The links between cause and effect: French Environment Minister Nicolas Hulot's message to Donald Trump. Credit:AP Asked if the storms might force Mr Trump to rethink his climate change policy, Mr Hulot said: "What will change in the United States are the federal states, the cities, a whole section of society. I think that is what will make up for the reservations of the American President on the links between cause and effect." Irma, a deadly, devastating force of nature, rapidly coalesced from a low-pressure blip west of Africa into one of the most powerful Atlantic storms on record, following an unhindered atmospheric path and fed by unusually warm seas. A combination of many factors, experts said on Friday, set the stage for Irma's formation and helped the storm achieve its full thermodynamic potential, creating the monster tropical cyclone that wreaked havoc on the eastern Caribbean and may inflict widespread damage on Florida. "It got lucky," said John Knaff, a meteorologist and physical scientist for the National Oceanic and Atmospheric Administration (NOAA).

US President Donald Trump turns to leave after announcing the US would withdraw from the Paris climate accord. Credit:Bloomberg "This storm is in the Goldilocks environment for a major hurricane. It's bad luck for whoever is in its path, but that's what going on here." Brian Kahn, an atmospheric scientist and cloud specialist for NASA's Jet Propulsion Laboratory, called the ocean conditions that spawned Irma "absolutely ideal". Two man board up a property ahead of Hurricane Irma in Boca Raton, Florida on Friday. Credit:Bloomberg Balmy water temperatures along its trajectory ran deep beneath the surface and slightly higher than normal, by as much as a degree Fahrenheit in places, providing ample fuel for the storm's development, scientists said.

Irma also encountered little if any interference in the form of wind shear - sudden changes in vertical wind velocity that can blunt a storm's intensity - as it advanced at about 16 to 28 kilometres per hour, an ideal pace for hurricanes. The aftermath of Hurricane Irma in Virgin Gorda's Leverick Bay in the British Virgin Islands on Thursday. Credit:AP Its fortuitous path of least resistance was essentially ordained by a well-placed atmospheric ridge of high pressure that steered the storm by happenstance through some of the Caribbean's warmest waters as well as an area mostly devoid of wind shear. The result was a gargantuan storm that rapidly grew to a Category 5, the top of the Saffir-Simpson scale of hurricane strength, with sustained winds of 297 km/h , the most forceful ever documented in the open Atlantic. Three Hurricanes in a row, from left, in the Atlantic: Katia, Irma and Jose. Credit:NASA/NOAA

It also ranks as one of just five Atlantic hurricanes known to have achieved such wind speeds during the past 82 years. It lashed Cuba and the Bahamas as it drove toward Florida on Friday after hitting the eastern Caribbean with its tree-snapping winds, torrential rains and pounding surf, killing at least 21 people and leaving catastrophic destruction in its wake. Petrol bowsers close in West Palm Beach, Florida ahead of Hurricane Irma. Credit:Bloomberg By Friday night, Irma's winds had diminished to 250 kph and it was downgraded to a Category 4 storm, though still considered extremely dangerous. The tiny islands directly crossed by Irma, like Barbuda and St Martin, did little to weaken it, but the storm's intensity could be measurably diminished by a close encounter with a larger land mass, such as Cuba, en route to the US mainland, scientists said.

The damage after Irma passed through Dutch Saint Maarten, on Thursday. Credit:AP So powerful is Irma that it may end up dampening another Category 4 storm in its wake, Hurricane Jose, which like Irma originated off the west coast of Africa and was following a similar course. Waters already plied by Irma could be left a bit cooler, robbing Jose of potential energy, and "outflows" from Irma could produce wind shear for Jose, said Scott Braun, a research meteorologist for NASA's Goddard Space Flight Centre. Another hurricane is also in the wings: Katia, which is expected to soon have winds topping 177 km/h , could bring serious misery to Mexico, already suffering by the strongest earthquake to hit it in 100 years. It made landfall on Friday near the working-class beach resort of Tecolutla in the state of Veracruz on the Mexican Gulf coast, the US National Hurricane Center (NHC) said. The storm landed with sustained winds 75 mph (120 km/h) and was expected to weaken rapidly over the next day.

Knaff said it was no surprise that the advent of Irma coincided with the precise peak of the Atlantic hurricane season. Much less certain is the role of global climate from human-induced atmospheric increases in heat-trapping "greenhouse" gases, scientists said. There is consensus that climate change has raised sea levels, which is likely to exacerbate hurricane storm surges. Rising ocean temperatures have been clearly documented as well. Research is divided on whether global warming will make tropical cyclones more frequent, though data from climate modelling suggests a higher probability for stronger, wetter hurricanes in the Atlantic when they do occur, said Tom Knutson, a climate research scientist for NOAA.

Loading "We think, based on model simulations that climate change is having an effect, making storms slightly more intense with higher rainfall rates, but these changes are not huge and we cannot yet clearly detect them in observations," he said. Reuters