Middle Atmosphere Temperature Trends in the Twentieth and Twenty‐First Centuries Simulated With the Whole Atmosphere Community Climate Model (WACCM)

Abstract

We use Whole Atmosphere Community Climate Model simulations made under various climate change scenarios to study the evolution of the global‐mean temperature trend in the late twentieth century and the twenty‐first century. Results are compared with available satellite observations, including new trend estimates derived from the Sounding of the Atmosphere using Broadband Emission Radiometry instrument on NASA's TIMED spacecraft. Modeled and observed trends are shown to be consistent throughout the entire middle atmosphere, from near the tropopause (~16 km) to the lower thermosphere (~95 km) in the period covered by the satellite data. Simulations are extended into the twenty‐first century to document the evolution of the global‐mean temperature trend profile. We find, consistent with previous studies, a marked change in the trend profile at the turn of the twenty‐first century, which is driven by the recovery of stratospheric ozone following the adoption of the Montreal Protocol. In the twenty‐first century, the trend profile becomes more uniform with altitude, but its overall shape and magnitude are conditioned by the scenario adopted for future emissions of greenhouse gases. Our results suggest that the vertical profile of temperature trends in the middle atmosphere will remain an important signature of global climate change, and they underscore the importance of global, continuous monitoring of this region of the atmosphere.

Radiometric Stability of the SABER Instrument

“…As the modeled and SABER‐derived trends below 100 km are less than 1 K per decade (Garcia et al, ), SABER stability is a factor to be considered in overall trend uncertainty and in future instrument design (discussed below). We also note that lower stratospheric trends derived for SABER data (Garcia et al, ) over the 50°N to 50°S latitude region appear consistent with the global lower stratosphere trends presented in Khaykin et al [), further supporting the case for SABER's stability. The SABER team will continue to monitor SABER's performance relative to COSMIC and will investigate stability as a function of latitude in a future publication in order to complement the quasi‐global annual averages shown here.…”

“…The SABER radiometric stability in the stratosphere will also apply throughout the mesosphere and lower thermosphere. As the modeled and SABER‐derived trends below 100 km are less than 1 K per decade (Garcia et al, ), SABER stability is a factor to be considered in overall trend uncertainty and in future instrument design (discussed below). We also note that lower stratospheric trends derived for SABER data (Garcia et al, ) over the 50°N to 50°S latitude region appear consistent with the global lower stratosphere trends presented in Khaykin et al [), further supporting the case for SABER's stability.…”

Long‐Term Trends and Solar Responses of the Mesopause Temperatures Observed by SABER During the 2002–2019 Period

“…The period of measurements is not identical in these results, hence, which could lead to different trends in magnitude obtained by different investigators. However, with the Whole Atmosphere Community Climate Model (WACCM) simulations, Garcia et al (2019) reported that the mesopause trend increases substantially and becomes comparable to the trend at lower levels in the early 21st century, especially between 1995 and 2015. They suggest this change in the trend profile is a characteristic signature of climate change in the middle atmosphere caused by the greenhouse gas.…”

Introduction to Special Issue on “Long‐Term Changes and Trends in the Middle and Upper Atmosphere”

“…The mesopause temperature at midlatitudes has been cooling since 1990 at a rate of about 2°per decade but becomes less significant after 2000. This is somewhat contradictory to the global mean temperature trend in Garcia et al (2019): The mesosphere and lower thermosphere cooling is more substantial after 2000.…”

“…Similarly, MJO modulates planetary wave propagations in the stratosphere (Yang et al, ). As Garcia et al () pointed out, trace gas changes such as ozone in the stratosphere have fundamental impact on the temperature trend in the mesosphere and above. Any modulation of the stratospheric ozone and BDC by QBO, ENSO, and MJO can induce further changes in the upper atmosphere and complicate the detection of long‐term trend signals.…”