How Does A Tiny Change in Climate Become Fatal?

Michael Oppenheimer explains the significance of considering social factors and scientific factors when faced with extreme weather events at Columbia University’s Correlated Extremes Conference.

The Intergovernmental Panel on Climate Change, the Paris Agreement, the Green New Deal, and many other climate change reports, proposals, and policies assert that if we allow the Earth to warm more than two degrees Celsius, we’re doomed.

But when I step outside in the morning, I couldn’t tell you the difference between 20°C (68°F) and 22°C (71.6°F). How can such a tiny change in climate mean doomsday? By increasing the average, we increase the extremes: heat waves, cold spells, hurricanes, droughts, floods, and more.

In May, I attended Columbia University’s Workshop on Correlated Extremes, which brought researchers and experts from around the world to Columbia to discuss how extreme weather events are connected. According to the researchers at the workshop, as these occurrences become worse and more frequent, we start to see extreme weather events occurring simultaneously, back to back, or in several places at once. Every presenter I watched agreed that the impacts of these events on public health, agriculture, food, and security can be devastating.

Opening night at the Workshop on Correlated Extremes at Columbia University. (From left to right: Adam Sobel (Columbia), Michael Oppenheimer (Princeton), Sarah Perkins-Kirkpatrick (UNSW), and Kate Marvel (NASA GISS)

During the record-breaking North American Cold Wave last January, I was checking out at a local convenience store when the cashier asked me, “What do you think of this global warming thing?”

As a student at Boston University studying Environmental Analysis & Policy, I couldn’t help but say that the cold spell was caused by climate change—the warming of the North Pole caused the polar vortex to weaken, letting cold air slip through to where we were in Boston and all across North America. What followed was a great conversation during which the cashier went from asking if the government controls the weather to considering the idea that weather is a natural process affected by climate, which humans can’t control, but can impact.

Hearing that cashier’s take on a cold January evening reminded me that humans don’t perceive climate, we perceive weather. Climate refers to the general temperature and precipitation trends in an area over years, decades, and centuries, whereas weather refers to the temperature and precipitation conditions in an area at a specific hour, day, or week. This distinction explains why a cold spell in North America doesn’t mean the climate is cooling.

Weather and climate are different. Credit: Department of Environmental Protection of the State of New Jersey

But climate and weather are correlated. Small changes in climate make variations in weather more extreme. We don’t experience an evenly spread couple of degrees of warming every day. We experience much hotter hot days, much colder cold days, much wetter forests, much drier deserts, much stronger storms, and many more tiny changes that, taken together, make climate change cause for concern.

That January cold wave alone led to billions of dollars in damage, countless frostbite injuries, and over 21 casualties, many of whom were homeless people with nowhere to turn.

But afterwards, temperatures in some areas warmed up to temperatures as high as 80°F within two to three days, immediately switching from extreme cold to extreme heat (compared to normal winter weather). While the warmer temperatures brought some well-deserved relief to these communities, the record-breaking speed of the warm-up also caused pipes to burst and flooding from fast-melting snow.

United States temperature analysis on January 31, 2019. Record lows across the Midwest. Credit: National Weather Service Weather Prediction Center

Researchers at the Workshop on Correlated Extremes would likely describe this phenomenon as a sequential event: two extreme events occurring back to back. In this case—and many other cases—the combined impact of two back to back extremes is worse than the sum of their parts. A 55°F day in February on its own would cause issues, but following a historic cold wave, the problems multiply. The combinations are endless: a hurricane followed by heavy rainfall equals unprecedented flooding, a heat wave followed by a dip in temperature plus a second heat wave leaves no time for non air-conditioned buildings to cool off, warm wet weather in early spring followed by a cold snowstorm causes plants to be tricked into starting to grow, only to get killed off instantly, and the list goes on.

In addition to sequential events, climate change is causing more compound events and concurrent events. Compound events refer to two extremes occurring at once—hot and humid, hot and dry, cold and snow, etc. Concurrent events describe a particular extreme occurring in many areas—droughts, floods, heat waves, or other similar events in several regions at once. Compound events can multiply the impact of each extreme event, and concurrent events can lead to an event having a more wide scale impact. For example, if half the farms in America concurrently had a drought, the resulting widespread crop failures could upend the food market.

NASA’s Dr. Alexander Ruane presents three types of correlated extremes at Columbia University’s workshop.

Back at the Workshop, researchers shared the impacts of these increasingly frequent correlated extremes on their sectors and the current lack of preparation for them.

Steve Bowen, Head of Catastrophe Insight at the insurance company Aon, revealed that floods are not covered by standard home insurance, and during Hurricane Harvey (which caused $125 billion in damages), less than 20% of homes had a national flood insurance program in place. Dr. Jeremy Hess, Associate Professor of Emergency Medicine and Associate Professor of Environmental and Occupational Health Sciences at the University of Washington, shared that agriculture, water, and sanitation are all key factors for public health, and at a time when correlated extremes put those factors at huge risk, the United States has the worst healthcare access out of all 36 Organisation for Economic Co-operation and Development (OECD) countries. Dr. Alexander Ruane, a Research Physical Scientist at the NASA Goddard Institute for Space Studies and a specialist in agriculture, demonstrated that when correlated extremes disrupt the growing season as discussed above, food insecurity is exacerbated, leading to increased food prices, hunger, malnutrition, and casualties that communities in America and around the world are not equipped to handle.

University of Washington’s Dr. Jeremy Hess explains the effects of correlated extremes on human health at Columbia University’s workshop.

As a college student, climate change is often framed to me as my generation’s problem, one with which we’ll have to grapple decades down the line.

It will certainly be much worse in fifty years, but as that freezing January night reminded me: It’s already here, and it’s affecting all of us. Correlated extremes are on the rise, and each one can rack up billions of dollars in damages and often cause a serious death toll.

The key takeaway of each workshop presentation was clear: as we look ahead, we need to do more than just prepare for heat waves, hurricanes, floods, or droughts. We need to prepare for combinations of these events, and we need to do it now. These researchers are hard at work analyzing the ways in which these different combinations of events could create greater damage than the sum of their parts—and now that extremes are the norm, communities need to put this research into action.