The Gulf Stream brings warm water from the Caribbean to the Norwegian coast, as has been the case for thousands of years. What exactly happens when that power – known as Amoc – ceases is a matter of debate. But all the suggested possibilities have one thing in common: a severe blow to current life on Earth. When that flow can be stopped, it is of great interest to humanity.
But what can reasonably be said about this? Not much at the moment, conclude the researchers involved in the ClimTip research programme, which was created especially to map these climate tipping points. They looked at what happened when the uncertainties of a climate model created for such predictions are taken into account. The result was that Amoc will probably stop sometime between the year 2050 and the year 8065.
Data gaps
These unusable predictions are not inherent to Amoc, the researchers say in a journal article. Scientific advancesUncertainties apply whenever one attempts to say something based on past data about the timing of such a change by large “Earth systems”, such as the Amoc, the rainforest, or the ice around the poles.
The fact that the Earth is experiencing a threatening warming as a result of CO2 emissions can be measured and predicted fairly well. It is the disastrous effects, when ecosystems collapse irreversibly, that are harder to capture in models.
This is largely due to gaps in the historical data we have, says Niklas Boers, coordinator of ClimTip and one of the authors of this study. But the assumptions on which the model is based also lead to a great deal of uncertainty. As does the relationship between said Earth system and the values with which we measure that system. We “see” the Amoc, for example, by measuring differences in water temperature, but that doesn’t mean that those measurements also describe the system well.
Small differences lead to completely different results
By its nature, a tipping point is extremely difficult to predict because it is not gradual. Compare it to a water faucet that you keep turning on. At some point, the flowing stream of water will turn into a spraying jet. That prediction can be made from experience. But it is incredibly difficult to predict exactly how far the faucet must be turned on to reach that tipping point.
Of course, this is even more true if the “water tap” in question is a terrestrial system that extends over thousands of kilometres. There are a great many factors at play, and minute differences can lead to completely different predictions about the tipping point. And precision over all of those factors is still a long way off, Boers concludes.
You just have to look at historical data, which is used to track a trend. “We have good satellite measurements now, but they are only available from the 1980s. If we have satellite data for the last 250 years, I am all for it, but we will have to wait a long time. That is a pretty fundamental problem.”
We don’t understand it, which calls for even more caution.
These uncertainties add up and reinforce each other, which in Amoc’s study led to an unusable uncertainty margin of six thousand years. Boers is certainly not the first to warn about the huge uncertainty in current forecast models. It is a “prospectus” commonly used in such studies, although it is not always clearly communicated. Boers sees a risk in this: “If we say we can predict such tipping points, we give the impression that we understand these systems, which is clearly not yet the case. And if you don’t understand it well, you have to be much more careful.”
At the same time, the question of when this tipping point will be reached remains absolutely relevant, Boers stresses. According to him, the best way to achieve greater accuracy in such a prediction is to focus on better models. “We have to work on translating all the knowledge about such a system into computer code, to arrive at an approximation of how it works. We will certainly make progress in this direction, but that also takes time.”
What we can say with certainty in the meantime is that the risk is increasing: “The probability of vital parts of Earth’s systems reaching a tipping point increases with every tenth of a degree of warming.”
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