New studies on the Atlantic current system assess the threshold between natural fluctuations and a climate change-driven evolution
Is the Atlantic Meridional Overturning Circulation (AMOC) slowing down? Is this system of ocean currents, which is so important for our climate, likely to come to a halt in the future? Are the observed variations a natural phenomenon or are they already caused by human-induced climate change? Researchers from various scientific disciplines use a wide range of methods to better understand the gigantic oceanic circulation.
“The AMOC provides Europe with a mild climate and determines seasonal rainfall patterns in many countries around the Atlantic. If it weakens over the long term, this will also affect our weather and climate. Other consequences could be a faster rise in sea levels at some coasts or a reduction in the ocean’s ability to take up carbon dioxide and mitigate climate change”, Professor Dr. Mojib Latif, Head of the Research Unit: Marine Meteorology at GEOMAR Helmholtz Centre for Ocean Research Kiel, explains. “We depend on the AMOC in many ways – but so far, we can only guess how it will develop, and whether and how strongly we humans ourselves will push it towards a tipping point where an unstoppable collapse will take its course.”
Using 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 results have now been published in the scientific journal Nature Climate Change. According to the researchers, part of the North Atlantic is cooling – a striking contrast to the majority of ocean regions. All evaluations indicate that since the beginning of the 20th century, natural fluctuations have been the primary reason for this cooling. Nonetheless, the studies indicate that the AMOC has started to slow down in recent decades.
Climate models consistently predict a significant slowing of the current system in the future as carbon dioxide emissions continue to rise, the ocean continues to warm, and the melting of the Greenland ice sheet 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”, co-author and GEOMAR meteorologist Dr. Jing Sun points out.
Better observational data are needed to determine the critical limit, the authors conclude. “Systematic and sustained measurements of the changes already taking place across the Atlantic also allows us 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 Research Unit Physical Oceanography at GEOMAR is also co-author of the new publication. “At the moment, we do not see any clear signs 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 are on the relatively safe side of natural change.”
Latif, M., Sun, J., Visbeck, M., Bordbar M.H. (2022): Natural variability dominates Atlantic meridional overturning since 1900. Nature Climate Change, doi 10.1038/s41558-022-01342-4.
Utafiti mpya wa mfumo wa sasa wa Atlantiki unachunguza kizingiti kati ya mabadiliko ya asili na mabadiliko ya hali ya hewa - Je, Mzunguko wa Mzunguko wa Atlantiki wa Kusini (AMOC) unazidi? Je, mfumo huu wa mikondo ya bahari, ambao ni muhimu sana kwa hali ya hewa yetu, unaweza kukoma wakati ujao? Je, mabadiliko hayo ni ya asili au yametokana na mabadiliko ya hali ya hewa yanayosababishwa na wanadamu? Watafiti kutoka nyanja mbalimbali za kisayansi hutumia mbinu mbalimbali ili kuelewa vizuri mzunguko mkubwa wa bahari. <unk> AMOC hutoa Ulaya na hali ya hewa laini na huamua mifumo ya mvua ya msimu katika nchi nyingi karibu na Atlantiki. Ikiwa ita dhaifu kwa muda mrefu, hii pia itaathiri hali yetu ya hewa na hali ya hewa. "Mafaa ya bahari yaweza kuongezeka kwa kasi katika baadhi ya pwani au kupunguza uwezo wa bahari kuchukua kaboni dioksidi na kupunguza mabadiliko ya hali ya hewa,"" anasema Profesa Dr. Mojib Latif, Mkuu wa Kitengo cha Utafiti: Meteorolojia ya Bahari katika Kituo cha Utafiti wa Bahari cha GEOMAR Helmholtz." """Tunategemea AMOC kwa njia nyingi, lakini hadi sasa tunaweza tu kukisia jinsi itakavyositawi, na ikiwa na jinsi sisi wanadamu wenyewe tutasukuma kuelekea hatua ya kuanguka ambapo kuanguka kusikoweza kusimama kutachukua kozi yake, kwa hivyo kutumia data ya uchunguzi, uchambuzi wa takwimu na hesabu za mfano, timu iliyoongozwa na Profesa Latif imechunguza mabadiliko katika mfumo wa sasa kwa miaka mia moja iliyopita kwa undani zaidi." Matokeo ya utafiti huo yamechapishwa katika jarida la sayansi la Nature Climate Change. Kulingana na watafiti, sehemu ya Atlantiki Kaskazini inazidi baridi - tofauti kubwa na maeneo mengi ya bahari. Uchunguzi unaonyesha kuwa tangu mwanzo wa karne ya 20, mabadiliko ya asili yamekuwa sababu kuu ya baridi hii. Hata hivyo, utafiti unaonyesha kwamba AMOC imeanza kupunguza kasi katika miongo ya hivi karibuni. "Mifano ya hali ya hewa kwa mfululizo inatabiri ""kupungua kwa kasi kwa mfumo wa sasa"" katika siku zijazo kama uzalishaji wa kaboni dioksidi unaendelea kuongezeka, bahari inaendelea joto, na kuyeyuka kwa barafu ya Greenland inaongeza kasi." <unk> Matokeo yetu yanathibitisha matokeo ya awali ya kisayansi. Lakini swali linabaki ni ni kwa muda gani tutabaki katika ulimwengu wa mabadiliko ya asili na ni lini mabadiliko ya hali ya hewa yatachukua udhibiti wa AMOC. Kisha mwenendo itakuwa tu katika mwelekeo wa kudhoofika na hatari inaweza kuongezeka kwa kiasi kikubwa, mwandishi mwenza na GEOMAR meteorologist Dk Jing Sun anaonyesha. Waandishi hao wanakubali kwamba kuna uhitaji wa data bora zaidi za uchunguzi ili kuamua mpaka muhimu. "Uchunguzi wa utaratibu na endelevu wa mabadiliko ambayo tayari yanatokea katika Atlantiki pia inaruhusu kusema kwa uhakika zaidi ni nini mabadiliko ya hali ya hewa yanaathiri mfumo wa AMOC wa sasa na katika siku zijazo. """ Mkuu wa Kituo cha Utafiti wa Bahari ya Fizikia katika GEOMAR pia ni mwandishi mwenza wa chapisho jipya. <unk>Kwa sasa, hatuoni ishara yoyote ya wazi kwamba mfumo ni kupunguza kasi kwa kiasi kikubwa <unk> badala yake, ni fluctuating. Lakini kwa kuwa mifano ya hivi karibuni ya hali ya hewa inakubali kwamba kupungua kwa kiasi kikubwa kutatokea, tunapaswa kujua ni muda gani zaidi tuko upande salama wa mabadiliko ya asili. <unk> Latif, M., Sun, J., Visbeck, M., Bordbar M.H. "Mwaka wa 1920 na kuendelea, ""mabadiliko ya asili"" yamekuwa yakitawala mabadiliko ya meridian ya Atlantiki tangu mwaka wa 1900." Mabadiliko ya hali ya hewa (Nature, 101038-S41552-01342)