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Recently, the topic of how climate change will affect explosive cyclones has become one of the hottest points in the scientific community. As indicated by Ulbrich et al. (2009), “This increase in interest of the scientific community is partly due to the availability of basically homogeneous gridded datasets for the observational period, which in conjunction with the numerical schemes for the identification of cyclones and the quantification of their activity allow detailed studies that were not possible in earlier times. In addition, many GCM simulations both for present-day climate and climate scenarios have recently become available. Their evaluation with respect to cyclone activity can in principle serve to give confidence in the simulated effects of increasing greenhouse gas forcing on the mid-latitude climate.”
Ulbrich et al. (2009) found that there were two distinct regions of high cyclonic activity over the NH, which could be detected in reanalysis data and modeling results: one over the Northern Pacific and one over the Northern Atlantic, with the secondary center over the Mediterranean. The representation of the latter center was particularly dependent on the spatial resolution of the data and model considered. Under anthropogenic climate change conditions, the number of all cyclones will be decreased in winter, but over some specific regions (the Northeastern Atlantic and British Isles, as well as the Northern Pacific), the number of intense cyclones increases in most models. On average over the hemisphere, the number of extreme cyclones is found to increase only when “extreme” is defined in terms of core pressure, while there is a number decrease in several models when defining “extreme” from the Laplacian of surface pressure or vorticity around the core.
Seiler and Zwiers (2016) analyzed how explosive cyclones responded to climate change in the extratropical region of the NH. An objective-feature tracking algorithm was used to identify and track cyclones from 23 CMIP5 climate models for the recent past (1981–99) and future (2081–99). Explosive cyclones are projected to shift northwards by about 2.2° latitude on average over the Northern Pacific, with fewer and weaker events south of 45°N, and more frequent and stronger events north of this latitude.
Catto et al. (2019) reviewed the research progress on the structure, characteristics, dynamics, and impacts of explosive cyclones in the future and pointed out that multiple properties of the global climate system might influence the occurrence frequency, location, and intensity of explosive cyclones. Catto et al. (2019) had higher confidence in the future changes of three properties: (1) The atmospheric moisture content will increase due to the increase of temperature. (2) The lower-tropospheric meridional temperature gradient will decrease due to polar amplification in the NH in the winter. (3) The enhanced warming in the tropical upper troposphere and cooling in the high-latitude stratosphere will lead to an increased meridional temperature gradient in the vicinity of tropopause slope around 30°–40° latitude in the north and south. However, they had lower confidence in how these three factors would interact and contribute to future changes in explosive cyclones and the aggregated storm tracks. Finally, Catto et al. (2019) summarized the main features of explosive cyclones that were expected to change in the future.
All these features listed in Table 1, were summarized as follows:
Features 1 2 3 4 5 6 7 8 increased
upper-
tropospheric temperature
gradientdecreased lower-
tropospheric temperature
gradientincreased
static stabilityincreased
latent
heat releaseincrease in intensity
(extent)intensity
of the windsintensity
of the
central pressureprecipitation
and moisture transport
increasesConfidence High High High High High
(Low)Low Medium Low Table 1. Eight features associated with extratropical cyclones.
(1) Atmospheric baroclinicity and thereby storm development will be impacted by the increased upper-tropospheric temperature gradient (feature 1), decreased lower-tropospheric temperature gradient (feature 2) (over the NH only), and increased static stability (feature 3), as well as increased latent heat release (feature 4). These factors did not change monotonically with warming, and so there were still uncertainties around the precise impact.
(2) The precipitation intensity within explosive cyclones is expected to increase (feature 5), but there are mixed results in terms of how this feeds back onto the intensity of winds (feature 6) or the central pressure (feature 7).
(3) Due to the increase of precipitation and moisture transport, inland floods are projected to increase (feature 8), but there is a lack of catchment-specific information. Coastal floods from storm surge are likely to increase in the future, mainly associated with the sea level rising.
(4) Although the projections of wind strength are uncertain (feature 6), there are expected future increases in storm-related costs.
Features | ||||||||
1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | |
increased upper- tropospheric temperature gradient | decreased lower- tropospheric temperature gradient | increased static stability | increased latent heat release | increase in intensity (extent) | intensity of the winds | intensity of the central pressure | precipitation and moisture transport increases | |
Confidence | High | High | High | High | High (Low) | Low | Medium | Low |