Increased probability of floods means that on any given day the chance of a flood or heavy rains is higher in some places than it would have been without climate change. Over the course of years this guarantees there will be more extreme events.
The extreme weather the world has seen is part of a larger trend, he said. "The world is warming up ... It's warming for sure and science is very confident that most of the warming is due to human causes."
Every time we burn fossil fuels like coal, oil and natural gas, Sommerville said, we emit carbon dioxide into the atmosphere. Now, climate scientists see "the changed odds, the loaded dice that favors more extreme events and more high temperature records being broken," he said.
The decade that just ended saw nine of the 10 warmest years on record, and warmer temperatures mean more moisture in the air. That moisture can fall as torrential, flooding rains in the summertime or blizzards in the winter.
"Because the whole water cycle speeds up in a warming world, there's more water in the atmosphere today than there was a few years ago on average, and you're seeing a lot of that in the heavy rains and floods for example in Australia," Sommervile said.