It is ironic that the most successful film – in box office terms – about climate change and dramatic changes to the earth was made by Rupert Murdoch’s 20th Century Fox.

It was called The Day after Tomorrow; took about half a billion dollars at the box office; and featured events loosely based on some Mayan prophecies.

Sadly, as paleo-climatologist and professor of earth and planetary science at Harvard, Daniel P. Schrag said: “On the one hand, I’m glad that there’s a big-budget movie about something as critical as climate change. On the other, I’m concerned that people will see these over-the-top effects and think the whole thing is a joke … We are indeed experimenting with the Earth in a way that hasn’t been done for millions of years. But you’re not going to see another ice age – at least not like that.”

Sarah Dry, in her 2019 book Waters of the World, outlined how we came to know more about oceanic movements; what they mean for the earth; and what might happen if there are changes such as the Gulf Stream reversing itself as it has in earth history.

Among the possible outcomes might be the end of one of the few benefits of global warming – the ability of the English to produce drinkable sparkling wine in the south of the country and the move by many French producers to start growing grapes in the area.

However, Dry was describing a risk which was becoming increasingly of concern to scientists whose research can be bundled under the heading of tipping points. The tipping point phrase originated in mathematics and chemistry and means a qualitative change in a system. The scientists are now looking at what that means for our oceans.

The Intergovernmental Panel on Climate Changes used the phrase to describe the critical threshold at which global or regional climate changes move from one state to another.

The problem with tipping points, of course, is that they are hard to predict – both in climate change and the social sciences. Many environmentalists see tipping points as a ‘threshold’ but this is misleading because tipping points can lead to far-reaching non-linear changes.

Gavin Schmidt, NASA Goddard Institute for Space Studies said (PNAS 24 February 2021) that global warming with average temperature rises of at least 1.1 to 3.1 degrees C is probably enough to trigger planetary tipping points and “even with low emissions,” he said.

In a PNAS paper, The quiet crossing of ocean tipping points (2 March 2021), a group of scientists from several countries said: “Anthropogenic climate change profoundly alters the ocean’s environmental conditions, which, in turn, impact marine ecosystems.

“Some of these changes are happening fast and may be difficult to reverse.

“Climate-induced tipping points are traditionally associated with singular catastrophic events (relative to natural variations) of dramatic negative impact.

“High-probability high-impact ocean tipping points due to warming, ocean acidification, and deoxygenation may be more fragmented both regionally and in time but add up to global dimensions.

“These tipping points in combination with gradual changes need to be addressed as seriously as singular catastrophic events in order to prevent the cumulative and often compounding negative societal and Earth system impacts.”

The tipping points can be a caused by a variety of things including deep ocean changes being altered irreversibly.

The authors say: “The upper ocean (upper few hundred metres) mixes on a time scale of decades while the deep ocean water masses are renewed from the surface on a much longer time scale (100 years to 1000 years). The deep ocean can be altered by climate change for thousands of years with the extent of the alteration dependent on the total change of climatic forcing over time.”

Dry’s book explains how the decades of oceanic research have just begun to explain how the deep ocean works and what impact it has on things like the Gulf Stream. The ongoing research indicates that many of the impacts of warming are now ireversible and that some ocean systems are now on the verge of tipping into another state.

The other bit of bad news is that these physical tipping points are not necessarily identical with the way tipping points work with human attitudes.

In another PNAS paper, Predicting social tipping and norm change in controlled experiments (April 20 2021), James Andreoni, Nikos Nikiforakis, and  Simon Siegenthaler say: “A popular theory poses that the pressure to conform to social norms creates tipping thresholds which, once passed, propel societies toward an alternative state.

“Predicting when societies will reach a tipping threshold, however, has been a major challenge because of the lack of experimental data for evaluating competing models.”

The authors conducted a large-scale laboratory experiment designed to test the theoretical predictions of a threshold model for social tipping and norm change.

They found: “In our setting, societal preferences change gradually, forcing individuals to weigh the benefit from deviating from the norm against the cost from not conforming to the behaviour of others. We show that the model correctly predicts in 96% of instances when a society will succeed or fail to abandon a detrimental norm.

“Strikingly, we observe widespread persistence of detrimental norms even when individuals determine the cost for nonconformity themselves as they set the latter too high.”

Although they also find that things which “facilitate a common understanding of the benefits from change help most societies abandon detrimental norms. We also show that instigators of change tend to be more risk tolerant and to dislike conformity more.”

And therein is the political problem. How do you build common understanding of benefits in a polarised society in which the risk tolerant and non-conformists are characterised as mistaken trouble makers by much of the media and the governing party?

John Spitzer drew  the PNAS papers to the author’s attention.