In the context of climate science, a tipping point refers to a critical threshold in the earth’s system or related processes which, if passed, can cause sudden, dramatic or even irreversible changes to some of the earth’s largest systems, such as the Antarctic ice sheet or the Amazon rainforest. The resulting socio-economic impacts could be very large, and crossing of one tipping point may then make others more likely to be crossed.
The Intergovernmental Panel on Climate Change (IPCC) AR6 Synthesis Report, published in March 2023, highlights that the likelihood and impacts of abrupt and/or irreversible changes in the climate system increase with further global warming. As warming levels increase, so do the risks of species’ extinction or irreversible loss of biodiversity in ecosystems.
Ice sheet loss
The Greenland and Antarctic ice sheets are supported by land. In a warming world, ice lost from these ice sheets runs into the ocean. This raises sea levels globally, with impacts on coastal communities. The AR6 report states that, at sustained warming levels between 2°C and 3°C, there will be an increase in the rate of loss of the Greenland and West Antarctic ice sheets over the subsequent years and decades. The destabilisation of the West Antarctica ice sheet could lead to an additional metre of sea level rise beyond the likely range of 0.3m and 1m by 2100 (according to the IPCC AR6 Chapter 9: Ocean, Cryosphere and Sea Level Change).
The Amazon rainforest offers a range of ecosystem services, including an important role in regulating regional and global climate. Loss of forest could have various impacts, including risks to regional biodiversity, food security and hydropower generation, as well as potentially amplifying global warming. The Amazon is under a range of anthropogenic (human-induced) pressures, including direct clearance or degradation of forest, as well as climate change.
The forest plays a role in sustaining itself, helping keep regional rainfall at higher levels, by returning moisture to the atmosphere through evapotranspiration, and by limiting fire spread. This means that once a certain level of forest is lost, the resulting drop in rainfall and increase in fire spread may prevent regrowth of that part of the forest, even if all anthropogenic pressures were removed.
The south-south-eastern part of the forest is thought to be at particular risk, due to high human activity in that region. Research published earlier this year in Science provides a detailed review of the drivers and impacts of forest die-back or loss and degradation in the Amazon basin.
Slowdown of the Atlantic Meridional Overturning Circulation
The Atlantic Meridional Overturning Circulation (AMOC) is a system of ocean currents in the Atlantic Ocean that bring warm surface water from the tropics northwards, which cools and sinks at high latitudes, before returning south in the deep ocean. A large weakening or collapse (a very weak state) of AMOC could have devastating impacts, causing cooling in the North Atlantic, large changes in precipitation, shifts in regional weather patterns and large impacts on ecosystems and human activities.
Climate change could weaken the AMOC by reducing the amount of water that sinks at high latitude. Atmospheric warming, and increases in rainfall and ice melt, both make surface ocean water lighter, reducing its ability to sink at high latitude, and weakening the AMOC. Under certain conditions, this weakening may be irreversible, so the AMOC may not recover even if climate change was reversed. The IPCC AR6 report judged that, although a weakening of the AMOC by 2100 is very likely, there is medium confidence that a collapse will not occur.
Research, led by the Met Office’s Dr Richard Wood, stressed the need for more research into such events, which are considered to have a low likelihood of happening, but if they did they could cause very high impacts. Richard’s article presents a novel toolkit to manage the specific risks associated with High-Impact, Low-Likelihood events.
Although we don’t know exactly when a tipping point may occur, we know that the risk of reaching tipping points increases as global average temperatures increase. Reducing greenhouse gas emissions is critical to limiting warming which would help us avoid the worst impacts of climate change including those which could be caused by reaching tipping points. At the same time, we need to adapt to the changes we are already seeing in our climate and the changes that are expected in the coming decades to make sure we avoid the worst impacts.
We will be exploring the topic of climate tipping points throughout September, so follow the
#GetClimateReady hashtag on X (formerly Twitter) to learn more. You may also be interested in registering for our webinar on this theme on 26 September from 15:00-16:00 BST.