Earth’s lower atmosphere is becoming warmer and moister as a result of human-caused greenhouse gas emissions. This gives the potential for more energy for storms and certain extreme weather events. Consistent with theoretical expectations, the types of events most closely related to temperature, such as heatwaves and extremely hot days, are becoming more likely. Heavy rainfall and snowfall events (which increase the risk of flooding) are also generally becoming more frequent.
As Earth’s climate has warmed, more frequent and more intense weather events have both been observed around the world. Scientists typically identify these weather events as “extreme” if they are unlike 90% or 95% of similar weather events that happened before in the same region. Many factors contribute to any individual extreme weather event—including patterns of natural climate variability, such as El Niño and La Niña— making it challenging to attribute any particular extreme event to human-caused climate change. However, studies can show whether the warming climate made an event more severe or more likely to happen.
A warming climate can contribute to the intensity of heat waves by increasing the chances of very hot days and nights. Climate warming also increases evaporation on land, which can worsen drought and create conditions more prone to wildfire and a longer wildfire season. A warming atmosphere is also associated with heavier precipitation events (rain and snowstorms) through increases in the air’s capacity to hold moisture. El Niño events favour drought in many tropical and subtropical land areas, while La Niña events promote wetter conditions in many places. These short-term and regional variations are expected to become more extreme in a warming climate.
Earth’s warmer and moister atmosphere and warmer oceans make it likely that the strongest hurricanes will be more intense, produce more rainfall, affect new areas, and possibly be larger and longer-lived. This is supported by available observational evidence in the North Atlantic. In addition, sea level rise (see Question 14) increases the amount of seawater that is pushed on to shore during coastal storms, which, along with more rainfall produced by the storms, can result in more destructive storm surges and flooding. While global warming is likely making hurricanes more intense, the change in the number of hurricanes each year is quite uncertain. This remains a subject of ongoing research.
Some conditions favourable for strong thunderstorms that spawn tornadoes are expected to increase with warming, but uncertainty exists in other factors that affect tornado formation, such as changes in the vertical and horizontal variations of winds.
Page last updated: March 2020
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Climate change caused by the emission of greenhouse gases from human activities affects global temperature and precipitation. Records from the Intergovernmental Panel on Climate Change indicate that the global average temperature has increased by at least 0.4 degrees Celsius (0.72 degrees Fahrenheit) since the 1970s, and that by 2100, it could increase to around 4 degrees Celsius (7.2 degrees Fahrenheit) above preindustrial temperatures. While the global effects of climate change may seem too small to be noticed by people living around the world, we have already experienced the effects of climate change through severe weather events, including forest fires, hurricanes, droughts, heat waves, floods, and storms. Computer modelling of real data has shown that the frequency and intensity of these events are influenced by climate change.
There is a distinction that needs to be made when it comes to the relationship between climate change and extreme environmental events: Climate change has not been proven to directly cause individual extreme environmental events, but it has been shown to make these events more destructive, and likely happen more frequently,than they normally would be.
This drastic change is due to the increase in greenhouse gas emissions—primarily through the burning of fossil fuels for transportation, heat, and electricity—in the past 150 years. Greenhouse gases, such as carbon dioxide, methane, and nitrous oxide, trap heat within Earth’s atmosphere, making the planet warmer. A warmer atmosphere affects the water cycle because warmer air can hold more water vapor. In fact, the air’s capacity to hold water vapor increases by 7 percent with an increase in temperature of 1 degree Celsius (1.8 degrees Fahrenheit). This, along with warmer ocean temperatures, leads to heavier precipitation. Heavy precipitation can cause problems like flooding and landslides—where large amounts of soil or rock slide down a slope.
An increase in intense precipitation comes with an increase in intense dry periods as well. Essentially, climate change causes wet places to become wetter and dry places to become drier by altering large-scale atmospheric circulation patterns. Warmer temperatures on land lead to reduced snowpack, earlier snowmelt, and evaporation of water from freshwater bodies. Extreme heat can lead to more frequent, severe, and prolonged heat waves and droughts and can make forest fires worse. On top of that, wildfires are harder to put out when air temperature is high and soil moisture is low.
The number of heat waves, heavy rain events, and major hurricanes has increased in the United States. Hurricane Katrina of 2005 and Hurricane Sandy of 2012 are two of the most costly hurricanes in the history of the United States. The number of hurricanes that have occurred over recent years has not been linked to climate change, but their intensity has. The wind speed of tropical storms is increased by warmer sea-surface temperatures; by the end of the century, scientists predict maximum wind speed will increase by 2–11 percent. Coastal cities that are vulnerable to hurricanes will also be impacted by the sea level rise of around 0.3–1.2 meters (0.98–3.94 feet) in the next century, which will worsen coastal storms and flooding.
Without preparing for climate change–induced environmental hazards, an increasing number of people worldwide will lose their homes and be forced into poverty. An average of around 22.5 million people have been displaced per year by climate or weather-related events since 2008.
One way to prepare for extreme environmental events is by using current and past data and records to create computer models that show the frequency and intensity of these events. These models can also be used to predict when and where future events will occur and how destructive they will be. With this information, we can prepare for extreme weather events by warning people living in high-risk areas and sending disaster relief. The impact of climate change can also be observed in models by simulating the effects of different concentrations of greenhouse gases on variables, such as wind, rainfall, temperature, and air pressure.
Past models used to prove that there is a relationship between climate change and extreme environmental events were not always reliable. This was due to a lack of data as well as flaws in climate models at the time. However, climate models have become more reliable, and a new field of science has developed to determine how climate change directly impacts extreme weather events: extreme event attribution. Since 2004, scientists have published more than 170 studies on the role of human-induced climate change on 190 extreme weather events. Research has found that climate change has increased the risk of wildfires in the western United States, extreme rainfall in China, and drought in South Africa. Continuous research and improvement in the field of extreme event attribution may help us figure out more precisely how climate change impacts extreme weather events–and how we might change this course.