Recent hurricanes 20151/22/2024 įor the global hurricane analysis we choose to focus on the slightly shorter period from 1975 to 2010, as this is a reasonably homogeneous period of global satellite data going back to 1960 does not affect our conclusions. ![]() If greenhouse gases alone are considered then an extended period of nearly linear warming is justified, but anthropogenic impacts on the climate also arise from a range of other contributors that have counteracted the pure greenhouse gas warming until recently. This is quite different to a number of other studies that have assumed an essentially linear warming over the past 100 years or so. 2a indicate that consideration of the impact of anthropogenic climate change should be limited to the last four decades. 2004, 2012 Mann and Emanuel 2006 Thompson et al. This change has been attributed to reductions in emissions of sulfate aerosols, which counteracted the warming component due to greenhouse gases before 1960 (Meehl et al. After then, the anthropogenic simulations continue to track the observed global warming, but those with only natural forcing indicate a cooling trend back to nineteenth century temperature levels. The ensembles of model simulations with and without anthropogenic emissions closely track each other and the observed global surface temperature until around 1970. 1) indicates that the net anthropogenic climate forcing-including cooling as well as warming agents-was indistinguishable from natural variability until the mid-twentieth century (Meehl et al. However, comparison of global climate model simulations with and without anthropogenic forcing (Fig. This causes considerable problems with assessing the impact of climate change on severe weather events such as hurricanes (e.g. It is often assumed that anthropogenic climate change has occurred as a quasi-linear warming trend from around the turn of the twentieth century. 3 examines the recent hurricane signal, and discusses some of the consequences and our conclusions are in Sect. ![]() Here we investigate this apparent anomaly and find that there has been an increase in the proportion of intense hurricanes relative to all hurricanes, and that is strongly related to an Anthropogenic Climate Change Index (ACCI). Yet IPCC ( 2012) concluded that ‘There is low confidence in any observed long-term (i.e., 40 years or more) increases in tropical cyclone activity’, based largely on potential errors in the observed data. If we accept these two statements, then it logically follows that there should already be an observable increase in intense hurricanes. IPCC ( 2007) also concluded that the current ‘warming of the climate system is unequivocal’. The increases are substantial, approaching a doubling in frequency of Cat 4 and 5 hurricanes for each ☌ in global warming (Bender et al. 2010 Intergovernmental Panel on Climate Change-IPCC 2012) has concluded that it is likely that the frequency of intense hurricanes will increase with future anthropogenic climate change. ![]() Recent community consensus (Knutson et al. The analysis suggests that following an initial climate increase in intense hurricane proportions a saturation level will be reached beyond which any further global warming will have little effect. The observed increase in Category 4–5 hurricanes may not continue at the same rate with future global warming. This global signal is reproduced in all ocean basins. This has been balanced by a similar decrease in Category 1 and 2 hurricane proportions, leading to development of a distinctly bimodal intensity distribution, with the secondary maximum at Category 4 hurricanes. But a strong signal is found in proportions of both weaker and stronger hurricanes: the proportion of Category 4 and 5 hurricanes has increased at a rate of ~25–30 % per ☌ of global warming after accounting for analysis and observing system changes. We find no anthropogenic signal in annual global tropical cyclone or hurricane frequencies. This index indicates that the bulk of the current anthropogenic warming has occurred in the past four decades, which enables improved confidence in assessing hurricane changes as it removes many of the data issues from previous eras. ![]() The ACCI is defined as the difference between the means of ensembles of climate simulations with and without anthropogenic gases and aerosols. An Anthropogenic Climate Change Index (ACCI) is developed and used to investigate the potential global warming contribution to current tropical cyclone activity.
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