NEW STUDY FOUND: Possible collapse of AMOC earlier than expected
One of the Earth’s climate system’s tipping points that is of major concern is the collapse of the Atlantic meridional overturning circulation (AMOC). AMOC is part of the ocean’s thermohaline circulation system—that is, the global “conveyor belt” of currents that bring warm water away from the tropics and cold water from the poles. A collapsed AMOC would have huge, devastating consequences for all life on Earth, including the Arctic ecosystem. Until now, the implications of this tipping point and when it will occur have likely been largely underestimated by standard climate models, such as those used by IPCC reports, which had estimated a collapse might occur around 2300 in a high emission scenario.
A newly published study by Ditlevsen and Ditlevsen (2023) comes with shocking results, estimating the timeframe for collapse to be between 2025 and 2095, with a central estimate of 2050, if global carbon emissions are not cut. Evidence of past AMOC collapses stemming from glacier melt during the last Ice Age 12,000 years ago indicates temperature changes of 10°C within a few decades. Other scientists stated that the assumptions about how a tipping point would unfold and the uncertainties in the underlying data are too significant for a reliable estimation of the timing of the tipping point. However, they all agreed that the prospect of an AMOC collapse is extremely concerning and should prompt a rapid reduction in carbon emissions.
According to Stefan Rahmstorf (Head of Earth System Analysis at PIK): “Standard climate models probably underestimate the risk. There are two reasons for that. One, they largely ignore Greenland’s ice loss and the resulting freshwater input to the northern Atlantic which contributes to weakening the AMOC. And their modelled AMOC is likely too stable.”
The loss of the Greenland Ice Sheet is one of the 6 tipping points closest to tipping. Recent research showed that in the first half of July 2023, daily melt estimates have reached a staggering 15 billion tons per day, equivalent to 6 million Olympic swimming pools. If the Greenland Ice Sheet were to melt entirely, it would cause sea level rise of approximately 7.4 metres. Currently, it is the largest contributor to global sea level rise, with a committed 27cm of average sea level rise due to the destabilisation of the ice sheet. The rapid melting of the Greenland Ice Sheet poses a severe threat to communities worldwide, and is a significant contributor to the weakening of the AMOC.
Fresh water from Greenland is pouring into the northern Atlantic Ocean, where traditionally the warm, salty Gulf Stream mixes with the colder Arctic water and sinks before heading south. With the influx of freshwater, however, the warm currents become less dense, thereby slowing the overturn. Consequently, less salt is brought into the region, further decelerating the AMOC. This process is known as the salt advection feedback.
If the freshwater input exceeds a critical threshold, the circulation system can become too slow to be effective or stop entirely. This critical point is referred to as the AMOC tipping point. A collapse of this system would have catastrophic consequences worldwide, reaching as far as the Amazon Rainforest and the ice caps of Antarctica. It would lead to severe disruptions in the rainfall patterns that billions of people in India, South America, and West Africa rely on for their food supply. It would result in an increase in storms and lower temperatures in Europe, as well as sea level rise along the east coast of North America. In the Arctic, the entire ecosystem stands to be affected, from the phytoplankton that form the base of the food chain to the communities relying on a consistent climate for hunting and fishing.
Important to realise is that all tipping points are connected, such as how the melt of the Greenland ice sheet is leading to the slowdown of the Atlantic meridional overturning circulation. Moreover, the tipping of one is likely to amplify others. We realise the results of this new study are very scary and far from comforting. However, it stresses the necessity of immediately cutting our carbon emissions. Businesses, governments as well as individuals. Your actions count. Your actions could help protect all live on Earth.
If you want to know more about tipping points and its consequences, watch our founder Gail Whiteman ‘unpack the polar crisis’.