Do we need a smoking gun?

Climage change and hurricanes

PARIS, Sept 12, (AFP): Many climate scientists are convinced that megastorms Harvey and Irma – which left scores dead and caused massive economic losses – were boosted by global warming, but hesitate to say so in as many words. Call it the hurricane paradox. On the one hand, top experts point to the laws of physics, computer modelling, and measurable increases in sea levels and the temperatures of both ocean water and the atmosphere – all pointing to destructive tropical cyclones.

Taken together, they are like the overwhelming body of circumstantial evidence a prosecutor might lay out in a murder trial.

On the other hand, there is something crucial missing: the fingerprints on the weapon, the smokinggun proof that would convince a jury to lock up the culprit and throw away the key.

In climate science, that gold-standard evidence comes from observation over a long period of time.

“It is incredibly frustrating,” said Dann Mitchell, an expert on atmospheric circulation at the University of Bristol in England. “We still can’t say with 100 percent certainty that Hurricane Irma was enhanced by climate change, while with other extreme events – such as heat waves – we can.”

A lot of scientists, however, think the case is already solid enough to nail down a conviction.

“The physics are very clear: hurricanes get their destructive energy from ocean heat,” said Anders Levermann, a professor at the University of Potsdam in Germany.

“Greenhouse gas emissions from burning coal, oil and gas raise our planet’s temperatures and provide the energy for ever stronger tropical storms.”

And then there is the global ocean watermark, which has gone up 20 centimetres (eight inches) on average since the 1880s, and is set to rise far more by century’s end.

“We are extremely confident that sea level rise is happening and will continue to happen as the climate warms,” said Chris Holloway, a hurricane expert at the University of Reading. “This adds to the risk of storm surge flooding from any event,” he told AFP.

But – convincing as they may be – these remain “it stands to reason” arguments, not direct measurements of the major tropical storms known variously around the world as hurricanes, cyclones and typhoons.

And that’s where things get a little dicey, and scientific opinion divides.

“Increased intensity of storms is an expected climate change signature, but it is too early to tell if this particular storm was enhanced in this way,” Mitchell said of Irma.

The problem, he and other scientists caution, is several-fold.

To begin with, major tropical storms – category 4 or 5 on the Saffir-Simpson scale, keyed to wind speed – are very rare compared to heat waves, drought or intense bouts of rainfall.

In science, a small sample size makes it hard to pick out patterns, a problem exacerbated in this case by poor quality data only reaching back a few decades.

Also: WASHINGTON:

Climate change is threatening the Latin American zones most favorable for growing coffee, according to a study out Monday that warns seed production could drop by nearly 90 percent by 2050.

The study suggests high quality coffees are most at risk – with Arabica coffee unable to withstand even slight fluctuations in temperature, humidity and sunlight.

Robusta coffee, mostly grown in Africa to be made into instant coffee, is slightly more resistant.

ON BOARD THE PAPAL PLANE:

Pope Francis on Monday slammed climate change doubters as “stupid” in the wake of a spate of hurricanes that have thrashed the US, Mexico and the Caribbean.

“Those who deny it (climate change) should go to the scientists and ask them. They are very clear, very precise,” the pontiff said Monday during a press conference on the return leg of a five-day Colombia trip.

“A phrase from the Old Testament comes to mind: ‘man is stupid, a stubborn, blind man’,” he added.