Extreme Weather Events

We investigate to what extent global warming affects extreme weather events, such as droughts, heatwaves, marine heatwaves, floods, hurricanes or other meteorological events. Are they becoming more frequent and/or more severe?
Extreme weather events - chasing a tornado in Wyoming
Waiting for a tornado in LaGrange, Wyoming, in a field command vehicle. Photo: © Dr Mike Coniglio. NOAA

How Does Climate Change Affect Extreme Weather Events?

In the days after a flood, wildfire, hurricane or other extreme weather events, people invariably ask: Was climate change the cause of it? It’s an obvious question, given the fact that we are seeing drier droughts, hotter heatwaves, bigger storm surges and more violent downpours of rain.

Actually, a better question is: does global warming make an extreme weather event more severe, or more likely to happen in the first place? After all, there have always been tornadoes and hurricanes, blizzards and severe thunderstorms. But is our climate crisis making things worse?

This article covers how climate science is searching for the human fingerprint in extreme weather events.

Worth Reading: What’s the Difference Between Climate and Weather?

What Is Meant By An Extreme Weather Event?

Firstly, let’s define what an extreme weather event is. It’s a weather event that is rare for a particular place and time of year. Usually it is severe or unseasonal weather. What exactly constitutes ‘rare’ can be hard to define, but the Intergovernmental Panel on Climate Change (IPCC) suggests that ‘rare’ means in the bottom 10 percent or top 10 percent of severity for a given type of weather in a given location. 1

Examples of extreme weather events include flash floods, large hail, deadly lightning, high winds, tornadoes (twisters), hurricanes, dust storms, wildfires and droughts.

Are Extreme Weather Events Becoming More Frequent?

Yes. According to a recent study by Stanford University, some extreme events are becoming more frequent. 2 Particularly those related to heat and rainfall. The researchers go on to say that, as our climate system becomes more unbalanced, extreme weather events are going to become increasingly more frequent, intense and widespread. But perhaps even more worrying, they conclude that everyone has been under-estimating just how bad it is going to get.

The reason for this false sense of security, researchers say, lies in the way we gather data to make climate predictions. Future weather predictions are traditionally made using historical weather observations.

The problem is, global warming is heating the ocean and atmosphere so rapidly, in ways that make historical records increasingly irrelevant.

This will cause problems for climate change mitigation and adaptation planning. After all, without accurate data, it is hard to understand how Earth’s climate system works and thus prepare for an increasingly hostile environment.

Researching Extreme Weather Events

This is why some researchers are now turning to a new area of research called ‘attribution’ research. Using a more conditional approach they hope to widen the net to identify the fingerprint of climate change in weather patterns more accurately. The most common way of carrying out an attribution analysis is to compare two sets of data:

First set of data: researchers take real world data and compare it with a computer simulation of an imaginary world, where people never started pumping carbon dioxide into the air and there is no global warming. The computer simulation starts around 1850, assuming pre-industrial emissions of greenhouse gases in the atmosphere. It runs the clock forward with no further emissions to generate possible scenarios. (Note: When Did Global warming Start?)

Second set of data: The above results are then compared with another set of data. The second data uses either real-world data from 1850-onwards or the results from simulation that do take into account anthropogenic climate change.

The researchers then analyze how often an extreme event occurs in each scenario. If an event shows up just as frequently in both models, the reasoning goes, climate change probably isn’t a factor.

Proponents of this new attribution method argue that it gives a more complete picture of the effects of global warming, compared to the conventional historical approach which could possibly be misleading.

For example, in 2013 Colorado suffered from flash floods, causing loss of life and severe damage to property. One 2017 study concluded that the floods were not linked to global warming. However, another report using ‘attribution’ methodology swiftly concluded the opposite, stating that the event became ‘extreme’ because of a 30 percent increase in rainfall connected to climate change.

The first attribution study was published in 2004 and since then, hundreds more have appeared. Scientists at Carbon Brief 3 have been tracking all the peer-reviewed extreme weather attribution studies, and so far the data shows:

  • Of the 355 extreme weather events tracked, 69 percent were made more likely or more severe by human-caused climate change.
  • Heatwaves account for 47 percent of such events, while floods, heavy rain and droughts each make up 15 percent.

While 69 percent of studies found that climate change did impact an event, the rest did not. So, either climate change didn’t play a role in those instances, or the tools used were not able to detect the fingerprint.

While climate researchers are still clashing over methodology, the increasing number of these types of studies show a growing push amongst researchers to develop more a robust approach to understanding the impact of climate change on weather.

Heatwaves

Unusually hot days and nights are a natural part of weather variation. However, as Planet Earth warms, scientists say that terrestrial heatwaves as well as marine heatwaves will become hotter, more frequent and last longer 4

In the United States, for example, heatwaves used to occur in major cities twice a year on average in the 1960s. This increased to six times in the 2010s. 5

Not only are hot days happening more frequently, but they are lasting longer. The average heatwave season lasts 47 days longer than in the 1960s. It is difficult even for the climate change denial movement to ignore this fact.

When it comes to human life, the most dangerous effect of heatwaves occurs because of both high humidity and elevated temperature – especially if those conditions last more than two days.

Such conditions force the heart to pump harder in an attempt to regulate body temperature. Between the years 1998-2017, more than 166,000 people died due to heatwaves, including the 70,000 who died during the 2003 European heatwave.

Heatwaves also cause strain on emergency services, water supplies, and also blackouts, due to an energy demand surge as people switch on their air conditioning.

As the climate crisis worsens and we continue to exceed global temperature projections – the number of people exposed to heatwaves has increased by 125 million between the years 2000 and 2016. 6

Heatwaves also impact ecosystems. For example, in 2015 and 2018, hundreds of kilometers of coastal mangroves in Australia’s Gulf of Carpentaria were wiped out by a combination of drought, heatwaves and sea-level falls due to extreme variation in the El Nino weather system. 7

Studies also show that climate change is unbalancing the El Niño-Southern Oscillation, causing more extreme weather events around the Pacific Basin. 8

Similar climate variability is occurring in the western and eastern areas of the Indian Ocean, due to the Indian Ocean Dipole weather cycle and the travelling Madden-Julian Oscillation (MJO).

Are You Studying Climate Change?

If so, then you’ll enjoy these articles:

Droughts

Drought is also affected by climate change. Important agricultural and forested regions around the world, can expect more frequent and intense droughts and rainfall.

This was the conclusion of researchers at the American Geophysical Union who used the latest generation of climate models known as CMIP6 to produce their data. This data will inform the next IPCC assessment report on climate change. 9 The models found that drought intensity and duration was directly linked to levels of greenhouse gases in the troposphere.

Meantime, research from McGill University found that simultaneous heatwaves and droughts are becoming increasingly common in western parts of the U.S. These periods of hot and dry weather are impacting the water cycle, making wildfires larger and more frequent. 10

In fact wildfires are becoming so intense that we need a new vocabulary just to describe them. 11 A gigafire is a term for a blaze that burns at least one million acres of land. It is the next level above a megafire which burns over 100,000 acres. The Australian bushfires of 2019-2020, and the Californian fires of 2020 are gigafires.

Researchers note that the triggers for these hot-dry extreme weather events are changing. Back in the 1930s during the catastrophic Dust Bowl era, the dust storms were driven by lack of rainfall and poor farming practices. In recent times however, dry-hot disasters are driven more by excess heat than lack of rain.

Did You Know?

Modern farming techniques in the western world operate an industrial model that takes them far away from nature. It is a model that neglects soil health, reduces biodiversity and relies too heavily on pesticides and fertilizers. For more, see: Why Is Soil So Important to the Planet?

This leaves western farmers very susceptible to climate change and extreme weather events. For more read: 7 Effects of Climate Change on Plants.

Floods

Climate change is directly linked to rising sea levels, and higher storm surges. This places many low-lying communities and countries at significant risk of flooding.

The IPCC’s Fifth Assessment report projected a rise of sea level up to 90 cm (3 feet). According to NASA, levels are projected to rise by 1-4 feet by 2100. 12 

Some later studies by the U.S. NOAA, and others, indicate that a sea level rise of up to 200-270 cm (6.5 to 9 feet) this century, is possible. 13

But, the worst floods are not caused by rising seas. They are caused by storm surges that piggy-back on rising seas. This combination is making flooding much more deadly. In temperate seas, storm surges can raise water levels by an additional 3 meters (10 ft), while in the tropics the rise can be as high as 8 meters (26 ft).

In addition to the impact that storms have on communities, it also causes significant stress and damage to important marine ecosystems like coral reefs, as well as coastal ecosystems that harbor valuable blue carbon reserves in kelp forests, seagrass meadows and mangrove swamps.

Supercell storm, Kansas. The type of severe thunderstorm system that produces tornadoes.
Supercell storm in Kansas. This is a type of severe thunderstorm that can produce giant hailstones, torrential rainfall, as well as winds and tornadoes. As storms feed off latent heat, this is one reason why scientists think global warming is intensifying storms. Photo: © Mike Coniglio, NOAA National Severe Storms Laboratory

Storms and Hurricanes

Are storms getting worse? Are we seeing more severe hurricanes, cyclones and typhoons? The answer is Yes, it seems so.

Scientists are now blaming climate change with more confidence, after a recent study was published by the National Oceanic and Atmospheric Administration. 14

The study shows that the odds of Category 3, 4 and 5 hurricanes are increasing because of human-caused global warming. This finding builds on previous research which had identified a trend, but was not statistically robust.

Given that hurricanes get their energy from warm ocean waters and water vapor in the air, these findings are consistent with what scientists expect to happen as the world warms. For example, we now know that the rainfall from Hurricane Harvey was 15 percent more intense and three times as likely to occur, because of anthropogenic climate change.

Needless to say, insurance firms are bracing themselves for a major increase in claims.

NOTE: Hurricanes and other large storm systems are generally considered to be influenced by global warming. Tornadoes, however, are not. They are mainly influenced by a combination of local weather factors such as temperature and wind shear.

Top 10 Worst Extreme Weather Events

Storm NameCountries AffectedDamage
(billion US$)
Hurricane Katrina – Sept 2005USA156
Hurricane Harvey – Aug 2017USA95
Hurricane Irma – Sept 2017USA & Caribbean80
Hurricane Maria – Sept 2017Caribbean & USA69
Hurricane Sandy – Oct 2012USA & Caribbean53
Floods – July & Aug 1998China44
Floods – Aug 2011 to Jan 2012Thailand43
Hurricane Ike – Sept 2004USA & Caribbean36
Hurricane Ivan – Sept 2004USA, Caribbean, Venezuela29
Hurricane Wilma – Oct 2005USA, Mexico, Belize, Honduras, Caribbean25
The huge damage inflicted by the 3 storms – Hurricane Harvey (US$ 95 billion), Hurricane Maria (US$ 70 billion) and Hurricane Irma (US$ 81 billion) – was dwarfed only by Hurricane Katrina in 2005, which cost US$ 156 billion. Source: Economic Losses, Poverty and Disasters (1998-2017) by Centre for Research on the Epidemiology of Disasters (CRED) and UNISDR. 6
Hailstorm damage to vehicles during extreme weather events
Hailstorm damage to a car used by NOAA scientists while they were storm chasing. Hail can damage cars, homes, airplanes and can be deadly to livestock and people. In the U.S. Nebraska, Colorado and Wyoming usually have the most hailstorms. Studies indicate that hailstorm damage will increase in the future, in line with rising temperatures. It is estimated that the annual damage to farming could increase by 25 to 50 percent by 2050. Greenhouse horticulture impacts could be much worse, in the region of 200 percent. 15 Photo: NOAA

More Rainfall

While much of the focus has been on a warming world – there will also be major changes in precipitation – that is rain and snowfall. Sometimes we forget, that excess rain and snowfall are also considered extreme weather events.

As air warms it can hold more moisture – in fact the air can hold about 7 percent more water vapor for every 1C rise in temperature. So if the planet heats up by 4C, there will be around 28 percent more water vapor in the atmosphere.

That rain won’t fall evenly across the planet, some areas will get more and others less. In general, if you live in a place that traditionally rains a lot (like Ireland) – it will rain more. If you live in a drier region, it will become even drier. For example, the Mediterranean region will have 20 percent less precipitation by 2100 in an RCP8.5 world. 16 The hydrosphere is constantly adapting.

Unfortunately, rising temperatures near the equator mean less rainfall  for places like the Amazon Rainforest in Brazil. This forest actually makes half its own rainfall through transpiration by trees and plants. As the rainforest receives less rainfall, trees can’t absorb enough water, and so in turn make less rainfall – creating a climate feedback loop. Eventually the forest morphs into a drier type of biome through a process known as savannization.

References

  1. Heatwaves, droughts, tornadoes and hurricanes. NOAA []
  2. Global warming influence on extreme weather events has been frequently underestimated 2020. Science Daily []
  3. Mapped: How climate change affects extreme weather around the world. CarbonBrief.org []
  4. Climate Science Special Report Executive Summary []
  5. US Heatwaves Frequency – Globalchange.gov []
  6. CRED and UNISDR Report – https://www.preventionweb.net/files/61119_credeconomiclosses.pdf [][]
  7. “Shocked scientists find 400km of dead and damaged mangroves in Gulf of Carpentaria.” Guardian. Oct 3, 2019. []
  8. “Historical change of El Niño properties sheds light on future changes of extreme El Niño.” Bin Wang, et al. PNAS November 5, 2019. 116 (45) 22512-22517. []
  9. Robust future changes in meteorological drought in CMIP6 projections despite uncertainty in precipitation. Geophysical Research Letters, 2020. Anna M. Ukkola et al. []
  10. McGill University. “Disastrous duo: Heatwaves and droughts: Climate change at the heart of more frequent and intense dry and hot extremes in recent decades.” ScienceDaily. ScienceDaily, 28 September 2020 []
  11. “California fire is now a ‘gigafire,’ a rare designation for a blaze that burns at least a million acres”. CNN, October 2020. []
  12. Sea Level Will Rise 1-4 feet by 2100.” NASA.[]
  13. “Global and Regional Sea Level Rise Scenarios for the United States.” NOAA Technical Report NOS CO-OPS 083. National Oceanic and Atmospheric Administration. January 2017. []
  14. Global increase in major tropical cyclone exceedance probability over the past four decades. J.P. Kossin et al. June 2020. []
  15. “Climate change and hailstorm damage: Empirical evidence and implications for agriculture and insurance.” 2009 W.J.W.Botzena, L.M.Bouwera, J.C.J.M.van den Bergh []
  16. “What climate models tell us about future rainfall”. Carbon Brief. []
Share on facebook
Share on twitter
Share on linkedin
Share on whatsapp
Share on email