Reference Atmospheric Temperature Trends Observed from Satellites in Stable Orbits

Atmospheric temperature time series developed from satellite microwave sounder observations has been extensively used in climate change monitoring and verifying climate model simulations of climate change. However, uncertainties exist in the satellite merged products and their resulting atmospheric temperature trends, mainly caused by diurnal sampling changes over time and instrument calibration errors. Satellite products developed by different research groups produced different atmospheric temperature trends, undermining the capability of using satellite observations in global change monitoring. Here we develop a post-millennium mid-tropospheric temperature time series from continuous observations by advanced microwave sounders onboard satellites in stable sun-synchronous orbits, including Aqua, MetOp-A, S-NPP, and NOAA-20. Such observations have high radiometric stability and do not experience diurnal sampling changes over time, allowing us to develop merged time series from multiple satellites with an accuracy better than 0.01 Kelvin per decade in trend detection. This accuracy in trend detection exceeds the measurement stability requirement of 0.02 Kelvin per decade given in GCOS (2016) for deep layer atmospheric temperature time series. With such high accuracy, the resulting time series can be used as a reference measurement of climate variability and trends in atmospheric temperatures. The warming rate from this time series for the atmospheric layer between surface and 10 km is 0.23±0.13 Kelvin per decade during the period from 2002 to 2020, which is ~14% higher than the existing satellite microwave sounder datasets. This reference measurement is expected to help reconcile differences in climate trend comparisons among different satellite products and between climate model simulations and satellite observations during the post-millennium periods. It may also be helpful in the development of atmospheric temperature time series with a better accuracy for satellites before the millennium when used as a reference.