Blog

Potentially catastrophic tipping points may be much closer than we thought

Scientific reports describing the dangers of climate change are now so frequent that unless you track the relevant journals carefully it’s easy to miss something really significant. A study published September 9th in the journal Science is easily among the most dramatic and worrisome I’ve read in many months.

The new analysis updates our knowledge of tipping points, abrupt and potentially irreversible changes in the earth’s climate system with grave consequences. Multiple such possibilities have been discussed by scientists for more than two decades and were among concerns responsible for the Paris Agreement aim to limit warming to well below 2 °C (3.6F) and ideally to 1.5 °C. The number and consequence of tipping points is now thought to be much greater than originally thought.

The authors, ten leading climate scientists from the U.S. and Europe, assessed more than 200 previous studies on past tipping points, climate observations and modelling. They reviewed the evidence for 16 distinct tipping points, nine global “core” tipping elements which contribute substantially to Earth system functioning such as the collapse of several enormous ice sheets with the potential to raise sea levels several meters or more. The team of authors also assessed seven regional “impact” tipping points which could threaten human systems with great value.

Their dramatic conclusion is that the trigger for five tipping points, including collapse of the Greenland and West Antarctic ice sheets, die-off of low-latitude coral reefs, and widespread abrupt permafrost thaw may already have been reached by the current 1.1C warming above pre-industrial levels. Six more become likely within the Paris Agreement aim to limit warming to 1.5 to <2°C. Yet more become likely at the 2 to 3°C of warming expected on the basis of current policy trajectories. And every increment of warming increases the odds of crossing some threshold.

There is also the possibility of cascading effects of yet greater complexity and uncertainty but a source of additional danger. For example, melting from the Greenland ice sheet would release freshwater into the ocean and slow the Atlantic circulation, resulting in further warming of the oceans and more rapid melting of the Antarctic ice sheet.

While a significant contribution, our understanding of tipping points continues to be imprecise as to timing and consequences. The lead author of the study, David A. McKay, described the results as “grounds for grief” but also for hope. “We’re not saying that, because we’re probably going to hit some tipping points, everything is lost and it’s game over. Every fraction of a degree that we stop beyond 1.5C reduces the likelihood of hitting more tipping points.”

In the understated language of scientists, the authors conclude: “This strengthens the evidence base for urgent action to mitigate climate change and to develop improved tipping point risk assessment, early warning capability, and adaptation strategies. While other scientists point to the limitations of current knowledge and need for further study, the message is clear — failing to limit global warming could have multiple disastrous consequences and much sooner than we thought.”

The new assessment adds to our understanding of climate risks but of greater importance to the sense of urgency regarding the need to rapidly reduce greenhouse gas emissions and particularly methane. We know from analysis published earlier this year that even dramatic reductions in CO2 will not slow warming until after 2050 due to the simultaneous reduction in short-lived sulfates, a source of cooling. The only way to keep warming below well below 2 °C for the next two decades and avoid dangerous tipping points is by reducing methane and other climate pollutants with short atmospheric lifetimes. Targets for “net zero” and reducing emissions by 2050 are too late — the time for aggressive action is now.

Alan Miller is a former climate change officer in the International Finance Corporation (2003–13) and climate change team leader, Global Environment Facility (1997–2003). Besides other engagements, Alan is an active editor for Climate Conscious submissions on Medium.