They consider extreme weather events to be those that produce unusually high or low levels of rain or snow, temperature, wind, or other effects. Global warming can contribute to the intensity of heat waves by increasing the chances of very hot days and nights.
Warming air also boosts evaporation, which can worsen drought. More drought creates dry fields and forests that are prone to catching fire, and increasing temperatures mean a longer wildfire season.
Global warming also increases water vapor in the atmosphere, which can lead to more frequent heavy rain and snowstorms. A warmer and more moist atmosphere over the oceans makes it likely that the strongest hurricanes will be more intense, produce more rainfall, and possibly be larger. In addition, global warming causes sea level to rise, which increases the amount of seawater, along with more rainfall, that is pushed on to shore during coastal storms.
That seawater, along with more rainfall, can result in destructive flooding. The effect of global warming on the frequency, intensity, size, and speed of hurricanes remains a subject of scientific research.
Extreme weather events are influenced by many factors in addition to global warming. For example, many studies have linked an increase in wildfire activity to global warming. In addition to human-caused climate change, the risk of fire could depend on past forest management, natural climate variability, human activities , and other factors.
Oregon, Washington, and Colorado have also seen explosive fires that have forced thousands to evacuate, claimed lives, and destroyed homes and businesses. Experts are warning that widespread drought across the West will fuel another dangerous fire season in As global temperatures rise, the hottest temperatures — and the number of areas impacted by extreme heat — are also rising.
That means more scorching hot days in more places. Take the Texas cities of Austin and Houston, for example. Through , scientists predict hotter temperatures and more frequent and intense heat waves in every region of the U. Extreme heat increases demand for air conditioning, fueling carbon pollution and putting a strain our energy system that can lead to blackouts. It also poses a serious health threat, especially for the most vulnerable.
Higher temperatures also lead to drier conditions. When global temperatures rise, moisture evaporates from waterbodies and soil. Droughts in the U. In fact, the American West is currently in the midst of a mega drought that ranks among the worst in the past 1, years. Much of the region is currently facing "extreme" or "exceptional" drought conditions.
Warmer air increases evaporation, which means that our atmosphere contains an increasing amount of water vapor for storms to sweep up and turn into rain or snow. Just as drier areas are likely to get drier with rising global temperatures, those areas of the world that have historically trended toward heavy precipitation will only get wetter.
In the contiguous United States, rainfall in broke records, with an average of Hurricanes are growing more powerful as global temperatures rise because these storm systems draw their energy from warm ocean water. The Category 4 storm caused catastrophic damage to structures and suspected chemical fires among the region's petrochemical plants.
Virgin Islands, and Puerto Rico. Hurricane Katrina ripped into the Gulf Coast in August , devastating entire cities and hitting Black communities like those in low-lying New Orleans parishes especially hard.
Fifteen years after this costly disaster, our nation remains just as susceptible, if not more so, to the threat of increasingly violent hurricanes.
As the planet warms, ocean waters are also warming — and expanding. Right now, the Atlantic coast of the United States and the Gulf of Mexico are experiencing some of the highest sea level rise in the world, which, combined with record rainfall, has led to catastrophic flooding. Overall, winters are getting milder and shorter; but recent winters have brought intense snowstorms and record-breaking frost. While it may seem contradictory, climate change may be contributing to more extreme winter weather.
As the warming atmosphere traps water vapor later and later into the year, that precipitation leads to heavier snowfall when the temperatures do drop.
Two found no discernible link pdf, p , while one was inconclusive pdf, p3. Interestingly, a study analysed the way links between climate change and the California drought were portrayed in US media. The rest of this article looks at the evidence for the three most-studied types of extreme weather — heatwaves, heavy rain and floods, and droughts — as well as some of the main issues in event attribution, and where the field as a whole is heading. One study suggests that the Korean heatwave in the summer of had become 10 times more likely due to climate change, for example pdf, p The studies on extreme heat that did not find a role for climate change were an analysis of the Russian heatwave in and a rapid attribution study of the all-time high temperatures recorded in Rajasthan, India in May And climate change was found to play a role in all but one of the 14 Australian heat events studied.
It is worth noting for that one event, however, that although the study pdf, p was inconclusive for the city of Melbourne in southeast Australia, the authors did detect a human influence on extreme heat up the coast in Adelaide.
This raises a few important points. Attribution is about working out if the likelihood or magnitude of a particular event happening now is different from what it would be in a world that was not warming. A useful analogy — as explained in the first BAMS report in — is of a baseball player who starts taking steroids.
But it is possible to say how the steroids have altered the likelihood that the player hits a home run, by comparing their current and historical performances. As the report put it:. Another important point is that in cases where attribution science finds that climate change is making a given type of extreme weather more likely, it does not necessarily follow that the chance of experiencing that kind of weather gets incrementally higher each year.
Natural variability means that there will still be ups and downs in the strength and frequency of extreme events. Finally, there is usually a level of confidence attached to attribution results. So, while two studies might both find a role for human influence in a given weather event, the signal may be stronger for one than the other. For the purposes of this analysis, the attribution map does not distinguish between high- and low-confidence results, but users can click through to each study for more details.
That there is a more divided set of results for extreme rainfall than for heatwaves could suggest several things. In other cases, an inconclusive result could reflect the fact that rainfall or flooding events are inherently more complex than heatwaves, with many ways for natural variability to play a role. Human factors, such as land use and drainage, also play a part in whether heavy rain leads to flooding. Take the UK, for example. This raises another important point. When it comes to interpreting the results of event attribution studies, it matters what the question is.
For example, a study asked whether recent wet summers in northwestern European were a response to retreating Arctic sea ice pdf, p The paper notes that, in a chaotic weather system, the complex dynamics of the atmosphere mean the size and path of a storm or heavy rainfall event has a large element of chance.
This can make it tricky to identify where climate change fits in, potentially underestimating its influence. Higher temperatures mean warmer seas, higher sea levels and more moisture evaporating into the atmosphere.
These are changes that scientists can be more confident in, the authors write, and so should be the focus for attribution studies — rather than looking at changes to circulation patterns in the atmosphere.
For example, the paper reexamines an earlier study pdf, p15 that suggested climate change had reduced the chances of the five-day heavy rainfall event that hit north-east Colorado in September Trenberth and colleagues argue that while climate change might not have made the specific weather system that brought the rain more likely, it will have contributed to the sheer volume of moisture in the atmosphere.
While attribution studies of heatwaves are generally more straightforward than storms — as they focus on thermodynamic influences — the type of question they are asking is still important. The Russian heatwave in is a good example of this.
One study looking at the severity of the event did not find a role for climate change. Yet another one , which did find an influence, looked at the likelihood of the event.
This apparent contradiction is tackled by a third study that reconciles the other two. It is also important to stress that the absence of evidence for a link to climate change is not the same as evidence of absence. In other words, it does not necessarily mean there was no human influence, just that a particular analysis did not find one.
This is why a single study should never be considered the final word on how climate change influences a given type of extreme weather. Capetonians queue for water at natural springs around the city during the water crisis, January This mixed bag of results reflects the inherent complexity of droughts. And, again, the specific question matters. Conclusions about the role of climate change in a specific drought could depend on whether a study looks at temperature, precipitation or soil moisture, for example.
While much has been achieved in the field of extreme event attribution in a short space of time, scientists are constantly looking for ways to tailor their work to suit the people who might use it.
One major goal since the early days of the field has been to expand extreme event attribution to cover a larger and more diverse geographical area.
Where in the world scientists can carry out attribution studies — and for what kind of events — will always be limited by the quality and availability of observed data and appropriate models.
The attribution map highlights, for example, that there are relatively few studies of extreme weather in Africa and South America. But, at the moment, there is also a heavy leaning towards weather events that are local to the modelling groups, or that have a particular scientific interest. Otto explains:. The UK, California and Boulder [in Colorado] are, therefore, studied much more than other parts of the world, but that does not necessarily make them places particularly impacted by climate change.
This means that while the studies carried out so far are indicative of the role climate change is playing in extreme weather around the world, they should not be considered representative of all types of extreme weather everywhere, says Otto.
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