Why didn’t the good people of Houston start campaigning against global heating after Hurricane Harvey in 2017 left a third of their city underwater?

Why didn’t the citizens of the Philippines demand that their country end its heavy reliance on burning coal for power after Typhoon Haiyan killed at least 6,300 of them in 2013?

Why weren’t the survivors in the state of Orissa up in arms about India’s greenhouse gas emissions after the most intense cyclone in history killed 15,000 of them in 1999?

Well, partly because there were no data proving that the warming was making the tropical storms worse. Until now — and as if to celebrate its belated arrival, here comes another monster storm.

Last Sunday and Monday, Supercyclone Amphan spun up quickly over the warm waters of the Bay of Bengal, going from nothing much to a Category 5 tropical storm and adding 175 kph to its sustained wind speed in only 36 hours. India's meteorologists were predicting that the surge of water when it hit the coast could be as high as 3 to 5 meters.

People living around the Bay of Bengal know that storms are getting worse. So do people living around the Caribbean, on the U.S. eastern seaboard, and at the western end of "typhoon alley" (the Philippines, China, Korea and Japan). But they needed hard evidence, and now they have it.

A study by researchers at the National Oceanic and Atmospheric Administration and the University of Wisconsin at Madison, published Monday in the Proceedings of the (U.S.) National Academy of Sciences, confirms that there is a direct link between warmer oceans, more water vapor in the air and bigger tropical storms.

Not more storms, but much bigger. In fact, the likelihood that any given tropical storm will grow into a Category 3 or higher hurricane (or the equivalent in terms of cyclones and typhoons) is rising by 8 percent per decade.

Could it just be natural variation? James Kossin, lead author of the new study, doesn’t think so: “We have high confidence that there is a human fingerprint on these changes.” The data extend over four decades, which means the number of Category 3 or bigger hurricanes has grown by a third since 1980. It can only get worse, as will almost every other climate impact.

The average global temperature now is 1.1 degrees Celsius above the pre-industrial average, but there is already enough carbon dioxide in the air to give us another half degree of warming when it delivers its final load. The point will come, as with most of the other climate changes, when the local environment is no longer compatible with a normal human lifestyle.

For the 500 million people who live around the Bay of Bengal, the world’s biggest bay, the breaking point may be massive cyclones and floods that are made worse by sea level rise. For others it may be intense heat and permanent drought. In some places, it will be famine. But at least a quarter of the world’s population is going to have to move in the next 50 years.

Where to? No idea. With almost 8 billion people, the world is pretty full up already.

Interviewing a couple of climate scientists recently, I saw for the first time a graph, modeling the future of a runaway warming world, that explicitly included a "death" term. Mass death, that is.

Gwynne Dyer’s new book is "Growing Pains: The Future of Democracy (and Work)."

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