An international study in Nature Communications co-authored by researchers from the ARC Centre of Excellence for Climate Extremes (CLEX) and the Institute of Marine and Antarctic Studies (IMAS) reveals globally marine heatwaves have increased over the past century in number, length and intensity as a direct result of warming oceans.

From 1925-2016, the study found the frequency of marine heatwaves had increased on average by 34% and the length of each heatwave had increased by 17%. Together this led to a 54% increase in the number of marine heatwave days every year.

"Our research also found that from 1982 there was a noticeable acceleration of the trend in marine heatwaves," said lead author, Dr Eric Oliver from Dalhousie University, Canada.

"While some of us may enjoy the warmer waters when we go swimming, these heatwaves have significant impacts on ecosystems, biodiversity, fisheries, tourism and aquaculture. There are often profound economic consequences that go hand in hand with these events."

Some recent examples show just how significant marine heatwave events can be.

In 2011, Western Australia saw a marine heatwave that shifted ecosystems from being dominated by kelp to being dominated by seaweed. That shift remained even after water temperatures returned to normal.

In 2012, a marine heatwave in the Gulf of Maine led to an increase in lobsters but a crash in prices that seriously hurt the industry's profits.

Persistent warm water in the north Pacific from 2014-2016 led to fishery closures, mass strandings of marine mammals and harmful algal blooms along coastlines. That heatwave even changed large-scale weather patterns in the Pacific Northwest.

More recently still, Tasmania's intense marine heatwave in 2016 led to disease outbreaks and slowing in growth rates across aquaculture industries.

This year has been “anything but ordinary” according to the latest data released by the National Oceanic and Atmospheric Administration (NOAA). In the first three months of 2018, the United States has seen three climate and weather disasters each resulting in more than $1 billion in damages.

Two of the four nor’easters to hit the central and eastern U.S. during a one month period resulted in record snowfall and more than a billion dollars in losses each. Millions were without power and hundreds of flights were grounded. Multiple deaths were reported across Connecticut, Maryland, Massachusetts, New York, Pennsylvania, Rhode Island, and Virginia. . . .

. . .scientists know that climate change is making nor’easters more powerful.

Nor’easters form when warm ocean air converges with cold terrestrial air. They are more powerful in the winter when the temperature difference is greatest. Climate change is making the temperature contrast even more pronounced, both by warming the Atlantic and by distorting the jet stream, allowing frigid Arctic air to reach further south. Rising temperatures in the Arctic are responsible for reshaping the jet stream.

Like with summertime hurricanes, winter nor’easters start in the ocean. And with warmer waters, these storms become more intense. According to Accuweather, this year’s series of devastating nor’easters spent more time forming over the ocean, giving them a chance to increase in strength by absorbing more of the warmer ocean temperatures.

The Australian Bureau of Meteorology's latest climate outlook, issued today, suggests the above-average warmth of April is likely to extend into May and, for parts of the south, potentially into winter.

The outlooks for May temperatures show that both days and nights are likely to be warmer than average for much of Australia. Only north-east Queensland is likely to miss out on warmer temperatures, with no strong push there towards warmer or cooler conditions.

The unseasonable warmth, which has broken records in Adelaide and Sydney, appears to be driven by high ocean temperatures, and weaker westerly winds and much lower than average soil moisture across southern Australia.

Seems some authority disagrees.

Link.