Nagraj Adve in The Wire:
Experts have voiced their surprise that Hurricane Irma has surfaced so soon after Hurricane Harvey. In fact, Irma is being accompanied by Hurricanes Jose to its east and Katia to its west. Jose, itself close to Category 5, will be the second to hit the Caribbean islands in just a couple of days. It’s made some raise what is increasingly becoming an obvious question: to what extent does global warming have a role to play? To which I would add one voiced less frequently: why should those least responsible for global warming have to constantly face its effects? And what does it bode for the future?
Ocean water temperatures need to cross 26.5º C to depths of 50 metres for tropical cyclones to form. (It’s a necessary condition but not a sufficient one. Other favourable conditions are needed, for instance the absence of winds at a higher level that can interfere with hurricane formation.) Over 60% of the extraordinary amount of heat energy trapped by greenhouse gases since 1971 – about 170,000 billion billion joules – has gone into the upper oceans, according to the IPCC’s Fifth Assessment Report. It’s a number so bewilderingly large that an easier way of conceptualising it is this: averaged out each year, it equals 40-times the entire annual energy consumption of the US. The consequently warmer upper ocean waters ensure that, when other conditions are right, there’s a greater chance of hurricanes forming and sustaining themselves for a longer duration. Or getting more intense. Or them forming one after the other, as has happened with Irma and Jose.
Another way global warming is implicated has to do with storm surges now pummelling Cuba, followed by the US over the weekend. Swirling hurricane winds pull in massive volumes of sea water. Out in the open sea, those waters are forced downwards into the ocean depths. But once the hurricane approaches land, the shallower seabed means the excess water pulled in by the hurricane has nowhere to go, so it just piles up and overwhelms the shore.