The Weekend Australian

Fresh in­sight into cli­matic ef­fects of cos­mic changes

Re­searchers sug­gest tem­per­a­tures on Earth don’t fluc­tu­ate only be­cause of green­house gases

- GRA­HAM LLOYD EN­VI­RON­MENT ED­I­TOR Space · Science · Ecology · Earth · Solar System · Milky Way Galaxy · China · United Kingdom · Japan · Kobe · Kobe University · Intergovernmental Panel on Climate Change · Nature Communications · Mongolia · Northumbria · Independent Police Complaints Commission · Monash University

Sand de­posits near the Gobi Desert in China may seem a strange place to look for ev­i­dence that cos­mic rays can con­trol how clouds are formed and the im­pact they have on Earth’s cli­mate.

But Ja­panese sci­en­tists have mea­sured the size of sand grains and the dis­tance they trav­elled 780,000 years ago to add a new level of un­der­stand­ing to one of the ques­tions that con­tin­ues to baf­fle cli­mate sci­ence: clouds.

The find­ings, pub­lished in Nature, point to big trends in nat­u­ral vari­a­tion of past and fu­ture cli­mate that op­er­ate apart from green­house gas lev­els.

The study adds weight to a con­tentious the­ory by Dan­ish re­searcher Hen­rik Svens­mark, of the Dan­ish Na­tional Space In­sti­tute in Copen­hagen, which uses cos­mic rays and clouds to ques­tion the sen­si­tiv­ity of cli­mate to car­bon diox­ide in the at­mos­phere.

And it follows a study of 120,000 years of so­lar cy­cles by Valentina Zharkova, of Bri­tain’s Northum­bria Univer­sity, which says a nat­u­ral sun cycle will add 2.5C warm­ing to Earth’s cli­mate in com­ing cen­turies on top of any im­pact from ris­ing green­house gases.

Nei­ther the re­searchers nor the Ja­panese re­search team dis­pute that car­bon diox­ide is a green­house gas with im­pli­ca­tions for the cli­mate. But if they are to be be­lieved, our un­der­stand­ing of the sun’s role in cli­mate cy­cles is start­ing to burn brighter.

Zharkova’s re­search, pub­lished in Sci­en­tific Re­ports, con­cen­trates on a cycle that varies the dis­tance be­tween the Earth and the sun. She was pre­vi­ously best known for re­search on sunspot cy­cles that in­di­cate a cooling in­flu­ence on the Earth’s cli­mate across the next two decades. Through sta­tis­ti­cal anal­y­sis of data gath­ered dur­ing the sunspot re­search, Zharkova and her col­leagues iden­ti­fied that this cycle of move­ment, known as a su­per-grand cycle, takes about 2000 years to com­plete.

She and her team have been able to re-cre­ate al­most 60 su­per­grand cy­cles, go­ing back 120,000 years. Their re­search has es­tab­lished that the cur­rent su­per­grand cycle be­gan be­tween 1645 and 1715, dur­ing the Maun­der Min­i­mum pe­riod in which the sun was ex­pe­ri­enc­ing far fewer sunspots and the Earth’s tem­per­a­ture de­creased as a re­sult.

The au­thors say we are now in the grow­ing — or warm­ing — phase of the cycle, which is ex­pected to reach its peak by the year 2600. By this time the Earth’s tem­per­a­ture is ex­pected to have in­creased by be­tween 2.5C and 3C.

They say this rise is ex­pected to happen in ad­di­tion to any rise re­lated to man-made ac­tiv­ity such as car­bon emis­sions.

The cycle then will en­ter the cooling phase, dur­ing which the sun will move slightly far­ther away from the Earth. This is ex­pected to last un­til the year 3700.

Mean­while, re­searchers at Ja­pan’s Kobe Univer­sity pro­vide an op­por­tu­nity to re­think the role of clouds in cli­mate.

Lead au­thor Masayuki Hy­odo has found a new way to test a the­ory that when ga­lac­tic cos­mic rays in­crease, so do low clouds, and when cos­mic rays de­crease, clouds fol­low suit.

“The In­ter­gov­ern­men­tal Panel on Cli­mate Change has dis­cussed the im­pact of cloud cover on cli­mate in their eval­u­a­tions, but this phe­nom­e­non has never been con­sid­ered in cli­mate pre­dic­tions due to in­suf­fi­cient phys­i­cal un­der­stand­ing of it,” Hy­odo says.

The re­search builds on the so­called Svens­mark Ef­fect, which is a hy­poth­e­sis that ga­lac­tic cos­mic rays in­duce low cloud for­ma­tion and in­flu­ence the Earth’s cli­mate.

In De­cem­ber 2017, Svens­mark pub­lished re­search in Nature Com­mu­ni­ca­tions he said in­di­cated the im­pact of changes in so­lar ac­tiv­ity on Earth’s cli­mate was up to seven times greater than cli­mate mod­els sug­gested.

The claimed break­through was in un­der­stand­ing how cos­mic rays from su­per­novas in­ter­act with the so­lar mag­netic field, with vari­a­tions in that mag­netic field re­flected in the in­ten­sity of cos­mic rays reach­ing the Earth.

These vari­a­tions in­flu­ence the den­sity of cloud cover, which in turn has an ef­fect on the Earth’s cli­mate.

This has im­pli­ca­tions for how sensitive cli­mate is to ris­ing lev­els of car­bon diox­ide.

It is an ac­tive field of study with dif­fer­ent re­searchers ar­riv­ing at dif­fer­ent con­clu­sions.

The IPCC re­ports have a wide range of pos­si­ble fig­ures for cli­mate sen­si­tiv­ity.

Hy­odo’s re­search ap­proaches the same ques­tion posed by Svens­mark but from a dif­fer­ent, and un­usual, per­spec­tive. He says tests based on re­cent me­te­o­ro­log­i­cal ob­ser­va­tion data show only minute changes in the amounts of cos­mic rays and cloud cover, mak­ing it dif­fi­cult to prove the the­ory.

In an ar­ti­cle based on the re­search, Hy­odo ex­plains how re­searchers went look­ing for clues dur­ing the last ge­o­mag­netic re­ver­sal tran­si­tion three-quar­ters of a mil­lion years ago. The the­ory was that dur­ing the ge­o­mag­netic re­ver­sal the amount of cos­mic rays in­creased dra­mat­i­cally and there was also a large in­crease in cloud cover. In China’s Loess Plateau, just south of the Gobi Desert near the bor­der with Mon­go­lia, dust has been trans­ported for 2.6 mil­lion years to form lay­ers of wind­blown silt up to 200m thick.

The re­searchers pro­pose that win­ter mon­soons would be­come stronger if there were in­creased cloud cover dur­ing the ge­o­mag­netic re­ver­sal. They found ev­i­dence that for a pe­riod of 5000 years dur­ing the re­ver­sal, coarser grains of silt had been de­posited over a much greater dis­tance.

The strong win­ter mon­soons had co­in­cided with the pe­riod dur­ing the re­ver­sal when the Earth’s mag­netic strength fell to less than one quar­ter and cos­mic rays in­creased by more than 50 per cent.

“This sug­gests that the in­crease in cos­mic rays was ac­com­pa­nied by an in­crease in low-cloud cover, the um­brella ef­fect of the clouds cooled the con­ti­nent, and Siberian high atmospheri­c pres­sure be­came stronger,” re­searchers say. There was also ev­i­dence of an an­nual av­er­age tem­per­a­ture drop of 2C to 3C.

Svens­mark tells Inquirer the lat­est re­search is in­de­pen­dent con­fir­ma­tion of the role of cos­mic rays on cli­mate. He says Hy­odo’s re­search deals with Earth’s mag­netic field and is one of three pos­si­ble ways cos­mic rays can af­fect our planet’s at­mos­phere.

One is a change in the num­ber of su­per­novas in the so­lar sys­tem’s neigh­bour­hood; an­other is that so­lar ac­tiv­ity can mod­u­late the num­ber of cos­mic rays reach­ing the Earth; and the third is changes in the Earth’s mag­netic field.

Svens­mark says he is happy to see a new study that seems to find a con­nec­tion.

Michael Asten, ad­junct se­nior re­search fel­low at Monash Univer­sity’s school of Earth at­mos­phere and en­vi­ron­ment, says sci­en­tists have barely scratched the sur­face of the task of recog­nis­ing and modelling nat­u­ral cy­cles of cli­mate change.

The as­so­ci­a­tion be­tween cos­mic ray ac­tiv­ity and global cli­mate is com­plex be­cause the cos­mic ray record tells us of en­ergy reach­ing the top of Earth’s at­mos­phere.

Global cli­mate vari­a­tions are the re­sult of vari­a­tions in cloud cover, atmospheri­c cir­cu­la­tion patterns and ocean cir­cu­la­tion patterns as well as the ac­tual lu­mi­nos­ity of the sun.

Asten says Svens­mark’s ex­pla­na­tion is not ac­cepted by the vast ma­jor­ity of re­searchers, but in time his the­ory may well be seen as a sem­i­nal part of new insights into an in­cred­i­bly com­plex set of sun-Earth-cli­mate in­ter­ac­tions.

 ?? MARK EVANS ?? The den­sity of cloud cover af­fects the planet’s cli­mate
MARK EVANS The den­sity of cloud cover af­fects the planet’s cli­mate
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