Season's 1st tropical storm forms in eastern Pacific

Season's 1st tropical storm forms in eastern Pacific

With polar regions warming faster than other parts of the globe, that is altering pressure gradients, reducing the winds that push these storms.

Looking at data since 1949, a government climate scientist calculates that storms in the last few years are moving about 10 percent slower globally than they were 60 years ago.

In the last 70 years the storms have slowed by ten per cent.

At the same time, related research published just last month suggests that warming temperatures from climate change will slow storms more in the future.

Scientists have been predicting that cyclones will move more slowly as the world warms and tropical air circulation patterns-which ferry storms from one place to another-weaken.

Kossin's work was based on details of nearly 70 years' worth of storms, but he made no attempt to determine what was causing the slowdown.

According to Kossin's study, combining the additional water vapor available in the atmosphere from 1 degree Celsius of warming -essentially where we are now - with a 10% slowdown from tropical cyclones that he observed would double the local rainfall and flooding impacts.

Dr Christina Patricola, from the Climate and Ecosystems Sciences Division at University California, Davis, says the findings raise several questions, especially regarding "stalled" tropical cyclones.

"These trends are nearly certainly increasing local rainfall totals and freshwater flooding, which is associated with very high mortality risk", he said. Rainfall, on average, increased 24 percent. "That has serious implications for inland flooding and urban infrastructure".

Dr Kossin said more rain was also falling during cyclones, and there was evidence that tropical cyclones were migrating more towards the poles. And there are limits to each approach.

But both scientists say the importance is in the bigger picture. "And, unfortunately, this signal would point to more freshwater flooding".