Possible irreversible changes in subsystems before reaching climate change tipping points

Recently, two researchers from the University of Copenhagen published an article in the Proceedings of the National Academy of Sciences describing their work on the possibility of changes to the Atlantic Meridional Reversal Circulation (AMOC) and the circumstances that could lead to such changes. In their paper, Johannes Lohmann and Peter Ditlevsen noted that climate models show that irreversible changes in subsystems such as AMOC, one of Earth’s global subsystems, can occur before a point of tipping if changes are occurring at a rapid pace.

They further noted that the fresh water flowing into the Atlantic Ocean due to melting ice could cause such an irreversible change. More recently, an international team of climatologists published a Perspectives article, also in PNAS, describing the damage that could result if irreversible changes occur before tipping points, and also what models suggest will happen if Earth begins to reach certain tipping points.

In climatology, tipping points are climatic milestones that occur when changes are made to the global ecosystem that result in other permanent changes. If too much carbon dioxide is injected into the atmosphere, for example, at one point, it will become too hot for animals to survive. Climate models suggest that in such scenarios there is no turning back. Once a tipping point is reached, we cannot solve the problem by stopping carbon emissions. More recent research has suggested that there may be pre-tipping points that could trigger smaller-scale climate change, but which are still irreversible. Cool, cold water entering the North Atlantic, for example, could cause permanent changes in AMOC. In particular, AMOC is responsible for the mild temperatures in Europe.

In their article, the authors of the Perspectives article describe the likely outcomes of different scenarios that could lead to subsystem changes before the tipping point. They note, for example, that the world’s oceans include subsystems. In addition to rising sea levels, the world’s oceans are undergoing acidification from carbon dioxide absorbed by the atmosphere. Acidification harms marine life. Additionally, previous research has shown that the upper part of the ocean absorbs heat from the atmosphere at a much higher rate than the lower regions. The lower regions are just beginning to feel the effects of warming, a long-term event that could change the entire underwater ecosystem – a change that would be irreversible.

The good news is that the AMOC study researchers and the authors of the Perspectives article all agree that it is not too late to prevent such scenarios from unfolding. Whatever is needed to stop greenhouse gas emissions, and then for scientists to focus their energies on the parts of the planet that have already been damaged.

© Science X Network 2021