WARM­ING’S LINKS WITH DIS­AS­TERS? CHANCE IS ALSO A POW­ER­FUL FORCE

▶ It’s easy to blame re­cent dis­as­ters on cli­mate change but the stats just don’t add up. Robert Matthews re­ports

The National - News - - NEWS | SCIENCE -

Will it never end? Hur­ri­canes in the Caribbean, a huge earth­quake near Mex­ico, dev­as­tat­ing floods in South Asia. And those are just what our home planet has thrown at us.

In re­cent days the Sun has joined in, blast­ing the Earth with ra­di­a­tion in the so­lar equiv­a­lent of sev­eral Cat­e­gory 5 storms. It dis­rupted ra­dio com­mu­ni­ca­tion and pro­duced au­ro­ral dis­plays over North Amer­ica’s south­ern states.

Such a litany of may­hem in so short a time may be un­prece­dented. It has al­ready had a dev­as­tat­ing im­pact on the lives of mil­lions. Even those of us not di­rectly af­fected have been left with an eerie sense of ap­proach­ing apoc­a­lypse.

Sci­en­tists are di­vided about the sig­nif­i­cance of it all. Some in­sist that the spate of se­vere hur­ri­canes in the Caribbean can­not be put down to chance. They ar­gue that it must be the re­sult of cli­mate change, with global warm­ing spawn­ing more vi­o­lent hur­ri­canes.

Oth­ers are equally ve­he­ment that, while con­sis­tent with a warmer world, there are dan­gers in read­ing too much into re­cent events.

The most re­li­able ev­i­dence of a link comes from analysis of records dat­ing back a cen­tury or more – and this shows no sign of a trend to­wards in­creas­ingly vi­o­lent storms.

Demon­strat­ing cause and ef­fect is one of the most dif­fi­cult prob­lems in sci­ence, not least be­cause of the abil­ity of pure chance to pro­duce spu­ri­ous pat­terns.

Some years ago, a Har­vard grad­u­ate stu­dent set up a com­puter pro­gram that scoured the web for ran­dom col­lec­tions of data. Us­ing the same tech­niques rou­tinely used by re­searchers search­ing for cor­re­la­tions, the pro­gram found count­less sta­tis­ti­cally sig­nif­i­cant but mean­ing­less re­la­tion­ships.

In one ex­am­ple, it re­vealed that if the num­ber of swim­ming pool ac­ci­dents in the US an­nu­ally were plot­ted out over a decade, they were strongly cor­re­lated to the num­ber of films star­ring Ni­co­las Cage.

Of course, ex­tend the data set far enough and the cor­re­la­tion van­ishes. Swim­ming pool ac­ci­dents pre­date even Cage’s long ca­reer.

But the problem with many data sets, such as those link­ing global warm­ing to its sup­posed con­se­quences, is that it re­mains un­clear just how long it takes for the real sig­nal to emerge from the ran­dom noise.

This is why most cli­mate sci­en­tists re­main re­luc­tant to link the re­cent spate of hur­ri­canes to global warm­ing, de­spite hav­ing few doubts that global warm­ing is real and makes such events more prob­a­ble.

But what of the con­flu­ence of the other dis­as­ters, such as the worst floods in Bangladesh and neigh­bour­ing states for a decade, and the strong­est earth­quake to strike Mex­ico since 1787?

Again, the trick­ery of ran­dom­ness is the most likely ex­pla­na­tion. Chance events are sur­pris­ingly prone to ap­pear­ing in “runs”, even when com­pletely un­con­nected.

Toss a coin once a day for a month and prob­a­bil­ity the­ory shows that you’re likely to wit­ness runs of about half a dozen heads or tails – enough to raise sus­pi­cions that there’s some­thing odd go­ing on.

Add in the sheer plethora of nat­u­ral dis­as­ters that strike in any given year and the po­ten­tial for runs among them be­comes con­sid­er­able.

In short, see­ing sig­nif­i­cance in the global spate of dis­as­ters makes no sense. It’s hard enough to make a case for the re­cent rash of strong hur­ri­canes be­ing a “smok­ing gun” of cli­mate change.

It’s also be­side the point, be­cause what­ever their cause these dis­as­ters still hap­pened. But a ra­tio­nal analysis of their ef­fect re­veals grounds for op­ti­mism about the fu­ture.

Dev­as­tat­ing hur­ri­canes were a fea­ture of our planet long be­fore the emer­gence of hu­man be­ings. Even if the world’s gov­ern­ments agreed to stop burn­ing fos­sil fuel to­mor­row, hur­ri­canes would re­main a ma­jor threat in the trop­ics.

Yet in the past few decades, im­pres­sive progress has been made in mit­i­gat­ing im­pacts.

Hur­ri­canes can no longer strike with­out warn­ing, as one did in Galve­ston, Texas in 1900, killing about 10,000 – the dead­li­est in US his­tory. Their paths can be pre­dicted with rea­son­able ac­cu­racy days in ad­vance, al­low­ing com­mu­ni­ties at risk to be alerted.

Af­ter Hur­ri­cane An­drew in 1992, Florida’s con­struc­tion codes were up­graded, mak­ing build­ings far more re­sis­tant to dam­age and again sav­ing lives.

It is a sim­i­lar story with earth­quakes. In­creas­ing num­bers of coun­tries now in­sist on quake-re­sis­tant con­struc­tion, thus coun­ter­ing the ma­jor cause of deaths in earth­quake zones – homes that col­lapse.

Mex­ico City also has a quake-de­tec­tion sys­tem that gives about 60 sec­onds of warn­ing be­fore an im­pend­ing strike – enough time for those at risk to take cover. This helped to keep the toll from this month’s colos­sal quake to about 100. When the city was struck by a weaker event in 1985, it killed tens of thou­sands.

But there is one glar­ing ex­cep­tion to this trend – the im­pact of the re­cent floods in South Asia. The death toll in In­dia, Bangladesh and Nepal has ex­ceeded 1,000, and mil­lions have been left home­less.

The root cause is nei­ther the va­garies of na­ture nor the en­vi­ron­men­tal im­pact of hu­man ac­tiv­ity. It is much sim­pler than that, and much harder to solve – poverty.

When your ex­is­tence de­mands that you eke out a liv­ing in harm’s way, there is lit­tle that satel­lite im­agery or com­puter fore­cast­ing can do to pro­tect you.

Demon­strat­ing cause and ef­fect is one of the most dif­fi­cult prob­lems in sci­ence, not least be­cause of the abil­ity of pure chance to pro­duce spu­ri­ous pat­terns

Robert Matthews is vis­it­ing pro­fes­sor of sci­ence at As­ton Univer­sity, Birm­ing­ham, UK

AP

Hur­ri­cane Irma, cen­tre, ap­proaches Cuba, with Hur­ri­cane Ka­tia, left, in the Gulf of Mex­ico, and Hur­ri­cane Jose, right, in the At­lantic, but can this be blamed on global warm­ing?

Reuters

Hur­ri­cane Irma flat­tened many homes in Islamorada, in the Florida Keys, and much of the sun­shine state, but sci­en­tists are un­sure about what trig­gered Irma’s in­ten­sity

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