Revisiting the Mystery of Recent Stratospheric Temperature Trends

Abstract

Simulated stratospheric temperatures over the period 1979–2016 in models from the Chemistry‐Climate Model Initiative are compared with recently updated and extended satellite data sets. The multimodel mean global temperature trends over 1979–2005 are −0.88 ± 0.23, −0.70 ± 0.16, and −0.50 ± 0.12 K/decade for the Stratospheric Sounding Unit (SSU) channels 3 (~40–50 km), 2 (~35–45 km), and 1 (~25–35 km), respectively (with 95% confidence intervals). These are within the uncertainty bounds of the observed temperature trends from two reprocessed SSU data sets. In the lower stratosphere, the multimodel mean trend in global temperature for the Microwave Sounding Unit channel 4 (~13–22 km) is −0.25 ± 0.12 K/decade over 1979–2005, consistent with observed estimates from three versions of this satellite record. The models and an extended satellite data set comprised of SSU with the Advanced Microwave Sounding Unit‐A show weaker global stratospheric cooling over 1998–2016 compared to the period of intensive ozone depletion (1979–1997). This is due to the reduction in ozone‐induced cooling from the slowdown of ozone trends and the onset of ozone recovery since the late 1990s. In summary, the results show much better consistency between simulated and satellite‐observed stratospheric temperature trends than was reported by Thompson et al. (2012, https://doi.org/10.1038/nature11579) for the previous versions of the SSU record and chemistry‐climate models. The improved agreement mainly comes from updates to the satellite records; the range of stratospheric temperature trends over 1979–2005 simulated in Chemistry‐Climate Model Initiative models is comparable to the previous generation of chemistry‐climate models.

Observed changes in Brewer–Dobson circulation for 1980–2018

“…The SH cell of the BDC is strengthening, weakening, and strengthening, respectively, for 1980-1999(large in August), 2000-2018(large in October), and 1980-2018. Figure 5 suggests that the large cooling during October -December in SH high latitudes shown in figure 1 for 2000-2018 is driven by changes of the BDC.…”

“…Thus, the longer record now available suggests that the weakening of the BDC NH cell in the Spring noted by Fu et al (2010), Free (2011), andFu et al (2015), may be only a manifestation of natural variability. The NH cell of the BDC in the Winter is strengthening, weakening, and strengthening, respectively, for 1980-1999 (large in January), 2000-2018, and 1980-2018 (large in January) (see figure 5). The change for 1980-2018 is suggestive of links to the increase of GHGs, assuming that 40 years are long enough to largely average out the impact of the natural variability such as the decadal variation of the North Atlantic Oscillations (e.g.…”

Homogeneity of the Temperature Data Series from ERA5 and MERRA2 and Temperature Trends

“…The next step in utilizing reanalyses should be using them for trend studies. As pointed out in several papers of the SPARC Reanalysis Intercomparison Project (S-RIP) project [23,28], there are problems with the homogeneity of datasets assimilated into reanalyses and it could also affect the time series from reanalyses. [9] used ERA-I, MERRA2, and ERA5 for trend studies during the period 2002-2017.…”

Evaluation of CNRM Earth System Model, CNRM‐ESM2‐1: Role of Earth System Processes in Present‐Day and Future Climate

“…The atmospheric chemistry scheme of CNRM‐ESM2‐1 is Reactive Processes Ruling the Ozone Budget in the Stratosphere Version 2 (REPROBUS‐C_v2), first implemented and evaluated in a former version of CNRM climate model (Michou et al, ), and more recently during the course of the Chemistry Climate Model Initiative (CCMI) research (e.g., Maycock, Matthes, et al, ; Maycock, Randel, et al, ; Morgenstern et al, ; Wales et al, ; Zhang et al, ). It is an “online” scheme whereby the chemistry routines are part of the physics of the atmospheric climate model and called at each time step of the physics.…”