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2024年4月18日 · greenhouse effect, a warming of Earth ’s surface and troposphere (the lowest layer of the atmosphere) caused by the presence of water vapour, carbon dioxide, methane, and certain other gases in the air. Of those gases, known as greenhouse gases, water vapour has the largest effect. The origins of the term greenhouse effect are unclear.
- The Editors of Encyclopaedia Britannica
3 天前 · Modern global warming is the result of an increase in magnitude of the so-called greenhouse effect, a warming of Earth’s surface and lower atmosphere caused by the presence of water vapour, carbon dioxide, methane, nitrous oxides, and other greenhouse gases. In 2014 the IPCC first reported that concentrations of carbon dioxide, methane, and ...
- Overview
- Types
- Frequency and disaster patterns
- Damage and deaths
- Disaster warning systems
natural disaster, any calamitous occurrence generated by the effects of natural, rather than human-driven, phenomena that produces great loss of human life or destruction of the natural environment, private property, or public infrastructure. A natural disaster may be caused by weather and climate events or by earthquakes, landslides, and other occ...
Weather- and climate-driven natural disasters include flooding caused by heavy rains associated with hurricanes and typhoons (tropical cyclones) and other intense storms; drought, famine, and wildfires brought on by heat waves and shifts in precipitation patterns; wind-generated devastation caused by tropical cyclones, tornadoes, derechos, and other windstorms; and damage and loss of life caused by blizzards and heavy snowfalls. Earth-driven natural disasters include large volcanic eruptions (which produce lava flows, explosions, toxic gas clouds, ash falls, and pyroclastic flows that damage populated areas) and strong earthquakes (which result from the sudden fracturing of Earth’s crust) powerful enough to damage or destroy built-up areas near their origin points.
Some phenomena that produce natural disasters may be caused by a combination of several different forces. For example, landslides (the movement of large masses of rock, debris, and soil downslope) may be caused by rains that saturate the soil on an unstable slope, or they may be triggered by earthquakes. In a similar manner, the buildup of snow on mountain slopes increases the risks of localized avalanches. Tsunamis, catastrophic ocean waves that can rise as high as 30 metres (about 100 feet) above normal sea level, are produced by submarine earthquakes, underwater or coastal landslides, volcanic eruptions, or meteor or comet impacts. The largest tsunamis are fast-moving waves that can travel across oceans to wreak havoc in coastal areas separated thousands of kilometres from one another.
Certain types of natural disasters are more likely to occur in specific geographic regions, and in some places these events occur with seasonal regularity, as in the spring tornado season in the United States or the summer-and-fall hurricane season in the Atlantic Ocean, Caribbean Sea, and the Gulf of Mexico. Earthquakes and volcanic eruptions are most frequent near tectonic plate boundaries, and an especially active boundary exists between the Indo-Australian and Eurasian plates.
The World Meteorological Organization (WMO)—a United Nations (UN) agency that monitors Earth’s land, water, and atmosphere—reported in 2021 that the number of natural disasters per decade showed a fivefold increase from 1979 to 2019, and data collected in the EM-DAT, an international disaster database maintained by the Center for Research on the Epidemiology of Disasters, Brussels, indicate that more than 300 disasters have been tallied each year since 1998. Though many natural disasters are neither preventable nor largely predictable, the WMO report notes that global warming—an increasingly human-driven phenomenon generated by the emission of greenhouse gases, specifically those released by the combustion of fossil fuels—is increasing the frequency of weather- and climate-related natural disasters, such as droughts, heat waves, increasingly intense hurricanes, and flooding due to sea-level rise. Warmer temperatures are causing more extreme weather events by delivering more precipitation to some areas—which may be unused to receiving heavy rains and snows, increasing flooding risk—while delivering less to other areas that rely on it, increasing drought risk. In addition, reliable sources of rainfall, such as the South Asian monsoon, on which agriculture of the Indian subcontinent has long depended, are becoming less predictable, and rain events have become more violent and dangerous, damaging crops and producing more intense flooding. This change has subjected some areas under the monsoon’s influence to extended drought conditions, whereas other areas receive too much rainfall, a pattern that scientists predict will worsen in the 21st century.
The costs of individual natural disasters frequently reach the tens of billions of dollars. Such costs may be associated with damage to crops, buildings, and infrastructure that occurs annually in areas prone to tropical cyclone activity or heavy seasonal rains, with some events, such as the Pakistan floods of 2022 and Hurricane Katrina (which struck the southern United States in 2005), costing more than $30 billion and $186 billion, respectively. Similarly, costs associated with earthquakes, which occur less regularly, can be high (such as China’s Sichuan earthquake of 2008 and Japan’s Kōbe earthquake of 1995, which incurred costs estimated at more than $86 billion and more than $100 billion, respectively).
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The number of deaths from natural disasters also varies by location and the intensity of the event; however, the overall trend points to a decline from several hundreds of thousands of deaths annually during the first half of the 20th century to roughly 45,000 deaths globally each year. The number of deaths also varies widely from year to year, with smaller natural disasters (or natural disasters occurring in areas far from human settlement) killing few and shockingly large disasters producing truly massive losses of life. Some of the most notable catastrophic disasters in history include the Indian Ocean tsunami of 2004 (which killed more than 225,000 people), the Tangshan earthquake of 1976 (which resulted in more than 242,000 deaths), the 2010 Haiti earthquake (which by some estimates may have killed at least 300,000 people), and China’s Shaanxi province earthquake of 1556 (which killed more than 800,000 people).
Advances in weather forecasting and advances in land-based seismic sensors and sensors placed aboard satellites, aircraft, and stationary buoys floating in the world’s oceans have led to the development of various kinds of early warning systems. In some cases, these systems are capable of predicting or accurately classifying the strength of the physical forces that generate natural disasters before they cause damage. The perhaps most widespread and best known of these systems are those used by national weather bureaus that classify, track, and predict various weather events and issue bulletins about storms and other weather and climate phenomena affecting their land areas and sea zones. National weather bureaus are often made up of a network of numerous local offices spread across a country that gauge local weather conditions several times per day. Data collected by these offices can be used to develop weather models that help to predict the strength of a storm, as well as its location, days in advance of its arrival in a local area.
In addition, specialized units within national governments—such as the China Earthquake Administration, the Japan Meteorological Agency, the United Kingdom’s Met Office, India’s National Center of Seismology, the U.S. National Oceanic and Atmospheric Administration, and the U.S. Geological Survey—monitor specific physical forces capable of causing the most damaging and deadly natural disasters (that is, earthquakes, tsunamis, droughts, flooding, and winds driven by tornadoes and tropical cyclones). Many of these organizations within specific countries cooperate with their counterparts in others or assist international organizations, such as the WMO and the International Tsunami Information Center, to issue warnings, develop international safety standards, and assess the risks associated with forces that affect several countries or the planet as a whole. Some early warning systems even look beyond Earth’s atmosphere; the near-Earth objects system operated by the European Space Agency and the Scout and Sentry impact hazard systems run by NASA in the United States are a few of several systems designed to detect, track, and predict the risk associated with asteroids, comets, and other extraterrestrial objects capable of striking Earth.
2 天前 · water pollution, the release of substances into subsurface groundwater or into lakes, streams, rivers, estuaries, and oceans to the point that the substances interfere with beneficial use of the water or with the natural functioning of ecosystems. In addition to the release of substances, such as chemicals, trash, or microorganisms, water ...
4 天前 · The Black Death is widely believed to have been the result of plague, caused by infection with the bacterium Yersinia pestis. Modern genetic analyses indicate that the strain of Y. pestis introduced during the Black Death is ancestral to all extant circulating Y. pestis strains known to cause disease in humans.
4 天前 · English language is a West Germanic language that originated in England and spread to many parts of the world. It is the dominant language of several countries and the most widely used lingua franca. Learn about its history, development, characteristics, and varieties from Britannica, the online encyclopedia that covers a wide range of topics and personalities.
5 天前 · Tornado, a small-diameter column of violently rotating air developed within a convective cloud and in contact with the ground. Tornadoes occur most often in association with thunderstorms during the spring and summer in the mid-latitudes of both the Northern and Southern Hemispheres. These whirling.
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