What causes a tornado?
Tornadoes are formed by a combination of atmospheric instability and wind shear. Instability occurs when warm, moist air is wedged under drier, cooler air aloft. This warm air rises, causing the intense updrafts and downdrafts seen in strong thunderstorms — the incubators of tornadoes. Wind shear refers to changes in wind direction and speed at different elevations in the atmosphere. The combination of instability and wind shear forms the circular air flow that generates a tornado.
Why are there so many in the U.S. Midwest?
The Central United States has an abundance of the ingredients necessary for tornado formation. During the spring, warm tropical air masses from the Gulf of Mexico collide with colder, drier air at higher altitudes to spawn intense thunderstorms. Thunderstorms also form into the summer and fall, as the region’s vast plains heat up air near the surface, causing atmospheric instability. These intense thunderstorms act as incubators for tornadoes. Tornadoes occur around the world but are most common in “Tornado Alley” of the Central United States.
Is there a link between climate change and tornadoes?
It is important to keep in mind that climate change has an impact on all weather events. The effect of the carbon dioxide in our atmosphere cannot be switched off – it influences our seemingly benign “everyday” or “normal” weather as well as the extreme events.
A specific link between tornadoes and climate change, however, is unclear. It is difficult to identify and diagnose trends in long-term records of tornadoes, since the population in many areas affected by tornadoes has grown (e.g., tornadoes in the early part of the 20th century may have occurred without anyone seeing them) and the technology used to observe tornadoes has improved (e.g., radars help us “see” tornadoes in ways that were not possible many decades ago).
How could climate change affect the frequency or intensity of tornadoes?
Researchers are working to better understand how the building blocks for tornadoes -- atmospheric instability and wind shear -- will respond to global warming. It is likely that a warmer, moister world would allow for more frequent instability. However, it is also likely that a warmer world would lessen chances for wind shear. Recent trends for these quantities in the Midwest during the spring are inconclusive. It is also possible that these changes could shift the timing of tornadoes or regions that are most likely to be hit.
Adding to the difficulty, tornadoes are too geographically small to be well simulated by climate models. Models can simulate some of the conditions that contribute to forming severe thunderstorms that often spawn tornadoes. Multiple studies (e.g., here and here) find the conditions that produce the most severe thunderstorms are likely to occur more often in the in a warmer world, even if the total number of thunderstorms decreases (because of fewer weak storms). However, this work does not conclusively tell us whether tornadoes should follow the same trend as their parent thunderstorms.
Extreme Weather Event Map: Click on any icon on the map above to see details on the extent of an extreme weather event between 1990 and 2012.
Extreme Weather Events Map
The events shown above are examples of four types of extreme weather that scientists say are becoming more frequent and intense because of climate change: extreme heat, drought, wildfires, and heavy precipitation. Individual events cannot be blamed on any single cause. However, the long-term trends in these types of events demonstrate that extreme weather risk is rising as a result of climate change. Each new event is an opportunity to better understand our vulnerabilities and ways to cope with these rising risks. Examined together, these events also can help us evaluate the benefits of actions and policies aimed at reducing the emissions of heat-trapping gases that are warming the planet and “juicing up the weather”.
Here are two C2ES papers taking a closer look at the trends shown in the map and how we can respond:
- Extreme Weather and Climate Change: Understanding the Link, Managing the Risk
This primer examines the link between extreme weather and climate change, presenting it in a risk management framework that can help to clarify and manage the rising risk of extreme weather and prepare for future vulnerabilities.
- A Climate of Extreme Weather Events
This background paper outlines the evidence showing the increasing risk and incidence of flooding, heat waves, wildfires and drought in the United States.
Scientific American Series on Extreme Weather, Climate Change, and the Risks We Face
Published in three parts in June 2011, this series in Scientific American provides firsthand accounts of record-breaking weather events, insights into their links to climate change, and what can be done to manage the growing risks. The articles were written by science journalist John Carey with support from C2ES.
- Part One - Storm Warnings: Extreme Weather Is a Product of Climate Change
- Part Two - Global Warming and the Science of Extreme Weather
- Part Three - Our Extreme Future: Predicting and Coping with a Changing Climate
Additional C2ES Resources
Find answers to some of the most frequently asked climate science questions and learn about the realities and misconceptions of climate change science.
Learn how Hurricane Sandy is a stark reminder of the rising risks of climate change.
See the latest on the 2012-2013 U.S. drought, its costs at home and its impacts on the rest of the world.
Keep up to date on current extreme weather events, climate change, and risk management.
I live in one of those northern and western suburbs of DC that tend to lose power fairly frequently.
It used to be that one of the few nice things about losing power was the sound of silence. But those days are gone. Now losing power has a new sound: the whirring of the startup of my neighbors’ backup generators.
We need power not only to keep our food from spoiling and protect us from uncomfortable and even dangerous heat, but also to stay connected. As a nation, we are becoming ever more dependent on electronic devices. We cannot survive without our cell phones and computers, let alone our refrigerators and air conditioners. At the same time, climate change threatens the reliability of the grid through more intense heat waves and potentially more powerful storms.
While it’s easy to say we should work to prevent disruption in electricity, how much should we invest to bolster the resilience of the grid? And who should pay?
As Hurricane Sandy moves out of the region, people in affected areas are beginning to take stock of the damage. Flooding in parts of New Jersey and New York from the storm surge hit record levels. The 13.8-foot surge measured at Battery Park in Lower Manhattan surpassed the all-time record of 11.2 feet set in 1821, flooding the New York subway system and two major commuter tunnels. Along the Eastern Seaboard, an estimated 7.5 million people lost power. Farther inland, blizzard conditions dropped as much as 2 feet of snow as Sandy crashed into arctic air over the Midwest. While early estimates indicate direct damages from the hurricane may be as much as $20 billion, the total economic losses, including losses in consumer and business spending, could be more than twice that amount.
A number of climate change-related factors may well have intensified the storm's impact: higher ocean temperatures, higher sea levels, and an atmospheric traffic jam that may be related to Arctic melting. Hurricane Sandy is also a clear reminder of how vulnerable our homes and infrastructure already are to extreme weather — and this risk is growing.
A report released this week by two senior members of Congress notes that the unusual number of extreme weather events in 2012 has cost the country billions of dollars and that the unusual frequency of these events is consistent with what scientists have predicted from climate change.
The staff report, “Going to Extremes: Climate Change and the Increasing Risk of Weather Disasters” is from the offices of Reps. Edward Markey (D-MA) and Henry Waxman (D-CA), the prime movers behind the last attempt at significant climate legislation. It cites information from a variety of sources, including NOAA, the news media and the private sector to show how rising weather risk costs real money.
Their report comes a week after Congress headed home for the elections having accomplished very little to address climate change. Nearly half the bills introduced by the current Congress would block or hinder climate action, though none of these have been enacted into law.
July 31, 2012
Contact: Laura Rehrmann, 703-516-0621, email@example.com
C2ES Releases New Extreme Weather Map on Eve of Senate Climate Hearing
The Center for Climate and Energy Solutions (C2ES) has created a new online map providing an overview of extreme U.S. weather events since 1990. The map highlights examples of extreme heat, heavy precipitation, drought, and wildfire -- four types of events with clear trends connected to climate change.
In a blog post announcing the new map, C2ES science and policy fellow Dan Huber summarizes the recent run of extreme weather:
- The last 12 months were the hottest on record for the lower 48 states by a significant margin. The “Summer in March” heat wave broke thousands of heat records across the country.
- Almost as soon as the spring heat subsided, wildfires sprang up in the West, with New Mexico’s largest wildfire on record and Colorado’s most damaging fire occurring within weeks of each other.
- The United States is mired in the most extensive drought since 1956. Nearly two-thirds of the contiguous U.S. is currently in drought and 75 percent of that area is categorized as severe. Last year, Texas had its most severe drought ever, resulting in billions of dollars in agricultural losses.
“Climate change is elevating the risk of extreme weather,” writes Huber. “It’s crucial that we take stock of what each disaster teaches us so that we understand the rising risks and are better prepared for what’s to come.”
The science behind climate change will be the focus of a hearing tomorrow (Wednesday, Aug. 1) before the Senate Environment and Public Works Committee titled “Update on the Latest Climate Change Science and Local Adaptation Measures.” The hearing, set for 10 a.m. in 406 Dirksen, is the Senate’s first in this Congress focusing directly on climate change science.
For more information:
Extreme weather map: http://www.c2es.org/science-impacts/extreme-weather
Climate Compass blog: http://www.c2es.org/climatecompass
Contact Senior Communications Manager Laura Rehrmann at firstname.lastname@example.org to arrange an interview with a C2ES expert.
About C2ES: The Center for Climate and Energy Solutions (C2ES) is an independent non-profit, non-partisan organization promoting strong policy and action to address the twin challenges of energy and climate change. Launched in November 2011, C2ES is the successor to the Pew Center on Global Climate Change.
Today we’re updating our online map providing an overview of extreme weather events in the United States since 1990. The map highlights memorable examples of extreme heat, heavy precipitation, drought, and wildfire, four types of events with clear trends connected to climate change.
I recently responded to a question on the National Journal blog, "Does climate change cause extreme weather like the heat waves much of the country has been enduring for the past few weeks?"
With the Senate set to vote today on fixes to the ailing National Flood Insurance Program (NFIP), a new C2ES brief explains why the program is chronically in debt to the U.S. Treasury, and how to make it solvent. We urge, among other things, that Congress allow federal underwriters to begin taking into account rising flood risk due to climate change.
The 44-year-old federally-backed NFIP covers 5.6 million American households and more than $1 trillion in assets in flood-prone areas along rivers and coasts. Flooding is not an easy risk to insure, so historically private insurers chose not to. But in assuming that role, the NFIP has at times served to encourage rather than contain risk, and has racked up $18 billion in debt in the process.
With headlines like “Warmest spring heats up economy,” readers weary of bad economic news might be forgiven for thinking that a little global warming is not such a bad thing. But the warming we’ve experienced globally over the past 30 years is more than “a little.” And in the U.S., it’s likely contributing to drought and wildfires in the West and more extreme weather nationwide.
This past May came in as the second warmest on record globally, trailing only May of 2010. For land area only, it was the warmest on record, at 2.18 degrees F above average. It was also the 36th consecutive May, going back to 1976, with global temperatures above the 20th-century average.