Study author James Kossin of the National Oceanic and Atmospheric Administration says Harvey is a great example of what he found.
The U.S. National Hurricane Center said Tropical Storm Aletta was centered about 350 miles (565 kilometers) south-southwest of Manzanillo, Mexico, Wednesday morning.
These two trends ought to work in tandem to make today's storms much worse rainmakers.
And when it came to the storms' travel over land, the slowdown in some cases was even more pronounced than it was over the oceans or in general. That means a storm that may already hold more moisture will have time to drop more of it in each spot.More news: Muhammad Ali: President Trump mulls draft dodging pardon
And that was before slowpoke Harvey hit a year ago.
Harvey dumped 60.58 inches of rain in Nederland, Texas, from August 24 to September 1. "And that has effects on circulation - typically slows it down".
Kossin acknowledged problems with pre-1970s data but said that most of it deals with how strong storms are.
In a warming world where atmospheric circulations are expected to change, the atmospheric circulation that drives tropical cyclone movement is expected to weaken. However, scientists have struggled to isolate the impacts of climate change on the characteristics of extreme weather events.More news: Bad News for Democrats Seeking Reelection? McConnell Cancels Most of August Recess
"These trends are nearly certainly increasing local rainfall totals and freshwater flooding", Kossin said, "which is associated with very high mortality risk".
The result is more rainfall and more damage to buildings as hurricanes hover over population centers for longer periods of time.
Kossin admits that there are probably both natural and manmade factors influencing the slowing of storms and recommends further studies using climate models to determine how much greenhouse gas emissions are responsible for affecting the storms' speeds.
He said beyond the changes in regularity and intensity of cyclones, their very "behaviour" was being affected by climate change. "We'll need more formal attribution studies to disentangle these factors".More news: IHOP to IHOB name change 'dumbest' move ever, brand experts warn