A075-08
Brief overview of regional detection/attribution: temperature, precipitation, sea level pressure, tropical cyclones
Brief overview of regional detection/attribution: temperature, precipitation, sea level pressure, tropical cyclones
Wednesday, 9 December 2020: 16:33
Virtual
Abstract:
Regional detection/attribution findings for climate variables, including temperature, precipitation, sea level pressure, and tropical cyclones are reviewed. Confidence in attributing observed climate variations to anthropogenic forcing varies strongly depending on the variable and region, and is highest for temperature and temperature-related variables.
Main conclusions:
- There is strong evidence for an anthropogenic warming signal covering most of the global area with adequate long-term records. Detectable anthropogenic influence on summertime heat stress has also been documented.
- Anthropogenic decreases in annual precipitation have been identified for the Mediterranean region, and tentatively for northern tropical Africa, southwest Australia, Tasmania, Caribbean, parts of Indonesia, Sri Lanka, parts of Japan.
- Anthropogenic increases in annual precipitation are more prevalent than decreases. These increases have been identified in a number of extratropical land regions, including central/northeast US, parts of northwest Europe, northern Eurasia, northern Australia, and south-central South America.
- Anthropogenic changes in sea-level pressure (SLP) include a zonal band of increase over the southern hemisphere (SH) extratropics, associated with an increase in extratropical SH surface westerlies and likely due in part to greenhouse gas increases and stratospheric ozone decreases.
- There is little convincing evidence for detectable anthropogenic influence on SLP trends in the northern hemisphere (NH).
- There are major differences between century-scale trends in SLP in the HadSLP2_lowvar and 20CRv3 observational data products, especially in low latitudes and extending into NH midlatitudes.
- For tropical cyclones, most long-term (century-scale) indices of landfalling activity show little trend or decreases. An apparent slowdown over U.S. land has been documented. Possible emerging anthropogenic influences include an increase in the global fraction of TCs reaching Cat 3-5 intensity since 1979; a poleward shift of latitude of maximum intensity in the NW Pacific basin; and a spatial pattern of anthropogenic forcing response in tropical storm frequency change. However, further study is needed to gain confidence in detecting anthropogenic influence on tropical cyclones.
Main conclusions:
- There is strong evidence for an anthropogenic warming signal covering most of the global area with adequate long-term records. Detectable anthropogenic influence on summertime heat stress has also been documented.
- Anthropogenic decreases in annual precipitation have been identified for the Mediterranean region, and tentatively for northern tropical Africa, southwest Australia, Tasmania, Caribbean, parts of Indonesia, Sri Lanka, parts of Japan.
- Anthropogenic increases in annual precipitation are more prevalent than decreases. These increases have been identified in a number of extratropical land regions, including central/northeast US, parts of northwest Europe, northern Eurasia, northern Australia, and south-central South America.
- Anthropogenic changes in sea-level pressure (SLP) include a zonal band of increase over the southern hemisphere (SH) extratropics, associated with an increase in extratropical SH surface westerlies and likely due in part to greenhouse gas increases and stratospheric ozone decreases.
- There is little convincing evidence for detectable anthropogenic influence on SLP trends in the northern hemisphere (NH).
- There are major differences between century-scale trends in SLP in the HadSLP2_lowvar and 20CRv3 observational data products, especially in low latitudes and extending into NH midlatitudes.
- For tropical cyclones, most long-term (century-scale) indices of landfalling activity show little trend or decreases. An apparent slowdown over U.S. land has been documented. Possible emerging anthropogenic influences include an increase in the global fraction of TCs reaching Cat 3-5 intensity since 1979; a poleward shift of latitude of maximum intensity in the NW Pacific basin; and a spatial pattern of anthropogenic forcing response in tropical storm frequency change. However, further study is needed to gain confidence in detecting anthropogenic influence on tropical cyclones.