After the Louisiana floods in the summer of 2016, a team of scientists estimated that due to climate change, such an event is at least 40 percent more likely to occur than it was in the preindustrial past, and that the rains were about 10 percent more intense than they would have been without recent warming.
After superstorm Sandy in 2012, researchers found that – although the storm was influenced by many factors other than climate change – warmer-than-usual sea surface temperatures were involved. Because water expands as it warms, the storm was riding on sea levels that were higher by about 19 centimeters (7.5 inches) because of global warming. “It is quite possible that the subways and tunnels might not have flooded without the warming-induced increases in sea level and in storm intensity and size,” wrote the authors of the study, which was published in Nature Climate Change.
The effects of climate change on the intensity of a weather event, such as the amount of precipitation, can be small, says Kevin Trenberth, senior scientist in the Climate Analysis Section at the National Center for Atmospheric Research (NCAR) and a lead author of that study. But often those effects are enough to push a weather event over the threshold that makes it damaging or catastrophic. “In general, there’s about 6 or 7 percent more moisture over the oceans,” Dr. Trenberth says. “So when it rains, it tends to rain harder by about that amount,” or a bit more as storms get invigorated.