Two Degrees Too Many: Average Global Temperature Increase Will Trigger Climate Tipping Points

In September, the journal Science published a study where lead author and climate scientist David Armstrong McKay and his co-authors outlined an updated list of crucial climate tipping points. Mountain glaciers were named a tipping point for the first time in this article, along with several other changes.

The paper defines climate tipping points as specific conditions that lead to irreversible and dangerous impacts for Earth systems and consequently for humanity. Not only do these tipping points come abruptly, but they also become self-perpetuating once surpassed. The 1.5 degrees Celsius threshold became prominent in 2010, and it has since been considered the upper limit of warming Earth can endure before the effects, specifically those of triggered tipping points, become irreversible.

The article states that for an environmental shift to be considered a tipping point, it must meet five criteria: self-perpetuating change, irreversibility, abruptness, spatial significance, and substantial impact. First, self-perpetuation is loosely defined as the continuation of change in a system after the changing force no longer exists. Second, irreversibility refers to the unchangeable and substantial impacts of an environmental change, though the authors acknowledge the possibility of a few exceptions for reversible tipping points. Third, the authors follow the IPCC in generally considering abruptness to be change that occurs substantially faster than the rate of change in recent history. Fourth, for a tipping point to be considered spatially significant, it must be a part of Earth’s system that is subcontinental or larger in size. Finally, substantial impacts encompass a vast array of possibilities, including but not limited to: affecting human well-being, notably affecting Earth’s systemic operation, or maintaining inherent value as a part of the Earth’s system. 

In 2008, nine global tipping points were identified. The 2022 paper includes these original nine, ranking the threat of each and the early warning signs they would bring. In addition to expanding on these nine tipping points, the recent paper also outlines specific outcomes that would result from 1.5 C warming, between 1.5 and 2 C warming, and between 2 and 3 C warming. The 2015 Paris Agreement deemed an average global temperature increase of 1.5 C to be the benchmark to considerably reduce the effects of climate change. 

The study predicts that 1.5 degrees warming would trigger these tipping points: the collapse of the Greenland Ice Sheet and the West Antarctic Ice Sheet, die off of low-latitude coral reefs, abrupt thaw of the boreal permafrost, and possibly the abrupt loss of ice in the Barents Sea. Surpassing these tipping points would drastically alter ocean circulation, causing a significant redistribution of heat in the oceans and atmosphere. Along with habitat loss, decreases in biodiversity, and increases in hazardous events, the triggering of the first round of tipping points would only worsen conditions, likely setting the next round of tipping points in motion soon after. 

The second round of tipping points set off from 1.5 to 2 degrees of warming includes mountain glacier loss, which is the first mention of glacier loss as a major tipping point. Glacier melt rates have been severe for some time now, but global temperature increases pose the possibility that almost all mountain glaciers could disappear. Glaciers play a primary role in water supply and sea level regulation, and total melting would worsen floods and land disappearance already occurring across the globe. 

In discussions of tipping points, the origins of the phrase itself often go undiscussed. Though “tipping point” is a term that spurs concern and action, its origin could be seen as problematic by many. The phrase originated in the 1950s, when it was used to describe the percentage of white families in cities in the US who were inclined to move out of a particular area when Black families began to move in; surpassing the “tipping point” often caused a mass exodus of white families from the area. The term has evolved and is presently used in primarily environmental contexts, but its use perpetuates the systemic racism that remains intertwined in issues of climate justice. 

The consequences that may occur if all tipping points have been surpassed are both imminent and dire. To date, anthropogenic greenhouse gas emissions have caused a 1.1 C increase in global average temperature. Despite increasingly ambitious emissions reductions goals, like the United States’ goal to hit net zero emissions by 2050, temperatures are still projected to surpass 1.5 degrees of warming in the coming decades; these changes will have the most impact on countries with the smallest contribution to the problem, and many currently lack the infrastructure necessary for adaptation to an altered climate. Continued research on tipping points provides a better understanding of what comes next in almost every scenario, promoting both preparation and mitigation.