This article is part of the 4sea Project.
Have you ever wondered how much is actually true about Emmerich’s “The day after tomorrow”-scenario? Can an ice age actually happen with rising temperatures? That sounds pretty paradoxical, right? The most commonly used scenarios in terms of climate change show higher sea level because of increasing temperature and with that, melting glaciers and drowning islands. But there are some other scenarios that resemble Emmerich’s “The Day After Tomorrow” world, admittedly, not quite as dramatic and spectacular as a deep frozen world but there are some similarities.
The Thermohaline Circulation
One major role in this movie is played by the Thermo Haline Circulation (THC), which stops and sets the world back into an ice age. This cannot happen, because the circulation in the Atlantic, including the Gulf Stream, has always been there and will always be? The history of the earth shows otherwise. In the process of warming after the last glacial period around 12000 years ago the THC actually stopped, setting the world back into another small Ice Age.
But how can an ocean circulation just in the Atlantic stop the whole world from warming and set it actually back into an Ice Age?
For that question to be answered it is important to understand the concept of the circulation in the Atlantic. The THC is driven by temperature and density differences in the water column. Warm, saline surface water from the equatorial regions flows northwards to the subpolar North Atlantic. It is transported there by the Gulf stream, a part of the subtropical gyre. The sub-tropical gyre in turn is a wind and coriolis force driven clockwise combination of different currents. The Gulf stream then splits into eddies, meanders and arms and enters the sub polar gyre, again an anticlockwise current in the sub polar north atlantic made out of different currents. Due to air sea surface exchange the warm, saline water is subsequently cooled down and loses buoyancy leading to its sinking. The now denser water masses flow back south in the deep ocean. Some deep water is also formed in the Antarctic where it is distributed to other ocean basins, like the Pacific and the indian ocean. In releasing heat to the atmosphere of the northern hemisphere the THC becomes one of the most important energy sources for europe, next to the sun. It is due to the transport of warm water masses that Europe has such a mild climate , .
The Ocean as a Carbon Sink
But it is not only important for transporting heat to europe, the ocean and the formation of deep water also act as a carbon sink. Due to a constant exchange of gases between the ocean and the atmosphere so far one third of the anthropogenic CO2 has been taken into the deep ocean and stored there . Since we are talking about a circulation these water masses will come to the ocean’s surface eventually but this takes time, and for now the anthropogenic CO2 gets stored in the deep ocean.
So the THC acts as a thermostat for the earth and balances heat distribution in interacting with the atmosphere, meaning that changes in the atmosphere will have an impact on the ocean and vice versa. Changes in the temperature of the atmosphere will also impact sea surface temperature as well as melting of glaciers will have an impact on the salinity of the ocean, since sea ice and land based ice sheets are formed by fresh water. Since temperature and salinity play a huge role for the formation of deep water, changes in former mentioned could also change deep water formation and with that the THC. However, since the THC is hard to measure and variabilities are also occurring naturally it is hard to make any predictions but the past of the earth’s history shows that a weakening or even a stop of the THC is possible.
The day after Tomorrow in the Past
About 12000 years ago, when the world was just transitioning from a glacial period to an interglacial period a huge meltwater lake from the north american continent broke through a barrier of ice and drained into the Atlantic ocean, changing not only the temperature but also salinity content. With the Atlantic changing completely its constitution no warm water could be transported to the northern hemisphere. That led to a cooling of europe and was a start of a little Ice Age called Younger Dryas that lastet for about a 1000 years . Admittedly, it is very unlikely that this scenario could happen today, but still possible, since it already happened. We would not have the same impact as 12000 years ago, still temperatures in Europe would cool down, not to mention the impact on the flora and fauna on land and in the ocean.
About the author: Marie Harbott is studying Marine Geoscience in the North of Germany and writing her Master thesis about deep water formation in the Labrador Sea. She founded 4Sea to draw attention to the Ocean and its importance to the climate system.
This article has been written in the context of 4sea. 4sea, a project about the importance of the world oceans, addresses the interdependence between the oceans and climate change, entraining everyone to become ocean lovers – for now through articles and videos on this blog and in November on our own platform. 4sea is a joint project between the youth organisations CliMates, Youth for Ocean and Vitamin Sea. Love it? Stay tuned for our platform!