No climate tipping points

For the set of likely future scenarios we face today, the climate science literature has not identified any approaching global tipping point after which runaway climate change intensifies beyond humanity’s ability to arrest it. While tipping elements of the climate system—like Arctic permafrost thaw and loss of Amazon forest area—do influence total warming, the magnitude of this influence is substantially smaller than the societal factors that will ultimately determine the planet’s climate trajectory.

To you, the reader, the lines above may feel stiff and overly qualified. They, like countless similar sentences in IPCC reports and academic papers, rely on very careful choice of terminology to maintain their accuracy. Yet such care seems increasingly incompatible with a climate discourse that, at times, nurses a weakness for spectacle while trying to satisfy a hunger for clarity about the future that researchers cannot yet provide.

One example that holds fascination for me today, just as it did for my younger novelist self, is the topic of tipping points. More formally called “climate tipping elements,” this subject is a continuously evolving body of knowledge that has been particularly susceptible to confusion and misinterpretation.

Over the years, groups of earth scientists have offered slightly different definitions of tipping elements, and lists of proposed tipping elements have changed with various additions and removals. Tropical monsoons and abrupt changes in the El Niño cycle have fallen out of many lists, while worry over the East Antarctic ice-sheet’s stability is increasing. Meanwhile, research that presents a range of possible climate impacts after global temperatures cross some theorized tipping point often gets summarized by writers and journalists using upper-end, worst-case potential outcomes.

It is not particularly surprising that when arcane scientific detail meets simplistic reporting, it results in a muddle, and it’s a muddle the term “tipping point” itself—evoking an abruptness and immediacy not necessarily characteristic of most, let alone all, tipping elements—perhaps adds to. Climate tipping points and “runaway climate change” are now common parlance in climate conversations, and while different advocates may mean different things in practice when using these terms, they speak to a broadly shared, yet inaccurate, understanding that the climate system is on the verge of very unstable, self-reinforcing, and abruptly rapid disaster.

It isn’t. And it’s important to understand that it isn’t. Taken at rational face value, the feeling that the planet is just years away from sliding beyond a catastrophic point of no return invites unproductive fatalism. At the same time, the perception of an imminent climate cliff seemingly rules out long-term planning in favor of emergency measures, skewing discussion of climate policies in ways that can be counterproductive.

Looking ahead, the key message that the scientific community and climate advocates should reinforce is that humanity will always have chief agency over the climate. There is no tipping point beyond which Mother Earth wrestles control of the whole climate system away from human beings and proceeds to punish us for our sins.

Although the lack of an impending climate cliff may seem to dilute the impetus for climate action, the knowledge that humanity has a decisive hand on the thermostat actually imparts great responsibility upon us. It’s up to us not only to realize a more positive future for humans and nature but also to define the conditions in which we will have to build that vision.

No tipping, no point

In many ways, the term “tipping point” in climate science was predisposed to be misunderstood. Both components of the term invite confusion.

First, the word “tipping” implies the rapidity of an unbalanced cart toppling over. Yet in practice, many climate science papers and reports suggest that rapid changes of state for tipping elements—say, systematic shifts that take just 20 years or less—are rare enough to be the exception, not the rule. Components of the climate system are sluggish on human time scales, and thus many Earth system components change over the course of decades, if not centuries or millennia. For example, future carbon release from thawing permafrost and sea-level rise from loss of the Greenland ice sheet will take place over several hundred years.

To an earth scientist thinking on geologic timescales, that does seem like a very rapid transition relative to the glacial pace at which the Earth system typically changed prior to the industrial revolution. To a layperson who thinks about a stacked pile of blocks or the leaning tower of Pisa tipping over, however, rapid means something different. This discrepancy in perspectives leads to differing expectations for how climate tipping elements behave and how quickly or slowly their impacts unfold.

Second, the word “point,” too, is bound to confuse. It implies a single, precise, known critical threshold beyond which Earth system components tip.

In some cases—and depending on the boundaries one defines for a climate system—that system may indeed behave nonlinearly after crossing an exact threshold. This is the case for a system such as the Thwaites Glacier in Antarctica, a large ice sheet the size of Florida, widely understood to be at risk of irreversible loss of mass over the course of centuries should warming push the ice sheet across a structural tipping point.

However, critical thresholds are rarely precisely known. And large continental-scale systems like Arctic permafrost landscapes or the Amazon rainforest may not possess a single overall climate tipping point, but may instead exhibit nonlinear state shifts at smaller scales in response to crossing regional and local thresholds. Rainforests degrade acre by acre, while permafrost on sunny south-facing hillsides may thaw and release carbon sooner.