Will the earth’s climate reach a tipping point beyond which the planet will become a ‘hothouse’? It’s a possibility scientists warn of in an article that’s urgent reading.
‘The article, in the “Perspectives” section of the PNAS, doesn’t report any discoveries,’1 cautions Michel Crucifix, a professor and FNRS senior research associate at the UCLouvain Earth and Life Institute, ‘but it is a warning based on a synthesis of our knowledge of ancient climates, possible climate tipping points and when we might reach them.’
Initiative for the publication came from the Stockholm Resilience Centre, which, as its name suggests, studies the resilience of ecosystems. If they’re disrupted, will they regenerate or die? The article expands the question to the entire earth, conceived as a single gigantic ecosystem with multiple components that interact: Amazon rainforest, ice caps, oceans, deserts, etc. What would happen if the system becomes too disrupted, if points of no return, or tipping points, are reached? This is the general context of the article.
But first, what do we mean by a tipping point? In other words, what are the risks to the system that should be taken into account? ‘Ten years ago,’ explains Prof. Crucifix, ‘we began to talk about the possibility of a collapse of the Amazonian forest, that is, its transformation into savannah. It’s a possible risk owing to climate change. Another, more likely, possibility is the irreversible melting of the ice caps. Of course, the ice will not disappear in ten years, but we can pass a critical threshold beyond which collapse becomes unavoidable, it’s a point of no return. Another example is the melting of permafrost. All these events are tipping points.’
Physicists are interested in studying dynamic systems, that is, those that include an object that can be moved from its centre of equilibrium; pendulum and spring are a good example. The same goes for the climate: a force – the anthropogenic disturbance driven by greenhouse gas emissions – is exerted on the system, and the system’s response – rising temperature – requires study. But, as any physics student knows, there may come a time when the system is no longer linear (proportionality ceases to exist between the exerted force and the result it produces): pull too hard on the spring and it will break. ‘In such a case,’ Prof. Crucifix says, ‘the equations that were used to describe the phenomenon no longer work. This is the idea of a tipping point, a breaking point: the equations being used usually cease to be correct. It’s often synonymous with bad news.’
A 3° C increase
What’s the current situation? It’s now accepted that in the event of a doubling of the concentration of CO2 in the atmosphere, the average temperature at the surface of the globe will increase by 3° C. This doubling is to be calculated from the pre-industrial situation, when the CO2 content was 280 parts per million (ppm); the current concentration is about 405 ppm, which computes to an increase since 2000 of 20 ppm per decade. Since 1970, average temperature has increased at a rate of 1.7° C per century. This data tells scientists that it is indeed possible to reach the 3° C (we are far from the 2° C objective of the Paris Agreement).
But, after all, is it serious? Let’s take a quick tour of the past. Over the very long term, the climate system follows a glacial-interglacial cycle: hot period, cold period, hot, cold...this is the normal cycle in the absence of any human intervention. A glacial period – and this is one of Prof. Crucifix’s contributions to the article – requires a CO2 concentration under 300 ppm. ‘We must therefore conclude that a glacial period will not occur again for a long time, that’s an established fact. We’re no longer in the “natural” cycle.’ The ‘warm’ climate of the Holocene (which began about 11,700 years ago) was very favourable. We developed our civilization and changed our environment. ‘Would a world of only dinosaurs be better? We’re not here to make such comparisons. And we can say that a world without glaciation, with a climate like the Holocene, which would last another 100,000 years, is really not deadly.’ But we’re unfortunately not in this situation: over the last 7,000 years, the rate of increase in temperature has been only 0.01° C per century. Compare that with the rate of 1.7° C per century since 1970.
The article’s fundamental question is: How can we avoid entering the much more unpleasant world that lies beyond the tipping points? Prof. Crucifix says, ‘We came out of what we call the “icehouse” [the Ice Age] with the risk of entering a hothouse, a much less hospitable earth. Since we’re doing nothing about it, we’re likely already rapidly on our way.’
Beyond temperature threshold logic
So it’s out of our hands? ‘No’, Prof. Crucifix says quickly. ‘But we must get beyond this logic that simply sets an average temperature increase threshold that must not be exceeded. In your home, you have a thermostat that monitors parameters, and decisions are made based on what’s observed. It must be the same for the earth, so you need a way to monitor the possible tipping points and make decisions based on what you observe.’
This will only be possible under three conditions. The first is that you have to understand how tipping points work. What is the probability of reaching them? What are the warning signs? This entails research. Second, continue and intensify observations. Finally, global governance is required to take warning signs into account. ‘The first to pay the price will be the most vulnerable people, those with low incomes. This is the business of the UN, especially since no state will pursue initiatives that penalise its own economy. We advocate for this very strongly in the article, which is why we chose climatologists but also social and political science specialists to contribute. We’re probably sending this message with great naivety, but that’s our role.’
If the climate was only a physical system, the solution would be simple, and it’s actually among those required today: reduce emissions, stop disrupting the system, then it will rebalance itself. But this is not enough insofar as societies cannot be asked to change their economy without being provided the means. ‘So reduce, yes,’ Prof. Crucifix says, ‘but it will only happen if accompanied by economic solutions. We propose solutions to regulate the link between natural resources and economic activity. I’m convinced that we will exceed 2° C and reach 3° C. We must stop fantasising, because it’s certain we’ll continue emitting CO2. It’s necessary to satisfy the energy demand of countries like China and India, soon Africa. Setting a ceiling of 2° C, arrived at basically via the Coué method, without rethinking the economy is a mistake.’
The strategy must be recast through what the authors call deliberate management. This involves designing an economy where natural resources will be managed in a systematic way, and the management of tipping points, exhaustible resources and particularly warning signs will be the basis of global governance.
Disturbing the climate system, per se, is not a problem. The problem is not implementing a system to inspect and monitor the disturbance. The problem is not recognising that we have moved beyond a time when, as hunter-gatherers, we could use resources made available to us, to another time when we must manage the link between natural resources and human communities.
(1)Trajectories of the Earth System in the Anthropocene, Will Steffen et al. PNAS August 6, 2018. 201810141; published ahead of print August 6, 2018. https://doi.org/10.1073/pnas.1810141115
Short bio of Michel Crucifix
1998: Bachelor’s Degree in Physics, University de Namur
2002: PhD, supervised by André Berger, on glacial-interglacial cycle modelling, UCLouvain
2002-06: Palaeoclimate Research Officer, UK Met Office, Hadley Centre for Climate Change, a research centre created in 1990 by order of Margaret Thatcher
2006: FNRS Research Associate and Part-time Associate Professor, UCLouvain
2015: FNRS Senior Research Associate and Professor, UCLouvain
2015: Member, Royal Academy of Science, Letters and Fine Arts of Belgium
His research focuses on the variability of the climate system, mainly at the Quaternary (Ice Age) scale.