Tropical vertical temperature trends: A real discrepancy?



[1] We examine the sensitivity of modeled and observed tropical tropospheric temperature trend amplification (the ratio of T2LT “lower troposphere” to surface changes) to several sources of uncertainty. Model behaviour is robust across a large perturbed physics ensemble of HadCM3, yielding a smaller amplification range (1.44 ± 0.06) than a previous multi-model ensemble (1.41 ± 0.24). The uncertainty of inter-satellite calibration implied by available MSU T2 (mid-troposphere) estimates (σ = 0.035K) is much greater than that required to adequately resolve the trend (σ < 0.01K), or the amplification behaviour (implied amplification range ±0.95). Trend amplification uncertainty in both models and observations decreases as the timescale increases. Depending upon choice of dataset and time period, uncertainty in trend amplification estimates over 21 years lies between ±1.5 and ±0.2.