Climate Tipping Points Are Coming, But We Lack The Capacity To Tell When

As the Earth warms, it could cross several so-called tipping points that would turn the effects of climate change from disastrous to catastrophic for most of the planet. Naturally, many scientists have put a lot of effort into trying to find out how close we are to these points, but a new study claims we simply don't know. There is too much uncertainty to tell whether those tipping points are close or many billions of tonnes of carbon emissions away, the authors conclude, making caution a priority.

Complex systems – of which the climate is certainly one – can shift from one relatively stable state to another, at which point it becomes very difficult to return. A common example is when rainforest dries out to the point it becomes first dry open woodland, and then savanna. Even if the wet conditions that previously sustained the forest return, the rainforest will not (without additional inputs, which are often quite large).

Many tipping points are local, but a few of global significance have haunted climate scientists for decades. Most or all of the Amazon Rainforest experiencing the shift described above is one. Some of the planet's glaciers retreating past certain hold points is another. The accelerated melting of tundra permafrost and ocean methane hydrates and the collapse of the Atlantic Meridian Overturning Circulation (AMOC) are the others that draw the most attention, although the collapse of stratocumulus clouds is also lurking.

We know these have all tipped before, and in many cases have witnessed smaller counterparts do it in recent times.

If we added enough greenhouse gasses to the atmosphere, all of these would probably happen, and life would become unbearable for most of humanity. According to the study authors, however, we have little chance of knowing what would be required to trigger each.

The scientists conclude there are three main sources of uncertainty in our estimates of what would trigger each tipping point.

For one, our models of the physical mechanisms behind the tipping points are at least somewhat simplistic and may not fully capture the reasons past tips occurred. In addition, our observations of the relevant systems may not always be as representative as those making models of these systems assume.

Finally, historical data – both from direct observations and from climate proxies such as tree rings – cover only a fraction of the locations and times needed to understand past behavior. Efforts to fill in the gaps statistically are not as reliable as some researchers think.

The authors delve more deeply into AMOC as an example of widespread challenges. A previous study concluded AMOC will collapse between 2025 and 2095 if carbon emissions continue at projected rates. Seventy years is a wide margin of error, but the researchers don't think even this is enough. They show there are at least three methods to predict when AMOC – which helps keep northern Europe warm – and the entire ocean current system might collapse. Using all three, rather than just one as others have done, but with different starting assumptions, they conclude such a disaster could occur any time between 2050 and 8065. Even that broad range assumes we have the underlying causes of past collapses right, which may not be the case, and on one modeling method, AMOC might not tip at all.

“Although some of the quantitative results of this work are specific to the AMOC, we show that these types of uncertainties will be present in any attempt to extrapolate a future tipping time of proposed Earth system tipping elements from historical data,” the authors write.

"Our research is both a wake-up call and a cautionary tale," lead author Maya Ben-Yami said in a statement . "There are things we still can't predict, and we need to invest in better data and a more in-depth understanding of the systems in question. The stakes are too high to rely on shaky predictions."

Inevitably, some will take this as a license to keep on polluting, but co-author Professor Niklas Boers argues the opposite. “We still need to do everything we can to reduce our impact on the climate, first and foremost by cutting greenhouse gas emissions. Even if we can't predict tipping times, the probability for key Earth system components to tip still increases with every tenth of a degree of warming,” he said.

On the other hand, the work should act as a counter to those who argue it is already too late to stop climate collapse, and we should either abandon society or party for the few years we have left.

The study is published open access in the journal Science Advances .