Could Global Warming Lead To Catastrophic Freezing?

In response to global climate change, other systems, such as global oceanic circulations, could collapse, with devastating consequences.

When it comes to battling climate change, some people think that the only issue we may be facing is that the climate may get a few degrees warmer. And, of course, if you live in rather cold areas on Earth, you wouldn’t mind some extra warmth. Even if you live in a temperate region, you may be inclined to think that 1.5 to 3 °C may not be such a big deal after all.

But there is much more to climate change than warming temperatures. For example, in a previous story, I talked about how, by studying fossil records, we discovered the catastrophic chain of events following increased greenhouse gas emissions and global warming. The list goes on and on, from ocean acidification and anoxia to droughts and mass extinctions.

What if I told you that the current global warming, with its associated melting of the ice sheets, could trigger a chain of events driving us in the opposite direction? I am talking of a cooling event 15 times faster than the warming we are now experiencing.

We must understand that the Earth is a balanced system where anything may tip the balance and trigger a long chain of harmful events. As scientists, we incorporate all of these tipping elements in our models and corroborate this data with information from the past. One of the elements that got special attention recently was the tipping point of the Atlantic Meridional overturning circulation (AMOC).

According to NOAA (National Oceanic and Atmospheric Administration), “AMOC stands for Atlantic Meridional Overturning Circulation. The AMOC circulates water from north to south in a long cycle within the Atlantic Ocean. This circulation brings warmth to various parts of the globe and carries nutrients necessary to sustain ocean life.”

A recent publication in the prestigious peer-reviewed journal Science Advances brought the alarming news that the AMOC may be on the edge of collapsing.

The AMOC has been continuously monitored since 2004 when scientists understood its implications for local and global climate patterns. Again, the past offered clues about the importance of these ocean currents. Using ice cores and ocean sediments, scientists observed that 12,000 years ago, following a massive glacier meltdown, the AMOC completely shut down. We have a past referent, but could this happen again? And if so, what would the consequences be?

Using a supercomputer, René van Westen and their team run a complex computer model simulating a gradual increase of freshwater to the AMOC. This model was so computer-intensive that it took three months to run to completion. Usually, the more data and variables a model considers, the longer it takes to complete, and this simulation was the most comprehensive of its kind to date. Besides calculating ocean circulation as a response to adding freshwater from melting glaciers, it also calculated temperature and precipitation worldwide.

The authors observed that after enough fresh water was added to the modeled system, the AMOC completely collapsed. According to the model, the collapse will occur with less fresh water added to the ocean than we previously thought. In fact, another controversial study from July 2023 pointed out that this tipping point could be reached by the middle of this century.

The scariest part of this study is the potential consequences for Earth’s climate if the AMOC were to suddenly stop after already showing signs of slowing down. What would these changes look like? Let’s look at the figure below.

According to the model shown in the figure above, winter temperatures (continuous lines) decrease by 5°C, summers become drier, and precipitation increases during the winter in North America. The Amazon takes the most significant change, with dry and wet seasons completely reversing, albeit with a decrease in average precipitation. Since Amazonian vegetation is adapted to the current precipitation regime, this could completely disrupt food productivity in the region, which is necessary for global food supplies.

Northern Europe becomes drier overall, and winter temperatures fall by over -20°C. Central Africa and South East Asia reverse their dry and wet seasons, as seen in the Amazon. And although temperatures stay similar in Australia, its precipitation regimes flip entirely. The authors point out how the observed changes occur within a relatively short period (10 years) and after a reasonably low addition of fresh water to the system.

Additionally, the authors point out that the tipping point calculated in this study is “consistent with the wealth of paleoclimate evidence that rapid changes have occurred in the AMOC.” In other words, a computer-driven model shows the same results observed in the fossil record, reinforcing that past events can inform future climate changes and serve as control scenarios.

Among their most remarkable results, however, the collapsing of the AMOC may dramatically redistribute heat (and salt), resulting in a cooling of the Northern Hemisphere and a slight warming of the Southern Hemisphere. They observe a rapid cooling of the European climate with more than -3 °C temperature trends per decade. To put this in perspective, the present-day global mean temperature change due to global warming is +0.2°C per decade. The model also suggests a rise of up to 70 cm in sea level. How would the world realistically adapt to such rapid change?

The authors refrain from hypothesizing an actual point in real time when the tipping point could be reached. Their model uses an environmental simulation that starts under preindustrial conditions. During the simulation, they kept greenhouse gas, solar, and aerosol forcings constant to preindustrial levels. They do this to investigate the effects of a single change (adding fresh water from melting ice to the system) on global ocean circulation. The model gives them an estimate of the amount of freshwater necessary to tip the system rather than the exact point in time when this may occur. However, they suggest adding these variables in future models.

Additionally, the model points out that the current postindustrial amount of fresh water in the system brings us closer to this AMOC tipping point than we’d like. Creating an even more complex model incorporating all the uncertainties about climate change could give us a more accurate answer on timing. Hopefully, machine learning and modeling technology will get us to the answer before we reach the AMOC tipping point.

To cover this news, CNN interviewed Dr. Jeffrey Kargel, senior scientist at the Planetary Science Institute in Arizona, another scientist who didn’t participate in this most recent discovery but is an expert on the topic. This is a widespread practice among science journalists for major news outlets. To understand the implications of a particular study, they interview other experts who may or may not have differing interpretations of specific research results. I have been interviewed in similar situations before.

Quite remarkably, Dr. Kargel points out that, while models about AMOC are somehow controversial and indicate different timings, our skepticism may as well be gone once we “know it is happening” already. As he points out, the big issue is that, with so many variables considered, we may fail to predict which change is irreversible, leading us to the feared outcome of total collapse.

As previously stated here regarding the Amazon Tipping Point, as Thomas E. Lovejoy and Carlos Nobre wrote, “There is no point in discovering the precise tipping point by tipping it.” Indeed, we don’t want to find out we have gone too far by having all our systems collapse.