Credit: Christopher Michel, CC BY 2.0 <https://creativecommons.org/licenses/by/2.0>, via Wikimedia Commons.
Components of the Earth system are expected to undergo abrupt and irreversible changes once global warming has crossed their specific threshold temperature, with mostly negative consequences for human wellbeing.
The scientific debate of such climate tipping points is burdened with high uncertainties, since current climate models are mostly not resolving them and evidence must be collected from different sources, including observations, paleoclimatic records and conceptual models.
Here Jakob Deutloff of the University of Hamburg in Germany discusses his recent research looking at the 16 key Earth system tipping points and the likelihood of their collapse as global warming continues.
ScienceVega: What are some of the key tipping points that you mention in the research?
JD: There are 16 key tipping points and they come from a literature review written by David Armstrong McKay in 2022, which distinguished between the global core tipping elements and those with regional impact. The global core elements are those that affect the whole Earth system if they change, while regional impact ones are more the ones that affect a local community, such as coral reefs for example, where you wouldn’t feel the impacts globally.
One of the key global core tipping elements discussed in the paper is, for example, the Atlantic Meridional Overturning Circulation (AMOC) which is the ocean circulation that also includes the Gulf Stream. If this tips into an inactive state with global warming, then you would expect to see changes in temperature and precipitation globally that would affect a lot of people. It’s a very prominent example.
Then there are the ice sheets such as the Greenland Ice Sheet and the West Antarctic Ice Sheet and the East Antarctic Ice Sheet, which work a bit differently. They are also thought to be tipping points, but it’s more they might already be on a pathway where we can’t stop them from melting anymore, but the melting would take centuries to happen. It is still to be decided whether they will exist in the coming centuries and millennia, or if they are going to melt away. The impact of this would be drastic because you would have tens of metres of sea level rise, but it would be happening over a very long period and that is why sometimes people don’t think they would be that affected.
There are also tipping elements in the biosphere. The two major ones in terms of expected carbon emissions are the Amazon rainforest that could dry and die out, and the permafrost regions which could melt and degrade.
Climate tipping points in the Earth’s climate system. Credit: ESA, CC BY-SA IGO 3.0, CC BY-SA 3.0 IGO <https://creativecommons.org/licenses/by-sa/3.0/igo/deed.en>, via Wikimedia Commons.
ScienceVega: How did you come up with the figure of a 62% risk of triggering these tipping points and is that 62% across all 16 systems?
JD: That’s the average probability across all 16 tipping points. What we did in this study is link the threshold temperature where we think something would tip from an intact state into a disturbed state to emission scenarios. There are ideas as to how emissions might evolve in the coming years based on assumptions made about how society develops and these are called Shared Socioeconomic Pathways (SSPs). There are five SSPs and they range from the best-case scenario (SSP1 – ‘Taking the Green Road’ (very low greenhouse gas emissions) – to SSP5 – ‘Fossil-Fuelled Development’ (very high greenhouse gas emissions)). We linked those scenarios to the threshold temperatures to determine the probabilities of triggering for all tipping elements under the given emission scenario.
When we average the probability of tipping across all 16 tipping elements, we get 62% for the SSP2-4.5, which is the middle of the SSP range. It is the scenario that is most comparable to current policies, which is why we have arrived at this statement. However, the probability of tipping varies a lot between to the individual tipping elements. Coral reefs for example are virtually certain to go, whereas the East Antarctic Ice Sheet will probably not be affected.
ScienceVega: Were you surprised by the results?
JD: Overall, not particularly, but one thing I was surprised by was that when we go from a sustainable scenario, SSP1-2.6, which would be associated with a roughly 2°C warming by the end of the century, to current policies, which would lead to around 3°C of warming, you see a drastic increase in the probabilities of tipping. That tells us that for a rather small emission reduction from current policies to something a bit more sustainable we get a big benefit in terms of reducing the risk for triggering climate tipping points. That was surprising.
The second thing we looked at in this paper was how likely is it that the tipping elements in the carbon cycle, the permafrost and the Amazon, warm the Earth so much that the other tipping elements will be triggered. We found that was rather unlikely, which was surprising, to me at least.
A NASA satellite photo of the Greenland Ice Sheet. Credit: Public Domain.
ScienceVega: Why is it unlikely that the Amazon dieback and permafrost thaw will not cause enough warming to trigger elsewhere?
JD: That is a result of two things. For the lower emission scenarios, we won’t get a lot of global warming and therefore it’s unlikely that we trigger those carbon tipping elements. And because it’s unlikely there’s not a high chance for carbon emissions from them, and therefore there’s not a high chance that they increase the probability of triggering other tipping elements.
Whereas for the high emission scenarios such as SSP5-8.5, all of the carbon tipping elements will go because climate is warming a lot through anthropogenic emissions. However the emissions from the carbon tipping elements are small compared to the anthropogenic ones, so you don’t get a lot of additional warming either.
If we choose to go into a very high emission scenario, the carbon tipping points will go, but it won’t affect us much because it’s small compared to the anthropogenic emissions. If we go for low anthropogenic emissions, the additional emissions triggering carbon tipping points would be substantial, but there’s a low possibility for this to happen.
ScienceVega: What needs to be done to prevent these tipping points being reached or breached?
JD: Simply reduce anthropogenic emissions. When we see the probabilities reduce a lot when we go from SSP2:45, the current policies, to SSP1-2.6, the more sustainable scenario, then this tells us that this is the way we should go. For this we need to reduce emissions in the future more than current policies would lead to.
Bleached coral. Coral reefs have a very low threshold temperature and many may disappear within 50 years. Credit: Danielle.ihde, CC0, via Wikimedia Commons.
ScienceVega: How does that compare with the policies that we’re seeing across the world at the minute in terms of what we’re trying to do, and how far behind are we in doing them?
JD: This is the link I make between the SSP2-4.5 and current policies. It is based on a thing called the CAT Thermometer, a climate action tracker and a website where they track a nation’s determined contribution. It tracks what countries agree to in international negotiations in terms of their emission reductions and if each country implemented all of the pledges that they made, then we would arrive at 2.7°C warming, roughly. That is comparable to SSP2.45.
However, this implies that countries actually keep their promised emission reductions when currently we’re seeing global politics are more on a different route. Climate politics has been falling down the list of other problems. Two years ago, I would have been more positive, but we need more rigorous policies for further emission reduction.
The Amazon River. Credit: Alexander Gerst, CC BY-SA 2.0 <https://creativecommons.org/licenses/by-sa/2.0>, via Wikimedia Commons.
ScienceVega: How close in years are we to triggering any of these tipping points?
JD: That is really hard to say and that’s why we don’t really have it in the paper. We looked at this during my previous master’s thesis, but we didn’t put it into this paper because one piece of information we are lacking is how sluggish those tipping elements are. An ice sheet is pretty sluggish, so you can overshoot the threshold temperature by a little. If temperatures are warmer than we think the threshold temperature is for an ice sheet, but you bring the temperature down quickly again, then the ice sheet might stay intact.
That’s why it is very hard to be certain about timing, but you can get an idea if you look at the internal time scales of these tipping elements. Coral reefs react very fast and they have a very low threshold temperature, so they will probably go within the next 50 years or so. Whereas it could be that ice sheets are triggered anyway, but it will take very long for them to disappear.
A collapsed block of ice-rich permafrost along Drew Point, Alaska. Coastal bluffs in this region can erode 20 metres per year. Credit: Benjamin Jones/ USGS, Public domain, via Wikimedia Commons.
ScienceVega: If a tipping point is triggered, what will be the consequences?
JD: It depends on each individual one, but when you go back to the distinction between regional impact and global core tipping elements, then it tells you that any of the global core tipping elements will be felt worldwide.
These are the three main things: ecosystems are affected, ice sheets and sea level rise, circulation within the atmosphere and the ocean which then leads to shifts in precipitation and temperature. The weather changes quite drastically and this is something humans are not really adapted to.
But I want to stress that there are two ways of looking at this: you can either be negative and say the study finds there is a high probability that current policies will trigger tipping elements; or you could say that it’s still in our hands, that if we go to low emission scenarios then we reduce the probability significantly, and that we don’t see a tipping cascade triggered by carbon tipping elements.
These are both working in a direction where we can still be masters of our own fate in that sense.
The link to the original paper can be found here.
