Howard Kunreuther, Wharton Risk Management and Decision Processes Center, University of Pennsylvania
Paul Slovic, Decision Research and the University of Oregon
The COVID-19 pandemic has introduced or reintroduced many people to the concept of an exponential curve, in which a quantity grows at an increasing rate over time. Most people, including leaders and policymakers understand a pattern of smooth, linear growth but have a harder time imagining exponential growth. With respect to COVID-19 you can have two cases of coronavirus tomorrow, four on the third day, hundreds after the seventh day and thousands soon after — a situation that’s challenging to anticipate and manage. It’s also characterizes CO2 emissions today and its impact on climate change. The silver lining associated with the coronavirus pandemic is that is teaching us a valuable lesson about the perils of ignoring destructive processes that increase exponentially.
More than 40 years ago a series of pioneering psychological experiments by Willem Wagenaar and his colleagues demonstrated that the human mind does not easily grasp the explosive nature of exponential growth but these findings have not received the attention they deserve. The deceptive nature of exponential growth was conveyed nicely in a piece on March 10 2020 in the Washington Post by Megan McArdle. She posed a brain teaser associated with lily pads in a pond. More specifically, if the number of lily pads doubled from one day to the next and the pond is covered completely on Day 48, people do not grasp that after 40 days of exponential growth, lily pads would cover only 1/256th (0.4 percent) of the pond. After 47 days, the pond still would only be half covered.
Turning to COVID-19, in the first two months of 2020, the general public, key decision-makers at the national, state and local levels in the United States were not concerned with the coronavirus and did not give much thought to the possibility of a pandemic affecting residents in our country. At the end of February there were only 70 individuals who had become ill from COVID-19 and the first fatality was reported on Feb 29. One of the reasons that the general public and key decision makers were not paying attention to the coronavirus in January or February is that they failed to appreciate the concept of exponential growth. Figure 1 depicts the exponential growth of residents contracting and dying from COVID-19 in New York City from March through April. That’s the nature of pandemics and epidemiologists understand this.
Aside from the coronavirus pandemic, the biggest, most destructive exponential growth processes are those associated with global climate change that will lead to more severe heat waves, greater sea level rise and, more intense hurricanes in the coming years, unless we take strong measures now to reduce them. Consider the following empirical studies:
- A 2013 analysis in 136 major coastal cities around the world revealed that sea level rise (SLR) of 20 cm (7.9 inches) by 2050 will cause the average annual flood losses in those cities to increase to $1.2 trillion that year from $52 billion in 2005.
- Most of the United States could see 20 to 30 more days annually with maximum temperatures higher than 90 degrees, with the Southeast potentially experiencing 40 to 50 more such days. This extreme heat poses serious health risks to residents in the area notably the very young and the elderly and those living in urban areas.
- There are likely to be more severe wildfires as temperatures rise and the increased possibility of long dry spells due to climate change. The drought experienced by California from December 2011 to March 2019 contributed to extensive wildfire damage that is likely to increase significantly in the future.
Recognizing that dealing with the serious health concerns and economic impacts of the coronavirus must be everyone’s top priority, there is a vital lesson from contemplating the exponential growth of COVID-19 illnesses and fatalities. The curve looks and feels innocent and benign, and easy to ignore in its early stages. But suddenly, and sooner than you expect, it takes off in a torrent of harm that can be overwhelming. We need to attend to the serious problems caused by climate change and the need to reduce CO2 emissions now, before it is too late.