The big tornado outbreak, including a monster Oklahoma twister, have people asking again about a possible link to climate change. I’ll review the science in this post.

“The news helicopter from kfor.com caught this image of the shocking near-total destruction of a huge area of Moore, Oklahoma, on May 20, 2013.” Via Masters.

Tom Karl, the director of the National Climatic Data Center, explained in a 2011 email:

What we can say with confidence is that heavy and extreme precipitation events often associated with thunderstorms and convection are increasing and have been linked to human-induced changes in atmospheric composition.

Insured losses due to thunderstorms and tornadoes in the U.S. in 2012 dollars. Data and image from Property Claims Service, Munich Re.

Tornadoes “come from certain thunderstorms, usually super-cell thunderstorms,” explained climatologist Dr. Kevin Trenberth in an email today, but you need “a wind shear environment that promotes rotation.” Global warming may decrease the wind shear and that may counterbalance the impact on tornado generation from the increase in thunderstorm intensity.

Trenberth, the former head of the Climate Analysis Section of the National Center for Atmospheric Research, notes:

The main climate change connection is via the basic instability of the low level air that creates the convection and thunderstorms in the first place. Warmer and moister conditions are the key for unstable air.

The climate change effect is probably only a 5 to 10% effect in terms of the instability and subsequent rainfall, but it translates into up to a 32% effect in terms of damage. (It is highly nonlinear). So there is a chain of events and climate change mainly affects the first link: the basic buoyancy of the air is increased.  Whether that translates into a super-cell storm and one with a tornado is largely chance weather.

After April 2011 saw records set for most tornadoes in a month and in 24 hours — “The Katrina of tornado outbreaks“ — I examined the climate/tornado link in great detail here, looking at the data, the literature, and expert analysis. That piece concluded:

1. When discussing extreme weather and climate, tornadoes should not be conflated with the other extreme weather events for which the connection is considerably more straightforward and better documented, including deluges, droughts, and heat waves.
2. Just because the tornado-warming link is more tenuous doesn’t mean that the subject of global warming should be avoided entirely when talking about tornadoes.

Early March 2012 saw what was likely “the most prolific five-day period of tornado activity on record for so early in the year,” as meteorologist Dr. Jeff Masters put it.

Then we had an unusually long “tornado drought” from May 2012 to April 2013, which has now come to a stunning end, punctuated by the devastating Moore, Oklahoma tornado yesterday:

A massive, mile-wide supercell tornado ripped through the suburbs of Oklahoma City, destroying homes, schools and other buildings. The tornado was on the ground for some 40 minutes, according to the National Weather Service (NWS), and police reported that an occupied elementary school was in the path of the cyclone. Early estimates had winds on the ground near 200 mph, which would have made the cyclone an F4 or higher. Witnesses said the damage was like something out of an atomic bomb strike, and there are at least 24 people dead, including many young children, with a toll that could eventually be far higher.

Masters says “the Moore tornado likely to be one of the five most damaging tornadoes in history,” which is particularly tragic because Moore had “previously experienced the 4th costliest tornado in world history, the notorious May 3, 1999 Bridgecreek-Moore EF-5 tornado.”

You can donate to the American Red Cross disaster relief here.

Below is an extended review of the scientific literature along with some analyses from this year and last year by leading experts.

Read more

Our guest blogger is Brad Johnson, campaign manager of Forecast the Facts

Countless lives were saved this weekend by vigilant government officials who warned of deadly tornadoes in Oklahoma, Kansas, Iowa, Nebraska — states whose politics are dominated by anti-government, anti-science ideologues. Over 100 tornadoes struck down in 24 hours, but only six people died in Oklahoma, Sen. Jim Inhofe’s home state, thanks to warnings from the National Weather Service scientists he has worked to discredit:

The tornadoes were unrelenting – more than 100 in 24 hours over a stretch of the Plains states. They tossed vehicles and ripped through homes. They drove families to their basements and whipped debris across small towns throughout the Midwest. In some areas, baseball-size hail rained from the sky.

And yet, in a stroke that some officials have attributed to a more vigilant and persistent warning system, relatively few people were killed or injured.

Wichita, Kansas, the headquarters of Koch Industries, suffered $280 million in damage from a ferocious twister, but the “ever-increasing government” demonized by the Koch brothers prevented any loss of life.

Greenhouse pollution from the fossil fuel industries that control the region’s politics is making our weather more extreme and dangerous. The heat trapped by carbon pollution is powering these earlier and more intense storms with record-warm waters in the Gulf of Mexico. As Dr. Jeff Masters wrote on Friday:

This is the warmest March value on record for the Gulf of Mexico, going back over a century of record keeping. During the first two weeks of April, Gulf of Mexico waters remained about 1.5°C above average, putting April on pace to have the warmest April water temperatures on record. Only one year in the past century has had April water temperatures in the Gulf of Mexico more than 1.1°C above average; that year was 2002 (1.4°C above average.) All that record-warm water is capable of putting record amounts of water vapor into the air, since evaporation increases when water is warmer. Because moist air is less dense than dry air, this warm, moist air flowing northwards from the Gulf of Mexico into the developing storm system over the Plains will be highly unstable once it encounters cold, dry air aloft. The record-warm waters of the Gulf of Mexico are a key reason for the high risk of severe weather over the Plains this weekend.

Related Post:

• Tornadoes, Extreme Weather and Climate Change, Revisited

Carbon pollution from fossil fuels is poisoning the weather, helping drive the conditions that created the killer tornado outbreak last week across the heart of the United States. More than 85 tornadoes killed at least 38 people and devastated communities in ten states. The furious storms formed as a strong cold front from the north crashed into high humidity and warm temperatures from the south.

Meteorologist Jeff Masters explained to USA Today that the warm, humid air that fed the tornadoes comes from an unusually hot Gulf of Mexico:

“This year’s unusually mild winter has led to ocean temperatures across the Gulf of Mexico that are approximately 1 degrees C (1.8 degrees F) above average,” says meteorologist Jeff Masters of the Weather Underground. This places it among the top ten warmest values on record for this time of year, going back to the 1800s, he says. “Friday’s tornado outbreak was fueled, in part, by unusually warm, moist air flowing north from the Gulf of Mexico due to the high water temperatures there,” Masters says. He says this exceptionally warm air set record high temperatures Friday afternoon at 28 airports in Louisiana, Arkansas, Mississippi, Alabama, Tennessee, Kentucky, and Georgia. Warmer winters — and an earlier arrival of spring due to a warming climate — will allow tornado season to start earlier and end earlier. “This year’s early start to tornado season is consistent with what we would expect from a warming climate.”

“Baseline ocean temperatures have indeed warmed because of global warming,” Masters told ThinkProgress Green in a follow-up, “so part of the hot Gulf of Mexico temperatures can be blamed on global warming.”

“It is irresponsible not to mention climate change,” climatologist Kevin Trenberth of the National Center for Atmospheric Research told ThinkProgress Green last year. “The environment in which all of these storms and the tornadoes are occurring has changed from human influences (global warming).”

“As spring moves up a week or two, tornado season will start in February instead of waiting for April,” Trenberth told Reuters this week. The winter season from December to February was the fourth warmest on record for the lower 48 states, according to the National Oceanic and Atmospheric Administration (NOAA).

“Inherently the global warming from humans is quite small from one year to the next, but 10 times larger from one decade to next, and so on,” Dr. Kevin Trenberth told ThinkProgress Green in an email interview. With over a hundred years of man-made global warming from the start of the Industrial Revolution, the cumulative effect of greenhouse pollution has become significant enough to change ocean temperatures and regional weather patterns in measurable ways. “But superposed is all the shorter term natural variability that at any time can offset that or amplify it,” Trenberth cautioned.

Because of that variability and imperfect historical records, scientists have not found a measurable trend in tornado intensity and number. However, with greater greenhouse pollution scientists expect changes. “The number of days when conditions exist to form tornadoes is expected to increase” as the world warms, atmospheric scientist Robert Trapp told Reuters.

Scientists are only beginning to have a formal understanding of how our disruption of the global climate is influencing extreme weather such as tornado-bearing thunderstorms. However, a picture is beginning to emerge, NASA climate scientist Anthony D. Del Genio wrote in 2011: “As the climate warms, we might experience fewer storms overall, but more of the strongest storms.” They have identified the risk of longer tornado seasons with stronger thunderstorms. Meanwhile, right-wing austerity policies are causing cutbacks in weather monitoring, infrastructure maintenance, and emergency preparedness.

In the face of this warning, we must ask if our current path of increased pollution and decreased investment in public safety is the wisest course.

Killer tornadoes are marking the transition from a freakishly warm winter into yet another freakishly dangerous spring. The multi-billion-dollar drought in Texas and Oklahoma is expected to continue into the indefinite future. Planting seasons, maple syrup seasons, and cherry blossom festivals are starting at weirder and weirder times. Torrential rains and record heat waves are becoming commonplace. Migrating birds are straying from their normal path, insect pests are multiplying, and trees are dying.

Americans are starting to trust the evidence of their own senses about the growing impacts of climate change, instead of the barrage of misinformation and confusion that comes from media sources. A new poll from the Brookings Institution shows that a strong majority of the American public agree that there is “solid evidence that average temperatures on earth have been getting warmer over the past four decades,” and “about half of Americans now point to observations of temperature changes and weather as the main reasons they believe global warming is taking place”:

A sampling of the open-ended comments provided by survey respondents helps demonstrate the role that weather plays in shaping individual views on global warming. A male senior citizen from Illinois, who feels that there is solid evidence of global warming, said that the primary reason that led him to this conclusion was “winters just aren’t as cold as they were in the past.” Similarly, a middle-aged woman in Florida attributed her position on global warming primarily to her observations that “this time of year is warmer than it is expected to be.” A young man in Texas identified the primary reason for his view that the Earth is warming to “temperatures last summer that were awful,” while another young Texan stated that the “droughts this past summer” were the primary reason that she believed temperatures on earth were increasing. In these cases and many others Americans turn first to the weather they experience as the key reason for their acceptance of global warming.

This intuitive, natural approach tying the long-term warming of the entire planet by fossil-fuel pollution to local observations is backed by the science. Scientific research has determined that the continental United States is growing hotter in every state, with greater extremes in precipitation. The warming of the oceans and atmosphere has fueled the freak droughts and heat waves that the poll respondents cited. In almost every measure, the weather of the United States has diverged perceptibly from the 20th-century norm — in line with scientific projections of the consequences of global warming pollution.

In 1988, NASA climate scientist James Hansen predicted that the local changes in temperature caused by global warming pollution would become apparent in everyday life by the 21st century. That prediction has now come to pass — despite billions of dollars spent by polluters to argue against the evidence of people’s own senses.

In short, our weather has been poisoned by the fossil fuel industry, and every day more and more Americans know it, just by going outside.

As carbon pollution accumulates in the atmosphere, our weather is growing more intense and unpredictable, threatening the health of the union. Following the freakishly warm and dry start of this January, extreme storms then pummeled the nation:

WASHINGTON ICE STORM: “A monster Pacific Northwest storm coated the Seattle area in a thick layer of ice Thursday and brought much of the state to a standstill, sending hundreds of cars spinning out of control, temporarily shutting down the airport and knocking down so many trees that members of the Washington State Patrol brought chain saws to work. East of Seattle, a man was killed by a falling tree as he was backing an all-terrain vehicle out of a backyard shed, authorities said.” 90,000 customers of Puget Sound Energy lost power.

OREGON FLOODS: With a persistent flow of Pacific moisture targeting the Pacific Northwest, several inches of rain have fallen across the western third of Oregon. Widespread flooding has developed with Salem, Corvallis and Philomath just some of the cities that have dealt with the worst of the rising waters. Torrential rain swept away a car from a grocery store parking lot, killing a mother and her one-year-old son.

NEVADA WILDFIRE: A destructive wildfire erupted shortly after noon on Thursday and raced quickly through the dry countryside surrounding Reno, NV, propelled by wind gusts of 82 mph. At its height, the fire forced evacuation calls for some 10,000 people. The fire destroyed 29 homes over six square miles before a storm on Saturday brought precipitation after the region’s driest winter in recorded history. Reno had no precipitation at all in December.

JANUARY TORNADOES: Last Tuesday, a powerful storm front spawned one EF-1 tornado in metropolitan Louisville, Kentucky, and a second hit near Madison, Indiana. At least 10 tornadoes struck the South overnight Sunday as a powerful storm system moved across the Great Lakes and into southern Canada, killing two in Alabama. The tornadoes were spawned along the southern end of a front that arced through the eastern US like a comma’s tail, bringing severe thunderstorms, hail, and twisters to Arkansas, Mississippi, Alabama, and Tennessee before moving into Georgia later Monday morning.

Extreme weather is wreaking increasing damage on the people of the United States. With cutbacks in local, state, and federal government services, continued inaction on fighting greenhouse pollution, and ideological opposition to preparing for the ravages of unchecked climate change, the state of our union is under threat.

As fossil fuel pollution heats the planet, one of the casualties is the traditional celebration of the founding of the United States. The record droughts, floods, and storms fueled by global warming are causing widespread bans on fireworks and the cancellation of numerous municipal firework displays, even a celebration for our soldiers in Oklahoma:

There will be no fireworks this year exploding over Fort Sill in Lawton. The U.S. Army base’s Independence Day celebration and concert will go on as planned Saturday, but its fireworks have been canceled. A fire that started on a base firing range last week burned across 5,500 acres before it was contained. Thirteen homes were destroyed and 1,500 people had to be evacuated.

Firework shows from Texas to Massachusetts have been canceled because of the deadly climate conditions:

In Oklahoma, 36 counties suffering from extreme to exceptional drought have issued burn bans, which include a prohibition on fireworks except for public displays.

In Kansas, fireworks have been banned in Dodge City and surrounding rural areas due to the extreme drought.

In Louisiana, fireworks have been banned in Shreveport and neighboring Bossier because of extreme heat and drought.

In Texas, 170 counties have fireworks bans, including all of metropolitan Houston. Nearly all of Texas has burn bans as well. Because of the extreme drought, Fourth of July fireworks displays have been canceled in Texas towns large and small: San Antonio, Austin, Amarillo, Lubbock, Plainview, Magnolia, Tomball, DeSoto, Woodlands, Roman Forest, and Patton Village.

In Arizona, authorities have banned fireworks from Flagstaff in the north to Tucson, Douglas and Sierra Vista in the south.

In New Mexico, Gov. Susana Martinez (R-NM) has said that there is “absolutely no reason to buy, sell or use personal fireworks.” She has declared a “state of emergency in New Mexico regarding the use of fireworks.” Albertson’s, WalMart, and Smith’s stores have stopped selling fireworks in the state. Taos, with wildfires raging nearby, has canceled its fireworks display.

In Joplin, Missouri, where a devastating tornado hit on May 22, officials have banned fireworks because of the amount of combustible debris in the tornado’s path.

In Massachusetts, the historical recreation site Old Sturbridge Village has canceled its fireworks display because its fireworks launch site was flooded and alternative launch sites were damaged by tornadoes.

Austerity budgets are also killing Fourth of July celebrations, with fireworks displays canceled at Jones Beach in New York, in Chicago, Illinois, and in Shawnee, Oklahoma.