Does cli­mate vary more from cen­tury to cen­tury when it is warmer?

Tehran Times - - SCIENCE -

Cen­tury-scale cli­mate vari­abil­ity was en­hanced when the Earth was warmer dur­ing the Last In­ter­glacial pe­riod (129-116 thou­sand years ago) com­pared to the cur­rent in­ter­glacial (the last 11,700 years), ac­cord­ing to a new UCL-led study.

The find­ings re­vealed that the Last In­ter­glacial pe­riod was punc­tu­ated by a se­ries of cen­tury-scale arid events in south­ern Europe and cold wa­ter-mass ex­pan­sions in the North At­lantic.

Assess­ing nat­u­ral cli­mate vari­abil­ity un­der rel­a­tively warm con­di­tions is cru­cial to in­form pro­jec­tions un­der fu­ture car­bon emis­sion sce­nar­ios. Pro­fes­sor Chro­nis Tzedakis (UCL Geog­ra­phy), study lead au­thor, said: “The Last In­ter­glacial is par­tic­u­larly rel­e­vant be­cause it pro­vides in­sights into cli­mate pro­cesses dur­ing a pe­riod of ex­cess warmth.”

In­ter­glacial pe­riod

The Last In­ter­glacial pe­riod con­tained an in­ter­val of in­tense Arc­tic warm­ing, with sur­face air tem­per­a­tures es­ti­mated at 3-11°C above pre-in­dus­trial, com­pa­ra­ble to high-lat­i­tude warm­ing sce­nar­ios for the end of this cen­tury.

Global sea-level dur­ing the Last In­ter­glacial is es­ti­mated to have been ~6-9 m above present, with 0.6-3.5 m de­rived from melt­ing of the Green­land Ice Sheet.

Pre­vi­ously, sev­eral North At­lantic and Eu­ro­pean records have de­tected cen­tury-scale changes in tem­per­a­ture and pre­cip­i­ta­tion within the Last In­ter­glacial, but there has been con­sid­er­able un­cer­tainty over the tim­ing, ex­tent and ori­gin of these cli­mate os­cil­la­tions.

This new study by in­ter­na­tional re­searchers from twelve in­sti­tu­tions used ma­rine and ter­res­trial ge­o­log­i­cal ar­chives, cou­pled with cli­mate model ex­per­i­ments, to cre­ate the most de­tailed time­line of ocean and at­mo­sphere changes in the North At­lantic and south­ern Europe dur­ing the Last In­ter­glacial.

To ad­dress the un­cer­tain­ties in com­par­ing records from dif­fer­ent en­vi­ron­ments, re­searchers pro­duced a “strati­graphic ‘rosetta stone’ by an­a­lyz­ing dif­fer­ent fos­sils from the same sed­i­ment sam­ples in a ma­rine core off Lis­bon,” said Dr. Luke Skin­ner (Cam­bridge Univer­sity) who led the palaeo­ceano­graphic analy­ses.

The “ma­rine core also con­tained pollen trans­ported from the Ta­gus River into the deep sea, thus en­abling a di­rect com­par­i­son of veg­e­ta­tion and North At­lantic Ocean changes,” said Dr. Vasi­liki Mar­gari (UCL Geog­ra­phy), who un­der­took the pollen anal­y­sis.

Changes in veg­e­ta­tion, pri­mar­ily caused by vari­a­tions in the amount of rain­fall, were then linked to changes in the chem­i­cal sig­na­ture of rain­fall recorded in sta­lag­mites from Corchia Cave in north­ern Italy.

De­tailed ra­dio­met­ric dat­ing

The “Corchia record is par­tic­u­larly im­por­tant be­cause it is sup­ported by very de­tailed ra­dio­met­ric dat­ing us­ing the de­cay of ura­nium iso­topes, pro­duc­ing one of the best chronolo­gies for this pe­riod avail­able,” said Dr. Rus­sell Drys­dale (Univer­sity of Mel­bourne), who led the team study­ing the Ital­ian cave.

Cli­mate model ex­per­i­ments, un­der­taken by Dr. Lau­rie Men­viel and Dr. An­drea Taschetto of the Univer­sity of New South Wales Sydney, re­vealed that the spa­tial finger­print of these changes was con­sis­tent with dis­rup­tions of the At­lantic merid­ional over­turn­ing cir­cu­la­tion.

Green­land ice-melt and runoff as a re­sult of strong high-lat­i­tude warm­ing dur­ing the Last In­ter­glacial may have con­trib­uted to the weak­en­ing of the At­lantic merid­ional over­turn­ing cir­cu­la­tion and to the ob­served cli­mate changes.

Changes in veg­e­ta­tion, pri­mar­ily caused by vari­a­tions in the amount of rain­fall, were then linked to changes in the chem­i­cal sig­na­ture of rain­fall recorded in sta­lag­mites from Corchia Cave in north­ern Italy.

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