Ah, fresh cookies from the oven! Who doesn't love them…except when things go wrong. When cookies burn it's easy to guess that heat probably played a role. But what if the cookies are too flat or very dry and crumbly? Could the baking powder be too old? Was the batter over-stirred? Similar to a batch of cookies, an extreme weather event is the result of all the conditions in the atmosphere. Lately, after an extreme heat wave or storm, many people have begun asking what influence climate change may have had. Climate change is causing more extreme weather, but it's been hard to quantify its contribution to any individual event. Recent scientific advances make that calculation possible for some types of events. Confidence is highest for extreme weather events that are connected to temperature. Heat waves are like burnt cookies.
A warmer climate is a primary factor in an observed increase in heat waves. Heavy downpours and drought are more like the flat or dry batch of cookies. It's trickier to determine how much any factor played a role. To study the cookies you might run a series of experiments in your kitchen, but scientists can't just cook up extreme weather. Instead, scientists use three tools: their understanding of the physical climate, past observations of the frequency and intensity of extreme weather events, and climate models that compare extreme weather in a world with and without climate change. When the clues line up, scientists can be confident in their answer. Unlike cookies, the recipe for an extreme weather event isn't always the same, but understanding how all the ingredients come together is critical to protecting communities from a changing climate.