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How Are Severe Storms Effected by Climate Change Peer Reviewed Article

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1 Introduction

Extreme weather events tin exist defined as weather phenomena that are outside the climatology of a given location or area, representing astringent or unseasonable weather that occurs infrequently (Francis & Hengeveld, 1998). Though rare, farthermost weather condition tin dramatically affect society and have meaning short- and long-term repercussions, particularly in terms of loss of life and major impacts in the ecology, social, and economic sectors. For example, from 1990 to 2008, weather extremes accounted for, on boilerplate, nearly 35,000 deaths around the world annually (Goklany, 2009). In the Us lone, tornadoes and hurricanes together are responsible for billions of dollars in damage and over 100 fatalities annually (McNeill, 2012). There is a greater frequency of weather extremes in some years than others, such as in 2011, when 12 major weather disasters generated more than than United states$one billion in damage in the United States, coinciding with one of the deadliest tornado seasons in recorded history (Rice, 2011).

Changes in farthermost weather are critically of import drivers of climate change impacts, loss, and damages for many sectors of human order. Furthermore, studies of climate adaptation strategies require an understanding of the potential for changes in extreme atmospheric condition. As such, the response of farthermost weather events to anthropogenic climate change has received considerable attention in the scientific literature. Recent studies have linked a warming climate to irresolute frequency and/or severity of diverse atmospheric condition extremes, including astringent thunderstorms and tornadoes (Trapp et al., 2007), tropical cyclones (Stowasser, Wang, & Hamilton, 2007; Sugi, Murakami, & Yoshimura, 2009), heatwaves (Beniston, 2004), and wintertime storms at mid-latitudes (Lambert, 2004). The range of changes documented for different events in the literature is big and partly a outcome of climate models beingness unable to fully simulate or represent certain extreme weather phenomena, especially those that occur at sub-synoptic scales. This key uncertainty is also compounded by the presence of natural climate variability at multi-decadal time scales (Deser, Phillips, Bourdette, & Teng, 2010). Notwithstanding, uncertainties also emerge from the wide range of scenarios used to drive individual models, which hinders the ability to brand full general conclusions about anticipated changes in extreme atmospheric condition events associated with a given climate target. Electric current climate negotiations are focused on maintaining global temperatures at less than 2°C above pre-industrial levels, but currently the way in which weather extremes will be affected by this or higher levels of global temperature change is poorly understood (Intergovernmental Panel on Climate change, 2014).

The goal of this report is to explore the extent to which changes in farthermost atmospheric condition events can be quantified in a consequent manner as a function of global mean temperature change, based on existing climate modelling literature that has projected changes in extreme weather events in response to a range of greenhouse gas emissions scenarios. We nowadays here a meta-analysis of this body of literature to critically evaluate and statistically combine results from a range of climate modelling studies in gild to judge the response of selected conditions extremes to a given level of global mean temperature change. Based on the availability of literature, nosotros have focused our study on projected changes in tropical cyclones, tornadoes, heavy precipitation events, heatwaves, drought, tropical monsoons, and mid-latitude cyclones.

2 Methodology

a Literature Search and Scanning Stage

In the literature scanning process, we used a set of criteria to include or exclude articles from the written report. We considered merely recent (postal service-1990) peer-reviewed articles, collected from 29 unlike journals in the field of climate science. In total, we analyzed 127 journal manufactures for all the extreme weather events considered in this study. In general, we have opted to weight all studies as rather than attempt to evaluate the relative quality or robustness of individual results. It is probable that more recent studies are more reliable than older literature, and we have, therefore, endeavoured to focus our data collection on these more recent works (76% of the articles surveyed were published later on 2000). Nosotros besides excluded review articles (i.e., studies that simply reported results or findings from other literature), but nosotros sometimes used these manufactures as a means of retrieving the original research articles in order to gather additional data.

b Categories of Atmospheric condition Extremes

We included studies of extremes on a global scale as well every bit regional analyses of phenomena that accept pregnant implications for certain geographical areas. The extreme weather events that we discuss in this written report are summarized in Table i, with boosted details provided in Tabular array S1 (supplemental tables for this commodity tin be accessed at http://dx.doi.org/10.1080/07055900.2015.1077099). For a number of the weather events listed in Table ane, when direct estimates of changes were not available in the literature surveyed, we used proxies to aid in the assessment of how these extreme events may alter in response to future climate warming.

Table 1. Summary of weather extremes and analysis of sub-categories included.

For tropical cyclones, nosotros used their frequency to estimate changes in the total average number of cyclones (of all strengths) on a global calibration, as well equally in the individual sea basins of the northwest (NW) Pacific (0°–45°N, 100°Eastward–180°) and Atlantic (0°–45°N, xc°Westward–0°). We similarly analyzed Saffir-Simpson categories iv and 5 tropical systems merely (i.east., cyclones with surface wind speeds of at least 50 m due south−one) on a basin and global scale. In addition, we examined changes in tropical cyclone "intensity" based on changes in the hateful surface and about-surface maximum air current speeds (metres per second) of cyclones (of all strengths) achieved during the lifetime of tropical cyclones.

We used estimates of global precipitation (millimetres per twenty-four hours) to represent changes in atmospheric precipitation (of all types) and isolated estimates of global precipitable water and convective precipitation as proxies for potential changes in heavy precipitation events. Precipitable water is defined every bit the amount of wet within a given column of air that can be condensed into liquid h2o. The measures of convective precipitation that we assessed generally come up from model parametrizations of the atmospheric precipitation associated with deep convective systems, which represent systems that take a big vertical depth within the troposphere, typically extending from the surface to above the 500 hPa geopotential height level. Although non responsible for all types of farthermost precipitation, these deep convective systems practice commonly manifest every bit thunderstorms and heavy rainfall events, particularly in tropical regions and in the mid-latitudes during spring and summer.

Regarding the South Asian monsoon, we used boundary-layer zonal winds and warm flavor rainfall to gauge changes in the force of the monsoon. The strong correlations between rainfall onset/intensity and the strength of the zonal wind in the Southward Asian monsoon region (e.grand., Qian & Zhu, 2002), too as the zonal wind'southward coupling to the El Niño–Southern Oscillation (ENSO) in the same region (Webster & Yang, 1992), brand this a particularly useful metric of monsoonal strength. In this study, we define zonal winds as wind speeds (metres per second) occurring within the boundary layer (i.east., from the surface to the 850 hPa pressure level (about 1.5 km higher up the surface)), whereas warm season rainfall (millimetres per twenty-four hours) refers to changes in rainfall occurring from June through September.

We have also included an analysis of individual mid-latitude cyclonic storms because they drive many other weather extremes, including severe thunderstorms, strong winds, tornadoes, and major snow events. We used annual mid-latitude cyclone frequency as a metric for the total number of mid-latitude cyclones of all strengths throughout the year in the northern hemisphere (NH) and southern hemisphere (SH) that occur between latitudes xxx°–55°N and 30°–55°S. Absurd season mid-latitude cyclones in the NH and SH refer to changes in the total number of cyclones that have place during the November to March and May to September periods, respectively. Intense absurd season cyclones are distinguished in this study as cyclones that attain central surface pressures of 970–980 hPa or lower.

In improver to regional and global precipitation patterns, nosotros besides surveyed literature pertaining to changes in North American and European soil moisture, which tin suggest irresolute drought and heatwave conditions over these regions. Soil moisture is measured within the uppermost ten cm of soil. Similarly, we used the number of days with temperatures of 30°C or greater in Europe to estimate changes in European heatwaves in a warmer climate.

With respect to astringent convective events, certain alphabetize parameters, such equally vertical air current shear and the number of severe thunderstorm development days (NDSEV), are useful indicators for severe thunderstorms and tornadoes. In this written report, nosotros define US vertical wind shear as changes in current of air speed and management occurring above the boundary layer (from the 850 hPa to 200 hPa force per unit area levels) over the contiguous United States; NDSEV is besides measured over the contiguous United States and is the product of convective available potential energy (CAPE) and vertical wind shear (wind shear occurring from the surface to half dozen km above the surface). Both US NDSEV and vertical wind shear quantities are representative of the spring and summertime, from March to August.

We too included ENSO in this report considering it is one of the well-nigh influential modulators of both global climate and extreme weather events. To analyze changes in ENSO, nosotros examined ENSO aamplitude and period by focusing on projected changes in sea surface temperatures (SSTs) in the Niño 3.4 region (five°North–5°S and 170°–120°West) and the Niño 3 region (v°Due north-5°S and 90°–150°W) because these regions are ordinarily used to determine the birth of an El Niño or La Niña outcome based on persisting SST anomalies. The ENSO amplitude typically refers to either the intensity of cool ENSO phases (La Niña) or warm ENSO phases (El Niño). The ENSO period, by dissimilarity, is related to the frequency of the ENSO cycle (ENSO-cool, ENSO-warm, and neutral phase frequency).

c Information Collection and Estimation

From each written report that we surveyed, we recorded the authors' judge of changes in the weather extremes and identified their methods for applying greenhouse gas concentration scenarios. The majority of the articles we surveyed used coupled atmosphere–body of water general circulation models, driven by either transiently increasing greenhouse gas concentration scenarios or by constant elevated concentrations. Transient greenhouse gas scenarios included the Representative Concentration Pathways (RCP), the Intergovernmental Panel on Climate Modify (IPCC) Special Report on Emissions Scenarios (SRES), and the IS92 scenario from the IPCC Second Assessment Report. Constant COii scenarios included a doubling, tripling, quadrupling, or even a six-fold increase in atmospheric COii relative to pre-industrial values, 1961–1990 climatology, or specified present-twenty-four hour period concentrations. Details of the model and scenario used in each report are provided in Table S2.

As a variety of different greenhouse gas forcing scenarios are applied in these studies, we used the global mean temperature alter of each model simulation as the baseline for our multi-study intercomparison in guild to summate the total change in extreme conditions events per caste Celsius of global warming. In all cases, we used a value of temperature alter relative to the reference period reported in each study (e.g., pre-industrial or present-mean solar day temperatures). When the authors of an article did non study a value for the false global mean temperature change, nosotros attempted to contact them straight to obtain this measure out. In those cases in which studies reported results of previously published model simulations included as function of the intermodel comparisons, we were able to retrieve the global mean temperature increase for each simulation from published reports, such every bit the IPCC assessments. When information technology was not possible to gauge the global hateful temperature change, nosotros did not include the article in our meta-assay.

Many of the studies nosotros examined included data about regional (rather than global) temperature alter. When nearly-surface air temperature modify was reported for a detail region, we estimated the respective global mean temperature change using the model-average spatial pattern of temperature change per unit of measurement global hateful warming from Solomon et al. (2011). When studies reported global SSTs, rather than air temperature change, we used the ratio of SST to global mean temperature change from HadCRUT (Climate Research Unit, 2013) to estimate the corresponding air temperature change. In those situations when only a regional SST change was provided, we causeless the about-surface air temperature change to be equivalent to the reported SST change and used the upscaling procedure described above to convert from a regional to a global temperature change.

d Statistical Analysis

The information collection procedure outlined in Department 2c yielded estimates of the change in extreme weather events per degree Celsius of global warming. Each estimate represents the output from a given climate model or group of models and was treated every bit a unmarried data bespeak in the subsequent statistical analysis. As a compromise, to preserve data variety and sample size, these data points were treated every bit statistically independent, despite sometimes existence fatigued from different versions of the same models (e.1000., with different atmospheric resolutions). Furthermore, the statistical independence of each estimate disregards the college-level structural dependencies that are known to exist between models developed by different centres (Knutti, Furrer, Tebaldi, Cermak, & Meehl, 2010). However, when the same model was used to simulate the response of a given weather extreme to different emissions scenarios, these information points were not treated as independent but were instead averaged to gauge the mean response in this particular model. When studies used model means to document their results, these data points were included in the sample (despite potential overlap with individual model results), every bit long as the model means independent at least one non-replicated model for a given extreme weather variable.

Later establishing a set of data points for each farthermost atmospheric condition event, nosotros then tested each group of data to determine whether the mean change was significantly different from zero. Nosotros used a ane-sample t-test for cases in which the data appeared to be normally distributed upon inspection of normal quantile-quantile diagnostic plots. When there were insufficient data points to assess the normalcy of the data or when the information deviated notably from a normal distribution, nosotros used the not-parametric Wilcoxon Rank Sum examination. Non-parametric tests are especially advisable for pocket-size sample sizes when the distribution of the data is unknown; nonetheless, statistical results that are based on simply a few studies are likely less robust than those that take more than data points available.

In the post-obit sections, we present frequency density plots, which represent smoothed and normalized versions of data histograms to facilitate the plotting of several sets of related information points on a simple figure console. These figures, therefore, bear witness those weather events that are expected to increase or decrease significantly as a function of global mean temperature increases. In addition, nosotros have summarized the results for all extreme weather variables in tables in the following sections, in which we have indicated the number of data points, the mean, the standard deviation, the statistical test used, and the resulting p-value. When results were statistically significant, we noted the level of significance by annotating the direction of alter (increase or decrease). We highlighted levels of significance by using asterisks, where *, **, *** denote statistical significance at or inside the 0.one, 0.05, and 0.01 levels, respectively.

3 Results and word

a Global and Regional Tropical Cyclones

Nosotros institute that global tropical whirlwind frequency is expected to decrease with increasing global warming, with an average decrease found here of 6.8% per caste Celsius of global warming (Fig. 1a). This consequence is statistically meaning (p= 0.02), equally shown in Tabular array ii. On a global scale, we did non find a significant change in the overall frequency of the most intense storms (categories iv and 5 only) nor an increase in the overall intensity of all storms.

Fig. 1 Global (blackness curve), NW Pacific (red curve), and Atlantic (bluish curve) tropical cyclone (TC) changes per caste Celsius of global warming. Frequency density plots brandish percent changes per degree Celsius for (a) all TC frequencies, (b) the frequency of category four and 5 storms, and (c) the overall TC intensity.

Table 2. Results for global and regional tropical cyclone patterns.

Despite the lack of a global trend, both the NW Pacific and Atlantic basins showed statistically meaning changes in tropical cyclone intensity. The overall intensity of all tropical cyclones (defined based on mean maximum surface wind speed) is expected to increment significantly by 3.7% per degree Celsius (p< 0.01) for the NW Pacific and by 3.5% (p =0.02) per degree Celsius for the Atlantic (Fig. 1c). In improver, we found that the frequency of the most intense storms in the NW Pacific basin is expected to increase by xviii.7% (p< 0.01; Fig. 1b), though this alter was non statistically significant for the Atlantic basin.

The observational record shows that, since the 1950s, there has not been a large trend in the frequency of tropical cyclones that fabricated landfall, though there is some evidence of an increase in the intensity of these since the mid-1990s (Weinkle, Maue, & Pielke, 2012). Our results suggest that futurity trends are likely to reveal a decrease in global tropical cyclone frequency in a warmer climate but that the storms that practice occur could potentially become more severe, as shown by an increase in storm intensity in both the NW Pacific and Atlantic basins. This tropical cyclone intensification could imply either a general increment in the intensity of all storms or a larger percentage of storms attaining higher category strength, particularly in the instance of the NW Pacific basin. These findings are consistent with Knutson et al. (2010), who projected a ii–xi% increase in global tropical cyclone intensity and a half-dozen–34% decrease in the frequency of global tropical cyclones by 2100. A subtract in global (and regional) tropical whirlwind frequency could be related to enhanced upper-tropospheric warming and greater vertical air current shear in some basins (i.eastward., SH; Knutson et al. (2010) and the Atlantic; Yip and Yau (2012)). Notwithstanding, our results projecting increased severity of tropical cyclones, with a correspondingly college percentage of college-category storms, could be driven by an increase in the potency of dynamical features, such as SST warming and purlieus-layer moistening (Gualdi, Scoccimarro, & Navarra, 2008; Knutson, Tuleya, & Kurihara, 1998).

b Global Precipitation

We establish a significant increase in global precipitation (Fig. two and Table three). The studies nosotros surveyed reported increases of up to v% per degree Celsius of global warming, with a statistically significant mean increment of 1.iv% (p< 0.01). For both the corporeality of global precipitable water and the amount of convective precipitation, we also found pregnant increases of 7.v% (p< 0.01) and half-dozen.6% (p= 0.06) per caste Celsius of global warming, respectively (Fig. 2 and Table 3).

Fig. 2 Global precipitation, global precipitable h2o, and global convective rainfall changes. Frequency density plots show the distribution of per centum changes per caste Celsius of global warming for global precipitation (black curve), global precipitable water (scarlet curve), and global convective rainfall (blue curve).

Table three. Results for selected global atmospheric precipitation variables.

This robust increase in global precipitable water is consequent with the increase in atmospheric moisture content expected from the Clausius-Clapeyron relationship (Boer, 1993; Bosilovich, Schubert, & Walker, 2005; Held & Soden, 2006). This relationship describes the temperature dependence of the saturation vapour pressure and shows that for every change of one kelvin there is a corresponding seven% increase in atmospheric h2o property chapters (Radermacher & Tomassini, 2012). This may, in turn, provide more buoyant energy for the germination of deep convective systems in a warmer climate. This is consistent with a pregnant increase in global convective rainfall reported here and is too reflected in historical observations of atmospheric moisture, which has increased from 1973 to 1995 (Trenberth, Fasullo, & Smith, 2005). Observed global precipitation has also increased over the final century; in particular, Kumar, Merwade, Kinter, and Niyogi (2013) reported an average global increment of 0.78 mm per decade during the 1930–2004 period.

c South Asian Monsoon

Our findings indicate that the South Asian monsoonal purlieus-layer zonal winds may weaken significantly with global warming (Fig. 3a and Table iv), with an average subtract of 0.29 m southward−1 per degree Celsius of global warming (p= 0.04). By dissimilarity, we constitute that average summertime rainfall in the region is expected to increment by 3.6% per degree Celsius of global warming (Fig. 3b and Table 4), a result which is highly statistically significant (p< 0.01).

Fig. 3 South Asian monsoon pattern changes. Frequency density plots display changes per degree Celsius of global warming for (a) absolute changes (m south−1) in Southward Asian monsoonal zonal winds and (b) percentage changes in the Due south Asian warm flavor rainfall.

Tabular array 4. Results for South Asian monsoon patterns.

The increases in South Asian warm season monsoonal rainfall constitute hither in response to increasing temperatures are consistent with the articulate trend towards enhanced global precipitation. The significant increase in global precipitable h2o and global convective rainfall, equally discussed in the previous section, is reflected in the regional warm season monsoon. However, our results as well show a significant waning of the mean warm flavor zonal wind flow, which suggests a general weakening of the monsoonal circulation. Various climatic factors may, therefore, be playing a office in offseting this weakened monsoonal apportionment with ascent global mean temperatures, leading to an overall increase in monsoonal precipitation, despite weaker zonal winds. For instance, increased wet availability, reduced Eurasian snowfall depth and/or coverage associated with enhanced Eurasian warming during the NH winter and stronger surface convergence generated by enhanced state–ocean temperature and pressure gradients between the Indian subcontinent and the Indian Bounding main (e.g., Lal, Meehl, & Arblaster, 2000; Meehl & Washington, 1993) may lead to a net increase in the South Asian monsoonal precipitation through a lengthening of the monsoon season (Stocker et al., 2013). It is as well possible that a weakening of monsoonal winds could be related to a weaker coupling of monsoonal circulations with ENSO in a warmer climate (e.g., Ashrit, Kumar, & Kumar, 2001; Kripalani, Oh, Kulkarni, Sabade, & Chaudhari, 2007).

d Mid-latitude Cyclones

The boilerplate annual total number of mid-latitude storms is projected to subtract by an boilerplate of i% per degree Celsius of global warming in the NH (p= 0.04) (Fig. 4 and Table 5). A similar trend is reported in the literature for annual SH mid-latitude storms, though this change was non statistically significant in our analysis because of the small sample size and larger spread of the reported results. When considering only these storms, our findings suggest that both hemispheres will run across a significant decrease in the overall frequency of cool season storms (NH: p< 0.01; SH: p= 0.03). By dissimilarity, the total number of intense cool season cyclones in the NH and SH shows an increase with higher global temperatures, with particularly pregnant increases in the SH (NH: p= 0.08; SH: p< 0.01).

Fig. 4 Northern hemisphere (NH; black curve) and southern hemisphere (SH; red curve) mid-latitude whirlwind design changes. Frequency density plots highlight changes per caste Celsius for (a) annual cyclone frequency (%), (b) hemispheric frequency of cool season cyclones (accented modify), and (c) hemispheric frequency of intense cool flavor cyclones (absolute change).

Table 5. Results for hemispheric mid-latitude cyclone patterns.

In an analysis of contempo observational trends, Wang et al. (2013) showed that the number of annual extra-tropical systems has declined slightly in the NH merely has increased in the SH over the 1871–2010 menses. In improver, Wang et al. (2013) suggested that the frequency of intense baroclinic cyclones has increased for both the NH and SH, with the greatest change occurring in the SH. This ascertainment is, thus, consistent with the projected increase in intense cyclones shown here. The overall decrease in cool-season cyclones that we report here may be related to a projected reduction in baroclinicity (i.e., horizontal temperature gradient) at mid-latitudes (eastward.one thousand., Catto, Shaffrey, & Hodges, 2011; Geng & Sugi, 2003). Reduced meridional temperature gradients could, in plow, be linked to reduced winter sea ice and snowfall coverage in a warmer climate. With a weakened latitudinal temperature gradient, vorticity advection becomes less prominent, resulting in less favourable atmospheric condition for the synoptic-scale vertical ascent required for the development of mid-latitude cyclones (Geng & Sugi, 2003). Furthermore, weakened mid-breadth baroclinicity could be the result of a poleward-shifted storm track, suggesting that the increased frequency of intense cyclones could be displaced toward higher latitudes (eastward.g., Bengtsson, Hodges, & Roeckner, 2006; Fyfe, 2003; Mizuta, Matsueda, Endo, & Yukimoto, 2011). Some other contributing factor to the failing frequency of mid-latitude cyclones is the reduction in global tropical cyclones, which are important sources for mid-latitude cyclones following extratropical transition.

Despite the subtract in the total number of mid-latitude cyclones, the projected increment in the intensity of these systems could yield more pregnant precipitation events and stronger force per unit area gradient winds (Reed, 1990; Watterson, 2006). More than intense cool flavor storms as well coincide with greater moisture and precipitable water availability discussed previously; in item, Sinclair and Watterson (1999) and Geng and Sugi (2003) showed that increased water vapour and humidity in a warmer climate favours the development of more intense mid-breadth cyclones considering of the latent estrus enhancement of quasi-geostrophic vertical ascent on synoptic scales. The significant increase in the number of SH intense storms during the austral winter could also exist related to the poleward displacement of the storm rail, which allows for easier accessibility to cold Antarctic air masses, thereby increasing the available potential energy for storms (Bengtsson et al., 2006).

e Drought and Heatwaves

Our analysis of European and N American soil moisture (Fig. 5a) shows a general subtract in soil moisture in a warmer climate for both regions, with an average decline of seven.4% per caste Celsius of global warming in Europe (p= 0.01) and seven.2% per caste Celsius in North America (p= 0.02) (Fig. 5a and Table 6). With respect to the frequency of heatwave weather in Europe (the number of days with maximum temperatures of 30°C or more), we institute a large increment of about 109.v% per degree Celsius of global warming, which is, yet, only weakly significant (p= 0.06) because of the very pocket-sized sample size. This result should be treated with caution, however, because it is based on only a few private studies.

Fig. five Regional soil moisture changes and changes in the number of days in Europe with maximum temperatures ≥xxx°C. Frequency density plots brandish the distribution for percentage changes in soil moisture per degree Celsius of global warming for (a) Europe (black curve) and Due north America (red bend) and (b) days with temperatures thirty°C or greater in Europe.

Table vi. Results for European and Northward American soil moisture changes and days in Europe with maximum temperatures ≥thirty°C.

In the observational record, it has been found that global aridity increased from 1950 to 2010, mostly because of drying occurring over southeast Asia, eastern Commonwealth of australia, southern Europe, and over most of the African continent (Dai, 2011, 2013). This global increase in drought areas is likely related to ongoing warming that has occurred since the 1980s, resulting in an 8% increment in the areas nether drought over the first decade of this century (Dai, 2013). Observational data used by Feng and Fu (2013) showed further that drylands have increased in coverage by approximately 4% since the 1950s, with models consistently underestimating the actual extent of dryland expansion.

The significant subtract in both European and Due north American soil moisture shown hither is occurring in the context of an overall increase in global precipitation, suggesting an increase in warm season evapotranspiration in these regions equally an important factor (Intergovernmental Panel on Climate Modify, 2014; Sherwood & Fu, 2014). Previous research has also shown that decreased summer soil moisture, specially at mid-latitudes, may exist associated with an increment in the rain–snow ratio during libation seasons and earlier snowmelt in the spring (Mueller & Seneviratne, 2012; Sheffield & Forest, 2008). A meaning decline in soil moisture too reflects a decrease in cool season mid-breadth cyclones. With more storms following a poleward-shifted trajectory, this would imply a decreased likelihood of heavy snowfall events in the mid-latitudes considering of increased boundary-layer temperatures in the troposphere. The result would exist less frozen winter precipitation over the mid-latitudes of the NH, including Europe and North America, which is detrimental to the soil moisture recharge process at the end of the wintertime flavour. As a result, warm-season drought conditions could become more prevalent because of reduced soil moisture.

Other research has institute that in that location is a potential for heatwaves to increase in frequency and severity over both Europe and North America (Meehl & Tebaldi, 2004), consequent with our synthesis of modelling studies for days of 30°C or greater in Europe. According to historical datasets of daily high temperatures for the contiguous United States from the 1950s to 2000s, the number of record daily highs has increased since the 1970s, with unusually hot summertime days and warmer summer overnight lows becoming more common (EPA, 2013). With respect to Europe, Schar et al. (2004) found that future temperature and precipitation patterns for the 2071–2090 period more than oftentimes resemble the anomalously hot European summer of 2003, likely because of increased soil moisture depletion and convection inhibition. Our meta-analysis indicating a pregnant increase in the number of days with temperatures reaching xxx°C or higher across the European continent is also consequent with projections of lower soil moisture content over the region, given that decreased soil moisture can both amplify already hot conditions (due to a decrease in evaporative cooling), equally well as be exacerbated past high temperatures (due to higher potential evaporation) (Hirschi et al., 2011; Schar et al., 2004).

f Indices Related to Severe Thunderstorms and Tornado Development

Although severe thunderstorms and tornadoes occur well below the calibration of nigh climate models, synoptic-scale diagnostic indices, such as vertical wind shear (required for the germination of tornadic storms) and the frequency of days with synoptic conditions favourable for astringent thunderstorm development, can be used equally wide indicators of the potential for severe convection. The studies sampled here indicate that vertical wind shear, measured between 850 and 200 hPa geopotential heights, is projected to decrease over the contiguous United States with global warming. In particular, models projection decreases of up to 5% (Fig. 6a) and an average decrease of one.seven% per degree Celsius of warming (p= 0.ten). Another useful metric derived from model output variables is the NDSEV, defined as the product of vertical current of air shear between the surface and 6 km elevation, and CAPE in the troposphere (Trapp et al., 2007). From our survey, we plant that NDSEV increases with college global temperatures (Fig. 6b and Tabular array 7) by 7% per degree Celsius (p= 0.04).

Fig. 6 North American vertical air current shear and severe thunderstorm development day (NDSEV) changes. Frequency density plots highlight the distribution of percentage changes per degree Celsius of global warming in terms of (a) vertical wind shear and (b) severe thunderstorm development days.

Table 7. Results for selected indices related to severe thunderstorm and tornado development.

Decadal tornado counts since the early twentieth century advise that tornado frequency, including the number of intense tornadoes, has increased sharply in the United states of america (NOAA, 2013). However, some of this drastic alter may be related to increases in densely populated areas, storm spotters, weather watchers, storm chasers, and advice systems (warning systems formally introduced in the 1970s). A closer inspection of recent decades shows that there has been no significant change in tornado frequency, although, since the 1970s, there has been an observed increase in the variability of the annual and monthly occurrence of tornadoes, and there have been changes in the onset time of the tornado flavor (Brooks, Carbin, & Marsh, 2014). In addition, a model estimating changes in tornado intensity from records of path length and width indicates a slight increase in frequency of the almost intense tornadoes with time (Elsner, Elsner, & Jagger, 2014a). Furthermore, accounting for potential reporting biases, Elsner, Jagger, and Elsner (2014b) showed that both tornado density and the number of days with eight or more tornadoes (a tornado outbreak) are increasing robustly with time. This trend is generally reflected in our synthesis of the literature, which suggests an increase in (NDSEV) days conducive to severe thunderstorm outbreaks.

Although only addressed by a few (merely increasing) number of studies, our synthesis of available literature suggests that astringent thunderstorm frequency (as measured by NDSEV) could also increment in response to global warming, despite a general decrease in mid-latitude baroclinicity and associated vertical wind shear. An increment in astringent convection would be consistent with increased precipitable water in the atmosphere because moistening of the lower troposphere could increase Cape in a warmer climate, thus providing for stronger updrafts in thunderstorms. Indeed, the robustly higher Cape and greater surface moisture in model projections for North America are key factors increasing severe convection potential in the hereafter (Diffenbaugh, Scherer, & Trapp, 2013; Paquin, de Elía, & Frigon, 2014).

The combination of increased CAPE and weaker shear (such as in Trapp et al. (2007, 2009)) could pb to more thunderstorms causing wink floods and producing stronger downdrafts because the effect of water loading is enhanced while storms exhibit slower propagation speeds. On the other manus, Paquin et al. (2014) showed that projected decreases in vertical shear over the 20-first century are very slight for virtually regions of North America, with more significant decreases only seen in Arctic regions along the polar jet. Further, Diffenbaugh et al. (2013) showed that the climatologically lower vertical wind shear projected for the eastern continental U.s.a. in the Coupled Model Intercomparison Project, stage 5 (CMIP5) occurs mostly during days with depression CAPE, while days with severe thunderstorms (robustly increasing with global warming) are still characterized past both a loftier-Cape and high-shear environment. Therefore, supercell development that occurs under high-shear and low-CAPE weather may become less common in the futurity, although weather condition favourable for larger outbreaks are withal likely to be characterized by high vertical wind shear and, thus, not necessarily increasingly dominated past linear convection (Diffenbaugh et al., 2013).

Another important consideration for future astringent thunderstorm distribution is proximity to moisture source regions. While global precipitable water increases, decreases in Northward American soil moisture suggests a greater dependence on moisture advection (rather than local sources) to fuel severe convection. Limited surface moisture in some regions could also lead to an increase in elevated and low-precipitation variety supercells, which are capable of producing stronger outflow and large hail because of the enhanced effect of evaporative cooling in a drier boundary layer. Moisture availability is a particularly important consideration, given the projected poleward shift in baroclinicity with global warming (e.g., Mizuta et al., 2011), leading to potentially more favourable tornadic environments located in northern regions of the United States and southern Canada.

1000 El Niño–Southern Oscillation (ENSO)

According to the literature surveyed, the amplitude of ENSO (representing the overall strength of individual El Niño and La Niña events) is not expected to modify significantly with global warming (Fig. 7 and Table 8). All the same, we did find a significant subtract in the period of the ENSO bicycle by an boilerplate of 3.4% per caste Celsius of global warming (p= 0.01; Fig. 7 and Table 8).

Fig. 7 ENSO amplitude and menses changes. The frequency density plot shows the distribution of pct changes in ENSO amplitude (black curve) and period (scarlet curve) per degree Celsius of global warming.

Table 8. Results for ENSO patterns.

A written report that used tree-band information from the American Southwest to reconstruct an 1100-year history of ENSO cycles revealed a fifty- to 90-year bicycle of El Niño intensity and showed that the variance betwixt El Niño and La Niña events becomes more pronounced when the groundwork temperature is warmer and smaller during libation periods (Li et al., 2011). This piece of work suggests that future warming could enhance ENSO variability, which would be consequent with our finding of more frequent (if not stronger) El Niño and La Niña events. This decrease in the ENSO menstruation may also exist associated with a larger meridional temperature gradient northward and south of the equator in the Pacific, which would favour a more rapid fluctuation in the depth of the thermocline across the Pacific, as suggested by Collins (2000a). The changes in the ENSO catamenia may also be driven by an enhancement of the equatorial wave speed caused by increased stratification associated with greater bounding main surface warming (Chen, Kimoto, & Takahashi, 2005; Merryfield, 2006).

These changes in ENSO could have of import implications for the future occurrence of many of the farthermost weather events that nosotros accept discussed previously, including tropical cyclone germination (Saunders, Chandler, Merchant, & Roberts, 2000), South Asian monsoonal winds (Ashrit et al., 2001; Kripalani et al., 2007), and the number of North American severe conditions days (Marzban & Schaeffer, 2001). However, it is worth noting that ENSO projections remain a particularly uncertain aspect of future extreme weather projections, with model projections showing a broad range of responses to global warming (Timmermann, Jin, & Collins, 2004). There is as well incertitude associated with the response of the overall tropical Pacific east–west SST pattern to increasing global temperatures (Collins, 2000a), which may exist related to the relatively rudimentary way that subgrid-scale ENSO processes are represented in global climate models (Collins, 2000b).

5 Conclusions

In this study, we performed a meta-assay of the literature pertaining to model projections of changes in extreme weather events in an endeavour to better quantify how such events may respond to global warming. By evaluating all weather events consistently every bit a role of global mean temperature change, we have shown that increasing greenhouse gas concentrations in the atmosphere could influence near all types of extreme conditions events for which at that place were enough contained estimates in the literature to be included in our report.

These results provide important data for researchers in the fields of climate impacts and accommodation, where extreme atmospheric condition events are a highly relevant machinery by which global warming will affect human and environmental systems. Indeed, changes in the frequency and intensity of extreme atmospheric condition will probable be one of the most tangible and potentially damaging direct impacts of global warming for humanity. Drought and heatwaves may lead to considerable losses in the agricultural sector (virtually notably at mid-latitudes), where the frequency of precipitation events could decrease because of decreases in the frequency of cyclonic storms. The combination of unsaturated soil surfaces and heavy rainfall events could also lead to more localized flooding, especially in South asia, where warm flavor monsoonal rains are expected to increase in a warmer climate. Pregnant increases in tropical cyclone intensity with warmer global temperatures may lead to a higher incidence of coastal inundation and enhanced property damage associated with landfalling storms. More severe thunderstorm development days could as well pb to more frequent severe convective outbreaks and costlier severe weather seasons for portions of the United states from damage and casualties related to tornadoes, strong winds, hail, and wink floods during spring and summer. Many of these impacts may exist exacerbated by increases in the frequency of El Niño and La Niña events and their influence on the frequency and severity of extreme weather at the global scale. Additionally, the increased availability of atmospheric moisture is central to the intensification of multiple farthermost weather phenomena, notably tropical cyclones, mid-latitude cyclones, severe thunderstorms, and tornadoes.

With global temperatures projected to continue to ascension throughout the xx-first century, it is imperative to implement adaptation measures that would reduce the societal impacts from more than extreme weather condition events in a hereafter climate. In addition, our study suggests that more research is needed to ameliorate forecast the response of certain conditions events to global warming, particularly those that occur at sub-synoptic scales, such every bit severe thunderstorms and tornadoes. Furthermore, many uncertainties remain in our understanding of ENSO behaviour in a warming climate because of an incomplete representation in climate models of the primal concrete processes that drive ENSO cycles. It is critical that we increment our understanding of the fashion in which ENSO will respond to global warming to improve both brusk- and long-term predictability of farthermost weather condition events that can be concretely linked to this key design of climate variability.

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Source: https://www.tandfonline.com/doi/full/10.1080/07055900.2015.1077099

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