OS049-08
Regional sea level pressure trends: Model-based assessment of detection, attribution, and consistency with CMIP5 historical simulations.
Regional sea level pressure trends: Model-based assessment of detection, attribution, and consistency with CMIP5 historical simulations.
Wednesday, 16 December 2020: 09:19
Virtual
Abstract:
Observed sea level pressure (SLP) trends for 1901-2010, 1951-2010, and 1981-2010 are assessed
using two observed data sources (HadSLP2_lowvar and 20CRv3) compared to a CMIP5 multi-model
ensemble. The CMIP5 simulations include runs with: i) no external forcing (Control runs), ii) natural
external forcing only (Natural-Forcing), or iii) natural plus anthropogenic forcings combined (All-
Forcings). We assess: i) whether the CMIP5 All-Forcing ensemble is consistent with observations; and ii)
whether there is model-based evidence for detectable anthropogenic influence for the observed SLP
trends.
For the 1901-2010 and 1951-2010 trends, a robustly detectable anthropogenic signal in both
observational datasets is a zonal band of SLP increase extending over much of the southern hemisphere
extratropics (30oS-50oS). In contrast, the HadSLP2_lowvar and 20CRv3 observed datasets disagree on
the sign of the century-scale trends in SLP over much of the low-latitude region 25oN-25oS. These
differences will limit confident detection/attribution/consistency conclusions for lower-latitude regions
at least until the observational data product discrepancies are better reconciled. The northern
hemisphere extratropics remains a difficult region for identifying any detectable anthropogenic
influence for annual- or seasonal-mean SLP trends. Overall, our results highlight the difficulty in
detecting and attributing anthropogenic signals in SLP for relatively short time scales. The observed
1981-2010 regional trends typically have a different pattern and magnitude from the simulated
externally forced trends. Consequently, our results suggest that internal variability is likely the dominant
driver of most observed 1981-2010 regional trend features, including the pronounced increase in SLP
over the central and eastern equatorial Pacific.
using two observed data sources (HadSLP2_lowvar and 20CRv3) compared to a CMIP5 multi-model
ensemble. The CMIP5 simulations include runs with: i) no external forcing (Control runs), ii) natural
external forcing only (Natural-Forcing), or iii) natural plus anthropogenic forcings combined (All-
Forcings). We assess: i) whether the CMIP5 All-Forcing ensemble is consistent with observations; and ii)
whether there is model-based evidence for detectable anthropogenic influence for the observed SLP
trends.
For the 1901-2010 and 1951-2010 trends, a robustly detectable anthropogenic signal in both
observational datasets is a zonal band of SLP increase extending over much of the southern hemisphere
extratropics (30oS-50oS). In contrast, the HadSLP2_lowvar and 20CRv3 observed datasets disagree on
the sign of the century-scale trends in SLP over much of the low-latitude region 25oN-25oS. These
differences will limit confident detection/attribution/consistency conclusions for lower-latitude regions
at least until the observational data product discrepancies are better reconciled. The northern
hemisphere extratropics remains a difficult region for identifying any detectable anthropogenic
influence for annual- or seasonal-mean SLP trends. Overall, our results highlight the difficulty in
detecting and attributing anthropogenic signals in SLP for relatively short time scales. The observed
1981-2010 regional trends typically have a different pattern and magnitude from the simulated
externally forced trends. Consequently, our results suggest that internal variability is likely the dominant
driver of most observed 1981-2010 regional trend features, including the pronounced increase in SLP
over the central and eastern equatorial Pacific.