Extreme weather events
Extreme weather events refer to severe weather phenomena that have significant impacts on human life, property, and the environment. These events, including heavy precipitation, floods, droughts, heat waves, and storms, are becoming increasingly linked to global warming, which has led to rising global temperatures and altered weather patterns. This warming can intensify certain weather events, resulting in increased frequency and severity of floods in some regions, while paradoxically causing drought conditions in others.
Heat waves are also on the rise, contributing to an increased risk of wildfires, particularly in warmer climates. Additionally, tropical storms may become more intense due to higher ocean temperatures, although their overall frequency is complex and still under study. The implications of these extreme weather events are profound, affecting socioeconomic development, public health, and infrastructure, particularly impacting vulnerable communities. With trends indicating a rise in billion-dollar disasters, such as hurricanes and droughts, the urgency to understand and address these phenomena continues to grow. The interplay between climate change and extreme weather is a critical area of research as society seeks to mitigate the effects of these increasingly common occurrences.
Extreme weather events
Scientists have continued to study the effects of global warming upon both the intensity and the frequency of extreme weather events, particularly in terms of increased loss of life and property.
Background
Extreme weather events are weather systems that become abnormally severe and have high impacts on human life, property, and the environment. In the latter half of the twentieth century and into the twenty-first century, the global surface temperature experienced a rapid increase. Experts increasingly linked this rapid warming with significant changes in Earth’s weather patterns, affecting the frequency and intensity of extreme weather events.
Heavy Precipitation and Floods
One of the consequences of global warming that has been observed is the evaporation and transpiration of water vapor from oceans, rivers, lakes, and vegetated lands. Temperature is the main factor determining the moisture-holding capacity of air. The higher the temperature, the more moisture an can hold. Although global warming does not occur uniformly across the globe, experts have noted that the average temperature increase in the atmosphere has given rise to a corresponding increase of average humidity. More water content in the atmosphere increases the probability of heavy precipitation, which can lead to floods.
Another global warming–related factor that influences heavy precipitation and flooding is a convection-related increase in the severity of storms. In addition to increased temperatures, global warming has been found to involve a higher extension of Earth’s troposphere. Both of these processes can lead to more and stronger convection, which can in turn produce more violent convective storms and heavier precipitation.
Droughts
Since global warming is not uniform, a strong warming can occur in some parts of the world while other parts of the world cool. In response to such non-uniform conditions, different patterns of atmospheric circulation can be realized in different parts of the globe. As a result, in some areas air may be enriched by moisture, and in other areas the air may lose moisture, depending on the general atmospheric circulation patterns and moisture transport in each region. Therefore, while global warming can increase the intensity and frequency of heavy precipitation and floods in some locations, it can also increase the severity and frequency of drought conditions in others.
Heat Waves
Global warming increases air temperature in both average and extreme contexts. That is, it results in an increase not only in average temperature but also in daily, monthly, and yearly maximum temperatures. The increase in temperature extremes suggests an increase in the number of hot days as well. Therefore, global warming has already increased both the severity and frequency of heat waves. Such heat waves, along with drought, can increase the occurrence of wildfires.
Although wildfire is not a weather phenomenon, its occurrence is closely related to weather conditions. In particular, warm temperatures and low humidity are the two necessary conditions for wildfires. Because global warming can generate warm surface temperatures and frequent drought conditions, it has been found to increase the likelihood of wildfires such as the major fires reported in states such as California and Hawaii as well as other countries in the early 2020s.
Tropical Storms
One of the necessary conditions for tropical-storm formation is high sea surface temperature (SST). Tropical storms typically develop over the ocean when SSTs exceed 26 to 27 degrees Celsius. Furthermore, tropical storms derive energy from latent heat brought by water vapor evaporated from oceans. Higher SSTs promote greater evaporation of water into the atmosphere. This factor suggests that warmer climates can also produce more powerful hurricanes and typhoons. However, the question of whether global warming would cause an increase in storm frequency remained as the sample size of data was limited. A 2022 study indicated that the frequency of tropical storms had decreased by the early twenty-first century while often increasing in intensity. By 2023, experts had released findings that suggested intense hurricanes were developing and undergoing rapid intensification earlier than in the past.
Extratropical Cyclones
Unlike tropical storms, extratropical cyclones derive energy from a non-uniform temperature distribution, or a temperature contrast between locations in the northern and southern latitudes. In meteorology, such a condition is called a “temperature gradient.” Strong temperature gradients will generate unstable atmospheric conditions, which will initiate large-scale cyclones. These cyclones typically occur in the cool season, and they are enforced by upper-level jet streams and also characterized by surface fronts.
A general consensus exists that global warming can decrease temperature gradients and also decrease the intensity of jet streams. The combined effect of these changes tends to decrease the intensity and frequency of extratropical cyclones. However, some scientists argue that, because global warming tends to increase humidity, extratropical cyclones may gain extra energy from due to water vapor condensation.
Severe Thunderstorms and Tornadoes
Severe thunderstorms and tornadoes are convective-scale and microscale weather systems. They are different from extratropical cyclones, which are forced by large-scale temperature gradients. Thunderstorm development strongly depends on convection, which is influenced by surface radiative heating, convergence of surface flows, and topographic forcing. In a warmer climate, increases of global surface temperatures can provide favorable conditions for convection to occur. The number of both annual tornado sightings and annual tornado warning days increased over the second half of the twentieth century, but the number of the most severe tornadoes (F2-F5) exhibited a slight decrease. Into the early twenty-first century, studies continued to determine whether and to what extent global warming was impacting tornadoes, which remained particularly complex phenomena. By the 2020s, some experts were suggesting links between global warming and a shift in the areas where tornadoes commonly occurred.
Context
A 2007 report by the Intergovernmental Panel on Climate Change (IPCC) predicted that global warming would likely increase the number and frequency of extreme weather events. Despite the difficulty of attributing a particular weather event to climate change, a growing number of researchers sought to do just that. Between 2010 and 2016, the American Meteorological Society analyzed 131 scientific articles on selected extreme weather events and concluded in 2016 that human-caused climate change effects made an extreme weather event more likely or more severe in about 65 percent of cases. Increased extreme weather events are expected to generate profound impacts on global socioeconomic development. Such impacts include, among many other things, increased risks to human life and health, increased property and infrastructure losses, business income and tax revenue losses, increased cost and pressure on government’s disaster relief and mitigation resources, and increased costs of private insurance.
The year 2017 was the costliest year recorded up to that point in the United States for extreme weather events, totalling an estimated $306 billion in damage, of which three hurricanes accounted for $265 billion, wildfires $18 billion, and tornadoes, hail storms, severe storms, flooding, and a freezing event the remainder. Following 2017, the occurrence of billion-dollar extreme weather events only continued. According to the United States National Oceanic and Atmospheric Administration (NOAA), 2021 was the third costliest and second most prevalent for extreme weather events. Low-income members of society were disproportionately affected by those disasters. In 2022, the NOAA reported that this had been the eighth consecutive year in which the US had seen ten or more separate billion-dollar disaster events; the costliest events had included a major hurricane and an intense drought/heat wave.
This trend toward a higher number of extreme weather events continued as the 2020s wore on. Notably, in 2023, the US experienced twenty-eight billion-dollar weather disaster events. This was the highest number of individual billion-dollar disasters up to that point in the country's history. The most financially damaging disaster of that year was the summertime Southern and Midwestern drought and heat wave, which ruined crops, limited commerce on the Mississippi River, and caused $14.5 billion in damages. A drought and subsequent series of wildfires in Hawai'i in August of that year also caused billions in damages, as well as over a hundred deaths in the town of Lahaina. 2023 was also the hottest year on record in recorded history, and many parts of the US saw prolonged heat waves at different points of the year. This temperature record raised concerns that extreme weather trends would continue or perhaps even worsen in subsequent years.
Key Concepts
- cyclone: a storm system that rotates about a low pressure area
- drought: a long period of no or scarce precipitation
- extratropical cyclone: a cyclone originating and subsisting outside the tropics
- heat wave: an extended period of abnormally high temperatures
- hurricane: a cyclone originating in the tropics
- severe thunderstorms: mostly summer convective storms involving microscale rotating winds
- tornado: a narrowly focused, funnel-shaped violent windstorm
- wildfire: spontaneously ignited, naturally occurring fire
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