Contribution of stratospheric cooling to satellite-inferred tropospheric temperature trends Quiang Fu, Celeste M. Johanson, Stephen G. Warren & Dian J. Seidel NATURE | VOL 429 | 6 may 2004 pp. 55-58 Outline • The Microwave sounding unit (MSU) Measurement principle • Tropospheric temperature trends derived from satellites • Discrepancies between surface and satellite measurements • Reason for popular and scientific discussions about climate change • Reconciliation by this paper… MSU • nadir viewing instrument • 4 microwave channels (50-57.9 GHz) • measures brightness temperature according to Planck‘s law: Radiative transfer (no scattering) • Simplified radiative transfer (Schwarzschild equation) Weighting function Contribution from the atmosphere Measured intensity Surface Contribution Spectral range • MSU measures at 50.3, 53.74, 54.96, and 57.95 GHz • Oxygen absorption in this region • Each channel has a different optical depth with respect to oxygen RT II Channel 2 -> troposphere Optically thin Optically thick Results from MSU Troposphere Stratosphere (UAH = University at Huntsville, RSS = Remote Sounding Systems) Results II Results II Discrepancies • Surface measurements: 0.17K/decade • MSU (UAH): 0.047K/decade • MSU (RSS): 0.13K/decade • GCM prediction for troposphere: 1.1*surface temperature change (0.187 K/decade) globally Boost for climate change critics… The solution by Fu et al There is still an impact of the stratosphere to T2 (15%) and the stratosphere is cooling!! Correction for T2 necessary: T850-300=a0+a2T2+a4T4 a‘s derived from fits to ballon borne measurements Dependencies of T2 and T4 T4 Stratospheric trend T2 Tropospheric trend 0.18K Tropospheric trend Results Results Trend ratios (troposphere/surface) Globe GCM MSU 1.2 1.1 Tropics 1.54 1.6 Conclusion • Wrong troposheric temperature trend due to the disregard of stratospheric cooling • Simple correction scheme was implemented • New results reconcile surface measurements, MSU measurements and GCM models • ASMU provides now more channels (better height resolution) • Always look on the averaging kernel (esp. for NADIR DOAS measurements) !!