Climate ‘tipping points’ are thresholds within the climate system, where small changes in some part of the climate can cause abrupt and perhaps irreversible environmental change.
The scientific concept of tipping points has certainly captured the popular imagination over the last few years – although not almost in the most scientifically accurate way – see the somewhat implausible film ‘The Day After Tomorrow,’ in which a sudden change in ocean currents leads to a new ice age.
It may be that the idea of tipping points have stuck in the imagination because the impacts of fast and unstoppable environmental change on society are potentially huge. This may also be why Sir John Beddington, Government Chief Scientific Advisor, recently met with the UK’s leading climate experts to review the scientific evidence for tipping points, and to discuss their implications for policy.
Examples of potential tipping points are shown in the figure below, and include scenarios such as irreversible melting of the Greenland Ice Sheet, or Amazon rainforest dieback.
Credit: Prof Tim Lenton, from Government Office of Science Tipping Points Meeting.
In a Nature Climate Change article published this week, Dr Tim Lenton of the University of Exeter investigates the possibility that we could develop an early warning system to determine whether we are nearing a climate tipping point.
This would involve watching how parts of the climate system which abruptly change – called ‘tipping elements’ – respond to natural climate variability. Lenton suggests that if these tipping elements begin to change more slowly it could indicate that the climate is becoming unstable, and that we are nearing a tipping point.
Tipping points in the past
Information about how climate tipping points have occurred in the past can be reconstructed by scientists studying chemical, biological and physical evidence in rocks and fossils. But while geological periods of rapid and abrupt climate change have been identified, it can be difficult to work out what caused them, and what exactly happened.
For example there was sudden warming around 55 million years ago when the temperature at the surface of the ocean increased by 4 – 9Ë?C. This event, known as the Palaeo-Eocene Thermal Maximum (PETM), has been linked with rising atmospheric carbon and ocean acidification and is thought to result from the rapid release of a large amount of methane into the atmosphere. However, other theories as to what caused the PETM, which include volcanic activity and large-scale burning of peat having been mooted, and disputed.
Using past climate change to predict the future is tricky because many things may have changed. For example, before the PETM event the planet was considerably different to today – far warmer and with no permanent Arctic ice sheets. So although the PETM is generally considered the closest thing to the current warming of the planet we know about, there are fundamental differences between the two.
Using geological data to predict the future
In spite of the difficulties involved in determining the causes of tipping points of the past, these historical examples might provide a way to test an early warning system.
Many studies of rapid environmental change have been conducted examining the past, some of which have shown tipping elements slowing. These results, described by Lenton as “mixed but encouraging”, might suggest that an early warning system can be developed. It’s early days, but such a system could significantly reduce the risks that tipping points pose.
As Lenton puts it:
“Many people assume that tipping points which could be passed as a result of human-induced climate change are essentially unpredictable. Recent research shows that the situation is not as hopeless as it may seem: we have the tools to anticipate thresholds, which means we could give societies valuable time to adapt. Although these findings give us hope, we are still a long way from developing rigorous early warning systems for these climate hazards.”