Climate warming is changing the weather like steroids change a baseball player, a leading expert told a conference of insurance executives.Roger Grenier, senior vice-president of the global resilience practice at catastrophe modelling firm AIR Worldwide, quoted the oft-repeated analogy made popular in the Bulletin of the American Meteorological Society.Speaking at the Bermuda Reinsurance Conference, presented by S&P Global Ratings, at the Hamilton Princess Hotel and Beach Club, he said steroids, or climate change, can’t be tied to a particular occurrence — a home run or an extreme weather event, for example — but they make such events more likely.In the case of climate, Dr Grenier said changes in the mean temperature and/or variability greatly increase the probability of extreme events.Today, the impact of climate change is felt across all lines of re/insurance business.Interest in the topic is reflected in the fact that AIR’s 2017 paper “Climate Change Impacts on Extreme Weather”, is the most downloaded piece of content the company has produced.Some modern hurricane trends are developing. Dr Grenier, who earned a PhD in engineering from North Carolina State University, said: “Storms are reaching their maximum intensity in higher latitudes. “They have moved north 50 kilometres [31 miles] over the last 12 years. That is the difference between Cape Hatteras, North Carolina and Virginia Beach.“We also see that storms are slowing down and they are getting stronger.” After his presentation, saying that climate change is “definitely real”, Dr Grenier said the physics of it have been understood for some 150 years, but it was only in the last 75 years that data began to be collected in a manner that allowed scientists to quantify the carbon dioxide that was accumulating in the atmosphere.He said: “We knew there was an increase in carbon dioxide in the atmosphere, and we always understood that it would lead to warming — the greenhouse effect.”Over time there developed greater confidence that the accumulation was being caused by human activity, according to Dr Grenier. He said: “That is probably the biggest change that has occurred, as it created an understanding that climate change was being caused by humans. Now, it is possible to change behaviour, whereas if it was naturally occurring, it’s not something that we can do much about.“The question is whether it’s too late to make any meaningful changes because a lot of the warming is already baked into the atmosphere. It’s not an easy thing to reverse.”He said his organisation’s role is to help inform debates. “In our world, we don’t advocate,” he said.However, Dr Grenier said any attempt to address the impact of climate change would “probably require a multitude of changes in behaviour”.He added: “There are things that individuals can do — drive less, eat more plant-based foods — but it also requires large-scale policy changes that will drive bigger impacts, things like accelerated renewable energy, that is one example of a practical thing that can be done, but at the other end, a carbon tax could drive behaviour.”Bermuda residents are accustomed to experiencing extreme weather events, but Dr Grenier said he couldn’t assist with any forecasting in that regard.“For events that are rare to begin with, like hurricanes, the overall frequency of events will decrease, but they’ll be more severe,” he said. “That’s a broad-brush statement, but I can’t with any confidence say how Bermuda will be affected.“Every March, we get the forecasts for the hurricane season, but they don’t make any predictions about how many hurricanes will make landfall, or where. “There is no predictive ability even a few months in advance, so we’re not at the stage where we can predict what will happen in 20 years.” He added: “Buy the roller shutters, for sure, and hope for the best.”