Small Changes in Temperature Matter — Probably More Than You Think


A recent episode of the Sam Harris podcast featured Joe Romm of ThinkProgress. Overall it was an excellent episode that over the course of two hours unpacks the scientific case for climate change like only Romm can.

We move from the obligatory — how we know humans are responsible — to how we course-correct — what I refer to as the “hard problem” of carbon mitigation. Romm importantly emphasizes that because we are to blame, we thereby hold the keys to the kingdom so to speak in terms of also being the solution. After all, the knowledge that our activities are behind the climate crisis entails the insight that scaling back or modifying those specific activities will reverse the damage already done. The ‘climate change is natural’ camp have no such insight on offer.

Speaking of uninformed palaver, he also takes on some of the common misconceptions and arguments parroted by think tanks and the uninitiated legions who spread them (with a shout-out to Skeptical Science). Finally, he covers the historical ground surrounding this debate and why it’s existed largely outside the scientific sphere.

How Much Is Too Much?

One point Sam raised that could have benefited from a more comprehensive response is the popular notion that ‘the planet has only increased in temperature by a few degrees, and hence is that really cause for concern’? The misconception here is that a few degrees constitutes a “small change in temperature.” It doesn’t.

This intuition likely draws from our local conception of temperature. In the city or town where you live, it may vary by 20 degrees or more in a single day. What does this tell us about climate change? Not very much. When we talk about climate change, we’re not talking about daily variation in a single spot on the globe, but about the average temperature trends of the globe as a whole. As the mean temperature of the planet moves steadily in one consistent direction, meaningful changes to the environment begin to occur in ways that just looking at a day-night cycle in Vancouver would miss out on.

So how much global temperature change matters? To answer this question, we need to know something about how climate has changed in the past (paleoclimatology). The first thing we learn from looking at historical variation is that it takes a pretty strong influence to tip the earth’s thermostat in either direction. Outside of major events like ice ages and sustained bursts of volcanic activity, the planet has tended to stay within a fairly tolerable range. For the last 7,000 years or so, sea levels have stabilized, and global temperatures haven’t moved more than plus or minus half a degree Celsius — up until recently. It’s probably not an accident that human civilization as we know it developed during this interval.

Even in the case of episodic events it can take a relatively long time for sizable changes in global temperature to manifest. Let’s take ice ages, the records of which leave their mark on proxies like ice cores and oxygen isotope data. A full ice age transition from a glacial maximum to the subsequent interglacial will typically undergo a total change of around 4-6 degrees C, and play out over the course of 5,000 years or more. In contrast, our instrumental records report a gain of over 1 degree (1.1° Celsius or 2.0° F) in a single century, with two-thirds of that increase occurring only since 1975. This equates to roughly ten times the background rate of ice age-recovery warming. Small changes in global temperature matter, as does the rate at which they unfold.

Another high-stakes event, occurring 56 million years ago and known as the Paleocene-Eocene Thermal Maximum (PETM), unleashed a total warming of between 5-8 degrees C, or as much as 16 degrees F. The prodigious release of carbon, and the associated rapid rise in temperature that resulted, transpired over the course of at least 8,000 years, or 15 times slower than the current rate of carbon release from anthropogenic outputs. A more recent study by Gutjahr et al 2017 corroborates these findings with ocean sediments, showing that a rate “of up to 0.58 petagrams of carbon [were] released each year over 50,000 years. About 10 petagrams of carbon are currently released every year from fossil fuel emissions.”

While the underlying causes of this unique period in climate history are still being sorted out (the latest evidence points to an uptick in volcanism), we can look at the effects of those causes in terms of the climate and planetary ecology and habitability. The PETM carbon perturbation led to massive ocean acidification that resulted in the largest deep-sea extinction event in the last 93 million years, killing off approximately 35-50% of all benthic (bottom-feeding) species. It took more than 200,000 years for the earth’s systems to recover, including 100,000 years for the oceans to rebalance.

We’re already seeing measurable impacts to ocean chemistry and marine biology from anthropogenic activities over the last few hundred years. All of the carbon the oceans have absorbed since Industrial times has reduced the ocean’s pH by 30%, creating grave concerns for marine life across the board, much of which rely on pH stability for their acid-soluble carbonate shells and skeletons.

Another crucial reason small shifts in global temperature are cause for alarm relates to the dynamics of ice sheets and their built-in implications for sea level rise. An increase in average terrestrial temperature creates a shift in the boundary between ice and land. Indeed, the observed change of “just” 2 degrees Fahrenheit since 1880 has already yielded costly ramifications in terms of ice sheet integrity and global sea level rise. The unprecedented melting of the Greenland and Antarctic ice sheets, together with the thermal expansion of seawater, has raised sea level by a foot since the late 1800s.

The latest IPCC report projects another 1.6 ft (0.5 m)-3.2 ft (1 m) will come by the end of this century. Again, our intuition tends to balk at these numbers, to write them off as too small to warrant concern. Yet given that globally more than 150 million people live within that upper bound projection of sea level, this should be immediate cause for concern.

What’s more, these figures do not account for the possibility that tipping points are reached before we can scale back our emissions habit. A full-blown collapse of the West Antarctic ice sheet alone would add another 10-13 ft (3-4 m). If Greenland and Antarctic losses begin to accelerate, we could see more significant rises still. In total, the Greenland ice sheet contains between 20 ft and 23 ft (6 m) of sea level rise, while the elephantine Antarctic ice sheet, if melted in its entirety, would raise sea level anywhere from 200 ft (61 m) to 240 ft (73 m). At the planet’s current population size, economic dangers and civil conflicts would emerge long before we approached these figures.

Thus what sounds trivial according to our intuition is actually, empirically speaking, quite consequential. Extrapolating seemingly minuscule changes in phenomena like CO2 concentration, mean temperature, and sea level rise to a global scale produces a constellation of near- and longer term concerns with the potential to disrupt the kind of society to which we’ve been accustomed these last few hundred years. Especially if business as usual emissions continue unimpeded, droughts and wildfires, supercharged hurricanes, increased flooding, sabotaged food chains and the extinction of keystone species, and a stalled polar jet stream — all acute indicators of a hastily warming planet — will serve as enduring reminders of how far we have pushed climate parameters outside the range for which much of global civilization is adapted.

Intuition is overrated. We know the degree to which our planet has changed, we know the time scales associated with changes of the past and the present, and we know how the planet has responded to similar changes in the past. All else equal, movement of one-degree Celsius is something we should sit down and talk about, as is a foot of sea level rise. When those changes occur at a faster clip than can be reconciled to historical data, with more expected in the future, it’s time to act.

Honing Our Language

Switching to an entirely different discussion in the podcast, Romm says at one point that he avoids using certain terms like ‘theory’ and ‘consensus’, presumably in conversation with laypersons, because these terms have conventional meanings out of sync with their scientific meanings.

Regular readers of mine can probably guess how I feel about this, but here’s the thing — we shouldn’t apologize for using the language of science to communicate basic facts about reality. That far too much of our electorate is oblivious to the ways in which colloquial definitions in scientific parlance don’t always map to the formal definitions is largely a failure of our educational process and secondarily a product of decadeslong disinformation campaigns funded by the likes of Koch, Murdoch, ExxonMobil and Shell and propped up by denier blogs like Breitbart and WUWT (inter alia).

The approach here is not to cave to the rhetoric peddled by obfuscationists, but to educate and inform, clearly and diplomatically, to dispel common myths and misconceptions no matter how deeply embedded, and also (this is key) to help the public understand the methods and means employed by misinformation channels. Knowing how denialist groups intend to manipulate you — and the various ways in which we are susceptible — can serve as a heat shield against future falsity.

One caveat, however — there is certainly a limit to how much jargon we should work into conversations outside the academy. Dropping high-level technical terminology or Latin designations of species at every turn is ill-advised. The difficulty lies in balancing simplicity and clarity with scientific accuracy, which is why we should promote and support the journalists who get it right (there are many).

Listen to the episode below.

External link:  What You Need to Know About Climate Change: A Conversation with Joseph Romm

Further reading:  A Climate of Change

Feature image via InterfaceLIFT