This week we covered tipping points, critical thresholds in the Earth’s climate system. Crossing a tipping point can trigger self-reinforcing, cascading shifts in the behaviour of Earth’s systems that can be irreversible.
Learning more about tipping points at the University of Exeter with Tim Lenton feels like going to the source. The University of Exeter is home to the Global Systems Institute and the Global Tipping Points project, led by Professor Lenton and supported by more than 200 researchers from over 90 organisations in 26 countries.
Doing this module right now is timely as coverage continues of the risk of a collapse in the Atlantic Meridional Overturning Circulation (AMOC), an ocean current that moves surface water northwards towards the Arctic before cooling and sinking to return southward as a deep ocean current. The AMOC is pivotal in regulating climate across Europe and the North Atlantic, but the effects of a collapse in the AMOC would felt globally. More of that later.
Global tipping points have happened throughout Earth’s history. The Great Oxidation Event two billion years ago led to a significant increase in oxygen in the planet’s atmosphere, driving climate change and allowing formation of the ozone layer and the evolution of complex life. It lay the foundations for the atmospheric composition we benefit from today.
We have a range of tipping elements around the world, and crossing a tipping point with one of them could lead to a domino effect where, as Prof. Lenton put it, we’ve “lost control”. Slow forcing can lead to impacts that are felt much more rapidly as systems tip into a new state and more than one tipping point could be crossed with each degree of global temperature increase. As the Amazon is increasingly deforested and exposed to drought conditions, it turns from a carbon sink into a carbon source, emitting greenhouse gases instead of absorbing them. As permafrost melts, it releases large amounts of methane into the atmosphere, accelerating global warming. And as ice sheets and glaciers melt due to global warming, more freshwater is introduced into the oceans, disrupting saltwater current circulation (like the AMOC).
Assessing tipping point impacts is risk assessment – what is the risk, what is the severity and impact of that risk, what is the mitigation, and what does the risk look like after mitigation?
We looked at the early warning signals for tipping points, using the analogy of a waterfall. You are drifting slowly towards the waterfall, you don’t know exactly where it is ahead of you, but you know that it’s out there. So what signs can you see that tell you that you’re about to go over? Warning signals come from analysis of previous events in the same or similar systems, proxy indicators or simulations.
What are the real-world physical impacts of tipping points? In the event of the AMOC collapse, for example, impacts include a dramatic drop in temperature in the UK, Iceland and Northern Europe – of between 5 and 15°C within decades. The viability of agriculture in most of Northwestern Europe is threatened. The effects are felt globally. The growing area for wheat and maize drops by at least half across the planet. The ecology of the North Atlantic is devastated. Tropical rainfall belts move. The Sahel dries. As far afield as New Zealand, warming accelerates.
What are the consequences? Weather extremes, temperature changes, drought and flooding threaten agricultural production. Food prices go up. Food security is threatened. Protests, riots and conflict ensue. Internal displacement and migration increases.
If any of these sound familiar, it’s because they’re already happening. And this underlined a point for me. A tipping point being crossed doesn’t necessarily look like a Roland Emmerich movie. It’s not tsunami waves the height of tower blocks and disintegrating bridges. At least not yet. This plays out in real time, covered occasionally by the news. The tsunami wave isn’t the first thing that hits – it’s preceded by a leading wave; smaller, maybe even a dip in the level of the water. But the collapse of AMOC, if it happens, has been described as cataclysmic.
For many millions, the worst that can happen to them is happening now or has already happened; small island developing states, indigenous communities in the Global South and the world over have lost land, livelihoods, biodiversity, opportunities to grow staple crops, food and water security and connections to ecological, cultural and social systems. They have already passed tipping points from which we’ve been insulated.
The collapse of AMOC isn’t inevitable, the risk isn’t certain. It could occur by 2050 under a high-emissions scenario, or the process could begin later this century, with the effects being felt next century. Nevertheless, the likely impacts if it happens hung over the lecture theatre.
So, what do we do? The group explored options. Systemic change. Food systems change. Policy change. Regulation, by governments, as well as joined-up regulation of TNCs. Degrowth. Taxation of high-carbon industries. Massive, rapid greenhouse gas emissions cuts. Triage and prioritising the worst-affected areas. Media reform. Education and adaptation.
You start to sense the ripple effects of all of these actions, and the potential barriers. It’s felt to me for some time that the scale of the challenge of heading off the worst effects of climate change was larger than practically anybody is willing to admit. It is remaking our society. And it also feels that part of this is about accepting loss – that our climate is going to continue to change, that conditions are going to worsen, and that they may not get better. There is no such thing as prevention now, we’re into the territory of minimising the worst of the impacts of climate change and adapting to a less comfortable future. Why not be radical.
We’re getting into positive tipping points in future sessions.