Severe storms have pounded the Detroit area with flooding, damaging winds, downed trees and power outages, but Michigan is hardly alone. Across the country, Americans have watched communities confront extreme rainfall, tornado outbreaks, dangerous heat, drought, wildfires and hurricanes — sometimes seemingly one disaster after another. It can feel as though something about the weather itself has changed. In important ways, it has.
There isn’t one explanation for every flood, tornado, hurricane or wildfire. But the environment in which those events develop is changing. The planet is warmer than it was in the past, and that changes the basic conditions surrounding weather systems. For every 1 degree Celsius — about 1.8 degrees Fahrenheit — that the atmosphere warms, it can hold approximately 7% more water vapor. That doesn’t mean it rains everywhere all the time. It means that when the atmospheric ingredients come together to produce a major rainstorm, there can be more moisture available for that storm to release.
Warmer oceans matter too. They’re enormous reservoirs of heat and moisture, and additional ocean heat can increase evaporation and provide more energy and moisture to certain storms. The oceans have absorbed about 90% of the excess heat from planetary warming. At the same time, higher temperatures can pull moisture more quickly from soils and vegetation, worsening dry conditions in some regions and creating environments more favorable for wildfires. The result can seem contradictory: one part of the country can be struggling with flooding while another is dealing with extreme heat, drought or fire.
The extremes are increasingly visible in U.S. weather records. June brought 374 preliminary tornado reports across the Midwest, with Illinois, Indiana and Missouri setting records for June tornado activity. Meanwhile, the West and Southwest experienced their hottest January-through-June period in 132 years of records while receiving less than 70% of their normal precipitation. Climate change does not mean every tornado, flood or wildfire was caused by global warming — and scientists have considerably more confidence about its connection to extreme heat and heavy rainfall than to changes in tornado frequency. Individual weather events, however, are now occurring against a warmer climatic backdrop.
The Science Behind the Extremes
Scientists describe part of what is happening as an intensification of the water cycle. A warmer atmosphere can draw more moisture from Earth’s surface, contributing to drying in some places while also carrying more water vapor that can later fall as heavy precipitation somewhere else. In other words, floods and droughts aren’t necessarily opposite climate signals. A warming planet can contribute to conditions that make both more severe.
Earth hasn’t suddenly become a different planet, but the atmosphere and oceans surrounding us have measurably changed. The weather we experience still depends on natural patterns that determine whether a community gets a thunderstorm, hurricane, tornado or dry spell. But those events are now unfolding against a different backdrop — warmer oceans, more moisture in the atmosphere and higher temperatures over land. So if it seems as though something about our weather has changed, there is science behind that feeling. The planet’s weather systems are still doing what they have always done, but the environment in which they operate is changing.
