Does Cold Weather Disprove Global Warming?

 

To The Teacher:


At the beginning of 2018, much of the country experienced cold weather, with​ some areas experiencing record-breaking low temperatures. The frigid weather led some people to ask whether the winter chill might disprove the idea that global warming is a problem. In fact, this has been a major talking point of climate-change deniers, one repeated every winter season. President Donald Trump tweeted this argument, suggesting that our country could use more global warming.

This lesson includes two student readings and discussion questions. The first reading examines how some politicians have used the cold weather argument to deny climate change. The second explores the science and statistics behind this common misconception, explaining why individual data points taken from personal experience should not be confused with an overall global trend.

After Reading 2, consider showing or pointing students to this short video, which offers a visual example of the importance of trend and variation discussed in the reading. Using the example of a person walking a dog, the video demonstrates how a data set may have many variations (represented by the seemingly random footsteps of the meandering dog) while the trend (represented by the direction the dog’s owner sets for the walk) remains consistent.

 


 

Reading One:
Politicians Respond to Cold Weather


At the beginning of 2018, much of the country experienced cold weather, with​ some areas experiencing record-breaking low temperatures. The frigid weather led some people to ask whether the winter chill might disprove the idea that global warming is a problem. In fact, this has been a major talking point of climate-change deniers, one repeated every winter season. In January 2018, President Donald Trump made a version of this argument in a tweet: “In the East, it could be the COLDEST New Year’s Eve on record. Perhaps we could use a little bit of that good old Global Warming that our Country, but not other countries, was going to pay TRILLIONS OF DOLLARS to protect against. Bundle up!”

This was not the first time that Donald Trump has used cold weather to take a jab at efforts to curb global climate change. Vox reporter Dylan Matthews found that Donald Trump has tweeted his skepticism of climate change at least 115 times from 2011 to 2015, often remarking on how cold weather casts doubt in his mind on the reality of harmful climate change. 

Others have used the same logic. New York Times reporter Kendra Pierre-Louis wrote in a December 28, 2017, article, “Politicians have tried to use cold snaps to prove a point before. Mr. Trump’s line of reasoning recalled a February day in 2015 when Senator James Inhofe, Republican of Oklahoma, brought a snowball to the Senate floor as evidence that the Earth was not warming.” Likewise, in a December 23, 2015, article, U.S. News & World Report staff writer Alan Neuhauser cited tweets or statements from at least five Republican senators and representatives who claimed that cold weather cast doubt on climate change trends.

Other politicians have taken on the logic of these claims. Following Trump’s statement, Democratic Representative Don Beyer offered his own response on Twitter on December 28, 2017, tweeting:

1: This isn’t how climate change works.

2: We weren’t paying trillions of dollars. You didn’t understand the Paris Agreement in June and you still don’t.

3: Climate Change is real. It is a serious threat to our children. You need people on your team who can explain this to you.
 

To find overall trends in climate, scientists look past localized variations in weather. In responding to President Trump’s tweet, many scientists explained that some variation in weather is normal. They also noted that one effect of climate change is a change in overall weather patterns, resulting in more frequent cold temperatures in some places. Rachel Becker, a reporter for The Verge, wrote about how scientists responded to President Trump, citing some of NASA’s online science education materials:

Cold weather can still happen as global temperatures rise. “The trip to a warmer world (climate change) will have plenty of extreme hot and cold weather,” NASA’s Climate Kids site patiently explains. We’ll just see more of those extremely hot days as the planet warms, according to the climate change tracking platform Climate Signals and scientist Michael Mann. He tweeted that record hot days are beating record cold days three to one.

Right now, a warm ridge of high-pressure air is hovering over the Western U.S., forcing the highway of winds that would normally bring cool, rainy weather to California up into Canada. That’s causing the extended warm, dry spell fueling California’s wildfires and the East Coast’s icy temperatures. When the jet stream plunges back down, it carries frigid air, “mainlining cold to the eastern half of the U.S.,” Brian Kahn writes for Earther.

Scientists led by Stanford’s Noah Diffenbaugh have studied this strange seesaw effect on temperatures across North America, where upward swings in winter temperatures in the west correspond with icy drops to the east. They found that this warm west / cold east combination is happening more often as the climate warms. “We have strong evidence that not only does it not invalidate global warming, but it’s actually very consistent with what we’d expect,” Diffenbaugh tells The Verge.
 

Cold weather, such as the extreme temperatures much of the U.S. experienced this winter, often brings questions about the validity of climate change. However, such questions often have more to do with political maneuvering than with climate science.
 

For Discussion:

  1. How much of the material in this reading was new to you, and how much was already familiar? Do you have any questions about what you read?
     
  2. Have you heard politicians or friends remark on the weather, relating it to climate change? What did you think?
     
  3. Why do you think some politicians use weather to attempt to deny climate change?
     
  4. The reading above includes several responses to President Trump’s tweet about climate change and cold temperatures. Which of the responses do you think make the best argument? Explain your reasoning.

 


 

Reading Two:
Climate, Science, and Statistics


Whether it is an idle joke from a passerby or a statement from a politician, using cold weather as a counterargument to global climate change represents a misunderstanding of science and statistics. The argument that climate change is not happening because one particular geographical area is experiencing cold weather relies on several fallacies.

The first of these fallacies is a statistical one: confusing one data point with an overall trend.

Two weeks of cold weather during January in the Midwestern United States may give us some information about the overall state of the climate, but it does not constitute proof that the Earth is not warming. Using just a few data points to assert a wider trend—particularly data points chosen for the purposes of supporting one’s argument—can lead to wildly inaccurate conclusions. In contrast, scientists and statisticians often try to use the largest data sample possible in order to draw a conclusion that is strongly supported by evidence. Scientists use the terms “trend” and “variation” to describe how, over time, data may vary dramatically, though the trend line clearly points in a particular direction. Using one data point such as a short-term weather event to make an argument about a larger trend is a failure to recognize the importance of gathering enough data to make a meaningful average and trend.

The second and related fallacy involves confusing “weather” with “climate.” The Environmental Protection Agency describes the difference between weather and climate this way:
 

Weather is the state of the atmosphere at any given time and place. Most of the weather that affects people, agriculture, and ecosystems takes place in the lower layer of the atmosphere. Familiar aspects of weather include temperature, precipitation, clouds, and wind that people experience throughout the course of a day. Severe weather conditions include hurricanes, tornadoes, blizzards, and droughts.               

Climate is the long-term average of the weather in a given place. While the weather can change in minutes or hours, a change in climate is something that develops over longer periods of decades to centuries. Climate is defined not only by average temperature and precipitation but also by the type, frequency, duration, and intensity of weather events such as heat waves, cold spells, storms, floods, and droughts.

While the concepts of climate and weather are often confused, it is important to understand the difference. For example, the eastern United States experienced a cold and snowy winter in 2014-2015, but this short-term regional weather phenomenon does not negate the long-term rise in national and global temperatures, sea level, or other climate indicators. It may be helpful to think about the difference between weather and climate with an analogy: weather influences what clothes you wear on a given day, while the climate where you live influences the entire wardrobe you buy.

 

Every winter in the Northern Hemisphere, scientists explain the difference between weather and climate as people wonder, how do snow and ice relate to the global climate change scientists have been talking about for decades? In a Q&A column, the popular science magazine Scientific American succinctly answered the question: Do snow and ice storms mean the climate is not warming?
 

Dear EarthTalk: Don’t all these huge snow and ice storms across the country mean that the globe isn’t really warming? I've never seen such a winter!
-- Mark Franklin, Helena, MT


On the surface it certainly can appear that way. But just because some of us are suffering through a particularly cold and snowy winter doesn’t refute the fact that the globe is warming as we continue to pump carbon dioxide and other greenhouse gases into the atmosphere.

According to the National Aeronautics and Space Administration (NASA), the 10 warmest years on record have occurred since 1997. And the National Atmospheric and Oceanographic Administration (NOAA) reports that recent decades have been the warmest since at least around 1000 AD, and that the warming we’ve seen since the late 19th century is unprecedented over the last 1,000 years.

“You can’t tell much about the climate or where it’s headed by focusing on a particularly frigid day, or season, or year, even,” writes Eoin O’Carroll of the Christian Science Monitor. “It’s all in the long-term trends,” concurs Dr. Gavin Schmidt, a climatologist at NASA’s Goddard Institute for Space Studies.

Most scientists agree that we need to differentiate between weather and climate. The NOAA defines climate as the average of weather over at least a 30-year period. So periodic aberrations—like the harsh winter storms ravaging the Southeast and other parts of the country this winter—do not call the science of human-induced global warming into question.
 

A third problem with using cold weather events to disprove climate change is that even relatively small changes in temperature can have dramatic effects on ecosystems. The fact that average overall global temperatures rise by a small amount does not mean that winter will cease to exist, or that we won’t continue to experience cold days. For an individual, the weather might feel not too different than before if it is just a few degrees warmer. Yet such small changes in average temperatures can nevertheless significantly alter conditions for life on the planet.

Climate scientists have agreed that keeping the trend of global temperature warming below 2 degrees Celsius is important for doing the least damage to ecosystems possible. Average global temperatures rising 2 degrees Celsius could cause enormous problems, including disruptions in our agricultural systems. NASA’s Bob Silberg explains in a June 29, 2016, article for NASA’s climate website:
 

The Paris Agreement, which delegates from 196 countries hammered out in December 2015, calls for holding the ongoing rise in global average temperature to “well below 2 °C above pre-industrial levels,” while “pursuing efforts to limit the temperature increase to 1.5 °C.” How much difference could that half-degree of wiggle room (or 0.9 degree on the Fahrenheit scale) possibly make in the real world? Quite a bit, it appears.

The European Geosciences Union published a study in April 2016 that examined the impact of a 1.5 degree Celsius vs. a 2.0 C temperature increase by the end of the century, given what we know so far about how climate works. It found that the jump from 1.5 to 2 degrees—a third more of an increase—raises the impact by about that same fraction, very roughly, on most of the phenomena the study covered. Heat waves would last around a third longer, rain storms would be about a third more intense, the increase in sea level would be approximately that much higher and the percentage of tropical coral reefs at risk of severe degradation would be roughly that much greater.

But in some cases, that extra increase in temperature makes things much more dire. At 1.5 C, the study found that tropical coral reefs stand a chance of adapting and reversing a portion of their die-off in the last half of the century. But at 2 C, the chance of recovery vanishes. Tropical corals are virtually wiped out by the year 2100.

With a 1.5 C rise in temperature, the Mediterranean area is forecast to have about 9 percent less fresh water available. At 2 C, that water deficit nearly doubles. So does the decrease in wheat and maize harvest in the tropics.

On a global scale, production of wheat and soy is forecast to increase with a 1.5 C temperature rise, partly because warming is favorable for farming in higher latitudes and partly because the added carbon dioxide in the atmosphere, which is largely responsible for the temperature increase, is thought to have a fertilization effect. But at 2 C, that advantage plummets by 700 percent for soy and disappears entirely for wheat.
 

While the effects of even a small rise in average global temperature can feel dire, climate scientists and concerned citizens share the information to encourage people to take climate change seriously and to join in efforts to address its causes.

 

For Discussion:
 

  1. How much of the material in this reading was new to you, and how much was already familiar? Do you have any questions about what you read?
     
  2. What is the difference between “weather” and “climate”? How does this distinction effect the debate about climate change?
     
  3. Why do climate scientists want global leaders to agree to keep the world’s average temperature increase under 2 degrees Celsius? What could be the impact of such a rise in temperature?
     
  4. Knowing that just a small difference in average global temperatures may have significant and negative consequences, how do you think that people should respond?
     

 

– Research assistance provided by Ryan Leitner.