Investigations of the Atlantic flow system

In a pub­li­ca­tion in the jour­nal Nature Cli­mate Change, researchers from Kiel once again con­tribute to the under­stand­ing of changes in the Atlantic Merid­ion­al Over­turn­ing Cir­cu­la­tion — known to the pub­lic as the “Gulf Stream Sys­tem”. It is just as impor­tant for the glob­al cli­mate as it is for cli­mate events in Europe. The research focus­es on whether human-induced cli­mate change is already slow­ing the ocean­ic over­turn­ing cir­cu­la­tion. Accord­ing to the new study, nat­ur­al vari­a­tions still dom­i­nate. Improved obser­va­tion sys­tems could help detect human influ­ence on the cur­rent sys­tem at an ear­ly stage.

Is the Atlantic Merid­ion­al Over­turn­ing Cir­cu­la­tion (AMOC) slow­ing down? Will this sys­tem of ocean cur­rents, which is so impor­tant for our cli­mate, pos­si­bly come to a stand­still in the future? Are the observed fluc­tu­a­tions of nat­ur­al ori­gin or already a con­se­quence of man-made cli­mate change? Researchers from var­i­ous sci­en­tif­ic dis­ci­plines are using a wide range of meth­ods to try to bet­ter under­stand the gigan­tic ocean­ic over­turn­ing movement.

“The AMOC pro­vides mild cli­mate in Europe and deter­mines sea­son­al rain­fall pat­terns in many coun­tries around the Atlantic. If it weak­ens over the long term, it will also affect our weath­er and cli­mate. It could also cause sea lev­els to rise faster on some coasts and reduce the ocean’s abil­i­ty to absorb car­bon diox­ide and mit­i­gate cli­mate change. We depend on the AMOC in many ways — and yet so far we can only guess how it will evolve, and whether and how much we humans our­selves will dri­ve it toward a tip­ping point where an unstop­pable col­lapse runs its course.”

- Pro­fes­sor Dr. Mojib Latif, Head of the Research Unit Mar­itime Meteorology

Using eval­u­a­tions of obser­va­tion­al data, sta­tis­ti­cal analy­ses and mod­el cal­cu­la­tions, a team led by Pro­fes­sor Latif has there­fore exam­ined changes in the cur­rent sys­tem over the past one hun­dred years in greater detail. The researchers have now pub­lished their results in the jour­nal Nature Cli­mate Change. Accord­ing to the results, part of the North Atlantic is cool­ing — a strik­ing con­trast to the vast major­i­ty of ocean regions. The analy­ses indi­cate that nat­ur­al fluc­tu­a­tions have been pri­mar­i­ly respon­si­ble for this cool­ing since the begin­ning of the 20th cen­tu­ry. Nonethe­less, the stud­ies point to an incip­i­ent slow­ing of the AMOC in recent decades.

Cli­mate mod­els con­sis­tent­ly pre­dict a sig­nif­i­cant slow­ing of the cur­rent sys­tem in the future as our car­bon diox­ide emis­sions con­tin­ue to rise, the ocean con­tin­ues to warm, and the melt­ing of Green­land ice accel­er­ates. “Our results con­firm ear­li­er sci­en­tif­ic find­ings. But the ques­tion remains how long we will remain in the realm of nat­ur­al vari­abil­i­ty and when cli­mate change will take con­trol of the AMOC. Then the trend would only be in the direc­tion of weak­en­ing and risks could increase sig­nif­i­cant­ly,” empha­sizes Dr. Jing Sun, mete­o­rol­o­gist at GEOMAR and co-author of the study.

Bet­ter obser­va­tion­al data are need­ed to deter­mine the crit­i­cal lim­it, the authors con­clude. “If we sys­tem­at­i­cal­ly and per­ma­nent­ly mea­sure the changes already tak­ing place in all regions of the Atlantic, we will also be able to say with greater cer­tain­ty what influ­ence cli­mate change has on the AMOC cur­rent sys­tem today and in the future,” says Pro­fes­sor Dr. Mar­tin Vis­beck. The head of the Phys­i­cal Oceanog­ra­phy research unit at GEOMAR is also co-author of the pub­li­ca­tion. “We don’t see any sure signs at the moment that the sys­tem is slow­ing down dra­mat­i­cal­ly — rather, it is fluc­tu­at­ing. But since the lat­est cli­mate mod­els agree that a sig­nif­i­cant reduc­tion will occur, we should know how much longer we’re on the rel­a­tive­ly safe side of nat­ur­al change.”