Large ice sheets in Antarctica and Greenland, the Amazon Forest, and the Atlantic overturning circulation (AMOC) are believed to be at risk of passing crucial tipping points that could make climate heating spiral out of control.
Tipping points are scary enough on their own. But as it turns out, each tipping point can interact and destabilize each other, causing a domino effect with severe consequences. In a new study, researchers ran over three million computer simulations and found domino effects in a third of them, even under scenarios in which the Paris Climate Agreement targets are met.
“We provide a risk analysis, not a prediction, but our findings still raise concern,” Ricarda Winkelmann, researcher at the Potsdam Institute for Climate Impact Research (PIK) and study co-author, said in a statement. “[Our findings] might mean we have less time to reduce greenhouse gas emissions and still prevent tipping processes.”
The researchers focused on the interaction between the Amazon rainforest, ice sheets in West Antarctica, Greenland and the Atlantic Gulf Stream. They used a new type of climate model that focused on how temperature threshold for the tipping points changed as the systems interacted, allowing them to run the computer simulations.
An example of the interactions is the melting of the Greenland ice sheet. This released water into the ocean and slows down the AMOC – driven by salty water pulled down towards the ocean floor. A weaker AMOC means less heat is transported from the tropics to the north pole, which leads to warmer waters in the Southern Ocean. On the long-run, this could destabilize parts of the Antarctic Ice Sheet.
“The analysis implies that there is still a serious danger of activating cascading climatic tipping points below 2°C of global warming – i.e., in the Paris accord goal range,” Tim Lenton, researcher at the University of Exeter, not involved in the study, told The Guardian. “What the new study doesn’t do is break down the timeframe during which tipping point shifts and cascades might occur.”
Strength in numbers
Observations over the past decades show that several tipping elements are already impacted by global warming — and the more of them start interacting, the harder it will be to stop the climate from rising.
Ice loss from Greenland and West Antarctica has increased and accelerated over the past decades, with studies suggesting that the Amundsen Basin in West Antarctica might in fact have already crossed a tipping point. The grounding lines of glaciers in this region are rapidly retreating, which could induce local marine ice-sheet instabilities and lead to the disintegration of the entire basin.
It has also been shown that the AMOC experienced a significant slowdown since the mid 20th century, which has led to the weakest AMOC state in centuries. While so far it has been largely caused by changing surface buoyancy fluxes, in the future the strength of AMOC could be impacted by increased freshwater forcing of the North Atlantic Ocean.
At the same time, the Amazon rainforest isn’t just directly impacted by anthropogenic climate change (including the increased risk of extensive drought events or heat waves) but also by deforestation and fire. This increases the likelihood that parts of it will shift from a rainforest to a savannah state. The Amazon could be close to a critical extent of deforestation, which would be sufficient to start that transition.
The study was published in the journal of the European Geoscience Union.