Trying to figure out what impacts human-caused climate change has on the development of extreme weather, including tropical storms, is cutting-edge research for a team of scientists who talked Monday about their difficult work.

There are just so many naturally occurring climate factors at play in the development of extreme weather that it’s become very difficult to show what, if any, impact climate change has had.

The scientists talked about some of these challenges while releasing their third report that attempts to attribute how much human-caused climate change contributed to 16 extreme weather events around the world last year.

“Extreme (weather) events are very complex and have multiple causes,” said Thomas Karl, director of the National Oceanic and Atmospheric Administration’s National Climatic Data Center. “It’s not ever a single factor that is responsible for these extremes that we see.”

Published by the Bulletin of the American Meteorological Society’s September edition, the report pulls together 20 different research teams to study 16 events around the world from drought to floods.

This research of attempting to tease out human-caused climate change impacts from naturally occurring weather abnormalities is a relatively new pursuit, Karl said.

However, it adds value to climate research because, as advances are made by studying the past, it will help improve forecasts in the future.

The 16 weather events were chosen by the scientists who did the individual studies, many times because the extreme weather occurred in their “backyard,” he explained.

The complexity of each extreme weather event, and the numerous variables each event has, means that the results of the 20 studies gave a variety of results.

With the California drought last year, three separate studies didn’t find any conclusive evidence of human-caused climate change playing a role.

“A clear picture of how long-term climate change impacted the California drought has yet to emerge,” said Stephanie Herring, with NOAA’s National Climatic Data Center. “This is really hard, cutting-edge research.”

However, five studies done in Australia and New Zealand all indicated human-caused climate change contributed to a measurable increase in high temperatures.

“Nine analyses of extreme heat events overwhelmingly showed that human-caused climate change substantially influenced all of these events,” Herring said.

Analyses of three storms, including a South Dakota blizzard, a cyclone in northwestern Europe and extreme snowfall in the Pyrenees Mountains, didn’t find any role for human-caused climate change, she said.

Currently, it’s easier to tease out climate change factors from extreme temperature events than it is from other extreme weather events like drought and storms, Karl said.

“As models, data and methods improve, you could end up with new results in future studies and that’s how science evolves,” Karl said.