To say that climate change is responsible for the recent string of tropical storms that have come into existence throughout the Atlantic Ocean would be an obvious inaccuracy. Tropical storms, as well as other devastating natural disasters such as tornadoes, earthquakes, blizzards, and so on – they have all been recognized as parts of natural global phenomena for as long as anyone can remember. So, to ask if climate change is responsible for the likes of Hurricane Irma, the immediate answer would be no. However, if you were to ask if climate change caused Irma‘s advanced destructive capability, that would be a whole other animal to address. And many people would answer with at least a tenuous yes.
In most cases, hurricanes are caused by excess water vapor rising off the surface of the ocean. This is why hurricanes typically develop in lower latitudes and typically subside once they travel far enough north; the warmer water that evaporates is a better catalyst for storm systems than cooler water. The process by which a hurricane develops involves the water vapor warming the surrounding areas and returning to a condensed form when the latent heat is released in the upper atmosphere – in the form of clouds and rain. In most storm systems, the presence of any substantial wind shear will drive off some of the latent heat and reduce the intensity of a storm dramatically. However, when that wind shear is absent, heat builds up in a storm and can cause a low-pressure system to form around it. Any wind that is present in this low-pressure system begins to spiral inward, building at an exponential rate. The subsequent buildup of wind in the system causes more water to evaporate off the surface of the ocean, contributing more heat to the system and thereby developing more rain and more clouds in the process. And boom, you have the start of a hurricane.
Now, consider the changes in climate in recent years. Global warming has contributed to higher sea levels and an increased average oceanic temperature of about 1.5 degrees Fahrenheit over the last 100 years. I know that doesn’t sound like a lot, but consider how much water is covering the planet’s surface and how much heat would be required to accomplish that. This rise in temperature would only make it that much easier for water to evaporate off the ocean’s surface and create the beginning of a scenario in which a hurricane becomes very likely. And because there is now more water (thanks to rising sea levels) to contribute this water vapor to a storm system, the ability for a hurricane to develop more quickly and with greater power behind it becomes much easier.
The fact that hurricanes develop faster and easier than ever before is undeniable in any case. Experts say that hurricanes are generally capable of reaching category 3 levels about 9 hours quicker than they might have been 30 years ago. And the fact that more water vapor is being used to fuel these storms is one of the reasons why Hurricane Harvey was able to set a record for rainfall on the continental United States during the span of a single weather event. While many experts don’t necessarily find an irrefutable, conclusive correlation between the increasingly damaging hurricanes of this year and human-made climate changes around the world, they will say that the data makes a fairly strong suggestion toward that conclusion.