Satellites Suggest Rising Tropical High Cloud Altitude: 2002-2021

Tropical upper-troposphere clouds are expected to rise under global warming, contributing a positive radiative feedback. Here we show that Moderate Resolution Imaging Spectroradiometer (MODIS) retrievals over 2002-2021 from the Terra and Aqua satellites report a tropical-mean high-cloud altitude increase of 6.9 +/- 2.7 m yr(-1) (+/- 2 sigma), while atmospheric models report 5.6 +/- 3.0 m yr(-1) over 1979-2014. During their common overlap period, however, the observed trend is greater than that of the models. The atmospheric models also show a tropically confined cloud-height response to El Nino, whereas the observed cloud height response peak extends into the subtropics. Poleward of the mid-latitudes, Aqua and Terra MODIS have cloud-height drifts relative to each other, highlighting the need for deeper investigation of potential time-dependent biases in MODIS cloud retrievals. Both sensors report significant tropical cloud height increases since 2002, which are statistically consistent with those simulated by climate models.

Automated summary

Tropical upper-troposphere clouds are expected to rise and contribute to positive radiative feedback under global warming. A comparison between satellite retrievals and atmospheric models shows that the observed trend of cloud altitude increase is greater than that of the models. The observed cloud height response extends into the subtropics, which is different from the models' prediction. Further investigation is needed to explore the time-dependent biases in MODIS cloud retrievals.