Cli­mate

Brace for more El Nino events

Farms & Farm Machinery - - Contents - writes Har­ri­son Hunkin

The fre­quency of ex­treme El Niño weather events is set to in­crease re­gard­less of whether the global tem­per­a­ture sta­bilises, the CSIRO says.

Re­search pub­lished in Na­ture Cli­mate Change by a team headed by CSIRO re­searcher Dr Guo­jian Wang pre­dicts El Nino events will dou­ble by the year 2050, and con­tinue on this path for a fur­ther cen­tury after the global mean tem­per­a­ture is sta­bilised to the Paris agree­ment tar­get of 1.5°C above prein­dus­trial lev­els.

“Cur­rently the risk of ex­treme El Niño events is around five events per 100 years,” Wang says.

“This dou­bles to ap­prox­i­mately 10 events per 100 years by 2050, when our mod­elled emis­sions sce­nario (RCP 2.6) reaches a peak of 1.5C warm­ing.”

The mod­els were run us­ing the In­ter­gov­ern­men­tal Panel on Cli­mate Change’s low­est emis­sions sce­nario (RCP2.6) which re­quires neg­a­tive emis­sions late in the cen­tury.

“After this, as faster warm­ing in the east­ern equa­to­rial Pa­cific per­sists, the risk of ex­treme El Niño con­tin­ues up­wards to about 14 events per 100 years by 2150,” Wang says.

“This re­sult is un­ex­pected and shows that fu­ture gen­er­a­tions will ex­pe­ri­ence greater cli­mate risks as­so­ci­ated with ex­treme El Niño events than seen at 1.5C warm­ing.”

BOM BLAST

The BoM (Bureau of Me­te­o­rol­ogy) says an El Niño oc­curs when sea sur­face tem­per­a­tures in the cen­tral and east­ern trop­i­cal Pa­cific Ocean be­come sub­stan­tially warmer than av­er­age, and this causes a shift in at­mo­spheric cir­cu­la­tion.

“Typ­i­cally, the equa­to­rial trade winds blow from east to west across the Pa­cific Ocean,” said BoM. “El Niño events are as­so­ci­ated with a weak­en­ing, or even re­ver­sal, of the pre­vail­ing trade winds.

“Warm­ing of ocean tem­per­a­tures in the cen­tral and east­ern Pa­cific causes this area to be­come more favourable for trop­i­cal rain­fall and cloud devel­op­ment. As a re­sult, the heavy rain­fall that usu­ally oc­curs to the north of Aus­tralia moves to the cen­tral and east­ern parts of the Pa­cific basin.”

DROUGHT MAKER

Aus­tralia’s agri­cul­tural sec­tor suf­fers se­verely dur­ing El Niño episodes as they of­ten lead to drier con­di­tions that tran­si­tion into drought, the body says. El Niño episodes last for a year with the great­est af­fects hap­pen­ing dur­ing winter and spring.

The El Niño event of 2002-03 is a good ex­am­ple of how the weather pat­tern can im­pact Aus­tralian agri­cul­ture.

That El Niño brought a drought which ranks along­side the ex­treme droughts of 1902 and 1982-83 as one of the coun­try’s worst in terms of sever­ity.

A series of dry years in the south­ern ar­eas in­ten­si­fied the ef­fects on the en­tire coun­try, the BoM says.

The ex­treme dry­ness seen dur­ing the 2002-03 El Niño mixed with record-break­ing heat led to the se­vere bush­fires in east­ern NSW, Can­berra and the moun­tains of south­east NSW and east­ern Vic­to­ria. Wide­spread wa­ter short­ages were also seen, high­light­ing the im­pact El Niño pat­terns can have Down Un­der.

RE­CENT EX­TREMES

Cen­tre for South­ern Hemi­sphere Oceans re­search direc­tor and report co-au­thor Dr Wenju Cai, says the three most ex­treme El Niño pat­terns have oc­curred in the last 35 years.

“The most se­vere pre­vi­ous ex­treme El Niño events oc­curred in 1982/83, 1997/98 and 2015/16, years as­so­ci­ated with world­wide cli­mate ex­tremes,” said Cai.

“Ex­treme El Niño events oc­cur when the usual El Niño Pa­cific rain­fall cen­tre is pushed east­ward to­ward South Amer­ica, some­times up to 16,000km, caus­ing mas­sive changes in the cli­mate. The fur­ther east the cen­tre moves, the more ex­treme the El Niño.

“This pulls rain­fall away from Aus­tralia bring­ing con­di­tions that have com­monly re­sulted in in­tense droughts across the na­tion,” Cai adds. “Dur­ing such events, other coun­tries like In­dia, Ecuador, and China have ex­pe­ri­enced ex­treme events with se­ri­ous so­cio-eco­nomic con­se­quences.”

It’s not all doom and gloom, though. While pre­vi­ous re­search sug­gests that ex­treme La Niña (op­po­site of El Niño) events would dou­ble un­der a 4.5C warm­ing sce­nario, find­ings in­di­cate that un­der a sce­nario of cli­mate sta­bil­i­sa­tion of 1.5C warm­ing, there would be lit­tle to no change to La Niña events, Cai says.

The re­search was con­ducted by re­searchers at the Ho­bart­based Cen­tre for South­ern Hemi­sphere Oceans Re­search, an in­ter­na­tional col­lab­o­ra­tion be­tween the CSIRO, Qing­dao Na­tional Lab­o­ra­tory for Marine Sci­ence and Tech­nol­ogy, the Univer­sity of New South Wales, and the Univer­sity of Tas­ma­nia.

The Bureau of Me­te­o­rol­ogy rou­tinely mon­i­tors for EL Niño episodes. Fore­casts take into ac­count the sur­face and sub­sur­face tem­per­a­ture pat­terns across the trop­i­cal Pa­cific Ocean, vari­a­tions in trade wind strength and at­mo­spheric pres­sure, and ocean cur­rents.

The BoM also analy­ses the at­mo­spheric and oceanic con­di­tions through cli­mate mod­els de­signed for long-range sea­sonal out­looks. The oc­cur­rence of an El Niño re­quires ocean and at­mo­spheric anom­alies to come to­gether and be­come sel­f­re­in­forc­ing, it says.

For the most re­cent in­for­ma­tion on El Niño or La Niña events, visit the Bureau’s ENSO Wrap-Up and ENSO tracker web pages, both up­dated every fort­night.

Photo: kris­tian­bell/RooM/Getty Im­ages

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