The facts of climate change are widely reported. NASA notes, for example, that with a two-degree-Celsius increase in global temperatures, as compared with a 1.5-degree-C increase, about 61 million more people living in urban areas around the world will be exposed to severe drought. In addition, the U.S. alone could lose 2.3 percent of its gross domestic product for each degree-C increase in global warming.
The problem with communicating these numbers, however, is that many people balk when confronting them. Math anxiety—the experience of tension, fear or apprehension when confronting mathematical problems—and innumeracy—the inability to understand and employ numerical concepts—are both quite common. (For the numerically curious: about a third of working-age Americans struggle with simple numeric processes.)
This reality creates a significant challenge when discussing climate change and other complex topics. If people get anxious when they see numbers, should you use them to give perspective on climate science? Or will that cause people to turn away? In a series of studies, we set out to answer those questions. Our findings reveal that numbers have persuasive power—but they need to be employed with care to compel action. The lessons we learned can help not only climate advocates but anyone hoping to draw on data to sway their audience.
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We first conducted two studies using field data from social media sites in late 2022. We gathered about eight million messages from climate scientists on Twitter (now X) and more than 17,000 messages from a climate change subreddit on Reddit; that is, an online community focused on climate change. Our collection of messages excluded irrelevant text, such as a Twitter handle that contained numbers. Next, we did a simple classification of messages by calling them numeric if they included at least one Arabic integer. For example, messages containing “9” or “27” were numeric. Otherwise, they were classified as nonnumeric.
Just one in four tweets and one in three Reddit posts were numeric. But those messages were shared significantly more often than the nonnumeric tweets and posts. For instance, people retweeted numeric tweets 16.9 percent more often and upvoted Reddit posts featuring numbers 31.7 percent more often. People regarded these posts and tweets as compelling enough to want to communicate them to others.
We also found that on Twitter, numeric posts had fewer “likes” on average than nonnumeric posts. We think that providing numeric evidence may have clarified the dismaying magnitude of climate threats, making it difficult for people to like a tweet (which involves pressing a heart icon) because they felt worse about the message.
Then we conducted an experiment to see if numbers caused people to think and feel differently about climate science. We recruited 212 participants from an online research platform and presented each with 20 Tweets to review, mimicking the experience of scrolling through messages on social media. Every participant saw a different mix of messages. All of the tweets focused on climate change consequences (specifically its monetary costs or impacts on the environment and on humans or other species), and each fell into one of four categories. Some tweets expressed climate change consequences in precise Arabic numerals (such as “Each year, Antarctica loses 151 billion tons of ice”). Some presented such consequences with imprecise, quantity-related language ( “billions of tons of ice). Others presented consequences without numbers or quantitative language (“a lot of ice”). And still others contained numbers unrelated to the climate change outcomes (“a lot of ice, according to COP27”).
Ultimately, participants reported that they would be more likely to share and want to find out more about messages with precise numeric information on climate change consequences compared with messages in the other categories. They also trusted the messages more and thought the message sender was more likely to be an expert. These effects were stronger among people who were good at math, who preferred receiving numeric information and who were more liberal. Numbers did not have negative effects on other participants, however. People who were more conservative, for example, also thought that senders of numeric messages were more likely to be experts than the authors of tweets that didn’t use precise Arabic numerals to describe climate consequences.
Why is mathematical information so persuasive even when it makes many people uncomfortable? Despite high rates of innumeracy, there are reasons to think that people may not disengage when they receive numbers. First, multiple past studies show that people often prefer getting numerical details over purely verbal communication. People also trust messages provided by medical professionals or journalists more when that communication includes numbers than when it does not. The use of specific numbers signals expertise to readers.
But trade-offs exist. Given people’s anxiety about math and level of mathematical ability, there is an upper limit when relaying these kinds of details. In past research, one of us (Peters) found that people find numbers helpful, so long as there aren’t too many of them. No hard-and-fast rule suggests how many is too many—it depends on the complexity of the topic, people’s familiarity with the subject and their overall numeracy. Communicators therefore need to know and attend to their audience: if a speaker sees someone’s eyes glazing over, for example, it’s a sign to back off on the numbers.
In addition to the possibility of being overwhelmed by numbers, their persuasive power could have consequences that communicators need to consider. Based on our most recent findings, for example, we argue that balancing the message may be especially important to climate action. Our study participants reported more negative feelings about the tweets containing numeric consequences of climate change. To be clear, we do not think this reflected math anxiety. Instead—as with the tweets that received fewer likesbut were still widely shared—we think these tweets elicited negative emotions because the numerically precise messages were stronger in conveying the devastating consequences of climate change.
It’s possible that even if people share numeric climate science facts more than nonnumeric statements, despair or hopelessness may stop them from taking further action. Think about counteracting this response by talking about feasible solutions to the problem, too. If you can suggest actions that people feel they can carry through, that could counterbalance the negative feelings that arise when they consider climate change’s consequences.
So whether you’re an environmentalist seeking to communicate more effectively over social media or looking for strategies to persuade family over the Thanksgiving dinner table, there are a few lessons here. Find the key numerical data and share that. Think strategically about data presentation. (Numbers and text with visuals are often helpful when making risk assessments, for example.) When talking about climate change, include some proposed action. Given that past work suggests that sharing numbers builds trust, your readers or listeners may be more likely to follow your recommendations. When used wisely, numbers can help transform anxiety into action, which could help turn the tide in our fight against climate change.
Are you a scientist who specializes in neuroscience, cognitive science or psychology? And have you read a recent peer-reviewed paper that you would like to write about for Mind Matters? Please send suggestions to Scientific American’s Mind Matters editor Daisy Yuhas at dyuhas@sciam.com.
This is an opinion and analysis article, and the views expressed by the author or authors are not necessarily those of Scientific American.