Is the Gulf Stream losing stability? If so, does it mean an ice age is coming?
In a recent issue of Nature Climate Change, mathematician and climatologist, Niklas Boers, used measurements of sea surface temperatures and salinity data across the Atlantic Ocean basin to produce a model that indicates that the Atlantic Meridional Overturning Circulation (AMOC) may soon suffer a major weakening. I’ll explain what such a weakening means for Earth’s global climate after we review several studies.
Atlantic Meridional Overturning Circulation
Most laypeople have never heard of the AMOC. However, most have heard of the Gulf Stream. The Gulf Stream refers to the flow of warm tropical water from the Gulf of Mexico and the Caribbean along the surface of the Atlantic Ocean toward western and northern Europe and Iceland; and the flow of cold Arctic Ocean water along the deep part of the Atlantic Ocean from the far northern Atlantic to the equatorial Atlantic. Without the Gulf Stream (see figure 1), western and northern Europe and Iceland would be much colder than they are. Those regions would be unable to sustain the large human populations that they presently do.
Figure 1: The Surface Part of the Gulf Stream
The Gulf Stream is part of the AMOC, which is the system of surface and deep currents throughout the Atlantic Ocean. It is mainly characterized by a northward flow of warm, salty water from the tropics along the upper layers of the Atlantic and the southward flow of cold, low-salinity water from the Arctic along the Atlantic’s deep layers (see figure 2).
Figure 2: Atlantic Meridional Overturning Circulation
Orange arrows show the warm, salty surface currents. Blue arrows show the cold, low-salinity deep currents. Credit: Summer K. Praetorius, Nature 556 (April 11, 2018): 180.
Observed AMOC Changes
In 2018, two papers published in Nature presented evidence of a slowdown in the AMOC. The first paper by Levke Caesar and his colleagues compared comprehensive sea surface temperature measurements in the Atlantic made over the past century with high-resolution climate models.1 This comparison showed that the AMOC had weakened by 15% since 1950.
The second paper by David Thornalley and his team of eleven researchers used data from sediment cores drilled on the seafloor off the US East Coast, Nova Scotia, Newfoundland, Labrador, and Baffin Island.2 Thornalley’s team measured the sizes of sediment grains in these cores to determine how rapidly deep ocean currents were flowing throughout the past 1,600 years. Their measurements revealed that the AMOC “has been weaker during the past 150 years than at any time during the past 1,600 years.”3 They agree with the first research team that the degree of weakening was 15%.
Both research teams concluded that the AMOC weakening has been initiated and sustained by human-caused global warming,leading to significant melting of the Greenland Ice Sheet. Cool, fresh meltwater from ice sheets and glaciers on Greenland, Baffin Island, Iceland, and the Arctic Ocean, they say, blunted the AMOC.
Niklas Boers at the Potsdam Institute of Climate Impact Research noted that direct observations of AMOC strength have been available only for the past two decades.4 He analyzed these direct observations of sea surface temperatures and salinity data across the entire Atlantic Ocean basin. His analysis showed that during the last century “the AMOC may have evolved from relatively stable conditions to a point close to a critical transition.”5 He adds that his analysis gives “a first indication that the Atlantic Ocean circulation system may be losing stability.”6
Climate Change and Ice Age Onset Implications
The last time the AMOC experienced a major disruption was during the Younger Dryas cooling event (see figure 3). I described this event in detail in my book Weathering Climate Change.7 This event was initiated 12,800 years ago by a huge asteroid striking the Hiawatha Icefield in northwestern Greenland. The collision melted huge quantities of ice on Greenland and changed the drainage of Lake Agassiz, an enormous glacial lake (see figure 4), from its flow into the Gulf of Mexico to a flow into the Beaufort Sea and the Gulf of St. Lawrence.
Figure 3: Younger Dryas Cooling Event Diagram credit: Hugh Ross
Figure 4: Lake Agassiz Immediately before the Younger Dryas Background image credit: NASA
The combination of melted Greenland ice and glacial meltwater flowing into the North Atlantic Ocean brought the AMOC to a virtual halt. This halting of the AMOC caused Europe and North America to become much colder and resulted in a global cooling of more than 10°C (18°F) that lasted for 1,200 years. As I explained in my book, the Younger Dryas cooling event occurred at a time when both Earth’s axial tilt variation and Earth’s orbital eccentricity variation were warming our planet. The Younger Dryas cooling event prevented Earth’s surface temperature from rising to 2–3°C above its present value, which would have melted the polar ice cap, caused huge amounts of snow to fall on Canada and Siberia, and brought on the next ice age.
In chapter 18 of my book I explained why global warming, if left unchecked, always brings on global cooling. The papers published in 2018 and Boers’s recent work show that the risk of a relatively imminent ice age onset could be greater than previously thought. Further weakening of the AMOC would first make western Europe much warmer than it is8 and then make Canada, Europe, and the northern parts of the United States much colder than they are now. Such weakening will also disrupt the tropical monsoon system and the climates of the Amazon rainforest, the Antarctic, and the Southern Ocean.9 As I described in a previous article, What Will Happen if Arctic Sea Ice Loss Continues?, for the seven seas that comprise the Arctic Ocean, since 1750 the summer sea ice mass loss has ranged from 31% to 99%. Meanwhile, the winter sea ice mass loss has ranged from 1% to 45%. In particular, additional loss of winter sea ice mass will cause more snow to fall on Canada, Siberia, and northern Europe and lead to the buildup of ice sheets over those regions.
Unlike during the Younger Dryas cooling event, both Earth’s axial tilt variation and Earth’s orbital eccentricity variation presently work to cool Earth’s surface. This natural cooling implies that if human activity brings the weakening of the AMOC and the loss of winter Arctic sea ice mass to their respective tipping points, we can expect a rapid global temperature drop and a rapid onset of a severe ice age.
The latest generation of global climate models establishes that when induced cooling from Earth’s axial tilt variation and Earth’s orbital eccentricity variation reaches a threshold level, strong weakening of the AMOC occurs.10 This induced strong weakening of the AMOC explains why rapid, dramatic global cooling occurs after each interglacial in the past four cycles of the ice age cycle (see figure 5).
Figure 5: Relative Antarctic Temperature Record throughout the Past 400,000 Years in °C Data credit: Robert A. Rohde, Global Warming Art Project, CC-by-SA; Diagram credit: Hugh Ross
Boers ends his paper with a call for more detailed and comprehensive monitoring of AMOC weakening. Such monitoring, as well as detailed and more comprehensive monitoring of winter Arctic sea ice mass, will help us determine how close we are to the respective tipping points and what actions will work best for us to avoid reaching the tipping points. These responses align with the Bible’s creation care mandate for humans to manage Earth and all its resources for our benefit and the benefit of all Earth’s life.
Reasons to Believe emerged from my passion to research, develop, and proclaim the most powerful new reasons to believe in Christ as Creator, Lord, and Savior and to use those new reasons to reach people for Christ. I also am eager to equip Christians to engage, rather than withdraw from or attack, educated non-Christians. One of the approaches I’ve developed, with the help of my RTB colleagues, is a biblical creation model that is testable, falsifiable, and predictive.
I enjoy constructively integrating all 66 books of the Bible with all the science disciplines as a way to discover and apply deeper truths. 1 Peter 3:15–16 sets my ministry goal, "Always be prepared to give an answer to everyone who asks you to give the reason for the hope that you have. But do this with gentleness and respect, keeping a clear conscience."
Hugh Ross launched his career at age seven when he went to the library to find out why stars are hot. Physics and astronomy captured his curiosity and never let go. At age seventeen he became the youngest person ever to serve as director of observations for Vancouver's Royal Astronomical Society. With the help of a provincial scholarship and a National Research Council (NRC) of Canada fellowship, he completed his undergraduate degree in physics (University of British Columbia) and graduate degrees in astronomy (University of Toronto). The NRC also sent him to the United States for postdoctoral studies. At Caltech he researched quasi-stellar objects, or "quasars," some of the most distant and ancient objects in the universe.
Not all of Hugh's discoveries involved astrophysics. Prompted by curiosity, he studied the world’s religions and "holy books" and found only one book that proved scientifically and historically accurate: the Bible. Hugh started at religious "ground zero" and through scientific and historical reality-testing became convinced that the Bible is truly the Word of God! When he went on to describe for others his journey to faith in Jesus Christ, he was surprised to discover how many people believed or disbelieved without checking the evidence.
Hugh's unshakable confidence that God's revelations in Scripture and nature do not, will not, and cannot contradict became his unique message. Wholeheartedly encouraged by family and friends, communicating that message as broadly and clearly as possible became his mission. Thus, in 1986, he founded science-faith think tank Reasons to Believe (RTB). He and his colleagues at RTB keep tabs on the frontiers of research to share with scientists and nonscientists alike the thrilling news of what's being discovered and how it connects with biblical theology. In this realm, he has written many books, including: The Fingerprint of God, The Creator and the Cosmos, Beyond the Cosmos, A Matter of Days, Creation as Science, Why the Universe Is the Way It Is, and More Than a Theory.
Between writing books and articles, recording podcasts, and taking interviews, Hugh travels the world challenging students and faculty, churches and professional groups, to consider what they believe and why. He presents a persuasive case for Christianity without applying pressure. Because he treats people's questions and comments with respect, he is in great demand as a speaker and as a talk-radio and television guest.
Having grown up amid the splendor of Canada's mountains, wildlife, and waterways, Hugh loves the outdoors. Hiking, trail running, and photography are among his favorite recreational pursuits - in addition to stargazing. Hugh lives in Southern California with his wife, Kathy, and two sons.