closure at this level with only two years of AIRS data is very encouraging for measurements of other trends of atmospheric temperatures relevant to climate research. AIRS covers the 3.7 to 15.4 micron region with spectral resolution of λ/Δλ = 1200. AIRS was launched into a polar 705 km altitude orbit on the EOS Aqua spacecraft on May 4, 2002, and has an expected on-orbit lifetime of seven years.