Extinction Events, Past and Future

I've been doing a bit of reading lately which is sadly applicable to our lives today in this, the year of our Lord Pedro Pascal 2023. Mostly stuff about climate change, naturally, but one book in particular comes about it a little sideways and plenty scary, particularly after the release of the latest IPCC report and the numerous recent studies about ocean circulation and ice melt.

Peter D. Ward's 2005 book, Under a Green Sky, is about climate change by way of prehistoric extinction events. Ward's thesis is one of scientific consensus: that all but the K-T extinction (the one with the meteor) were caused by climate change, to put it simply. And this is nothing new. We've known climate change was the driver of extinction for actual decades at this point (if the book's publication date didn't make it clear). But what we think of as climate change today and what led to the climate-driven extinctions of millions of years ago are two different things. To put Ward's thesis a little less simply, climate change–usually caused by CO2 released via volcanic action–leads to a change in ocean circulation, which causes parts of the oceans to die and give rise to what someone has probably called zombie bacteria, which use sulfur instead of oxygen to survive. If this sounds familiar to you, it should; it's my nightmare scenario. If this doesn't make any sense to you yet, don't worry, it will. Well, worry, but not about a lack of understanding.

Canfield Oceans and The Uninhabitable Earth

You may remember David Wallace-Wells' article from 2017, which was probably one of the loudest clarion calls for climate action since Al Gore's movie. In it, Wallace-Wells goes over a number of the ways in which our lives could become a horror show due to climate change. Wallace-Wells actually spoke to Ward for this article–he even touches on ocean acidification and anoxia as part of the trouble. But here's the thing: all the other ways that life becomes hard for us under climate change–the wildfires and rising tides and diseases and famines–are not the extinction event, as per Ward. The extinction event we are bringing on by releasing millions of tons of CO2 into the atmosphere is only beginning to get moving, as hinted in my IPCC letter.

You might say, "but wait, a million species are under threat of extinction!" And you'd be right. And it is absolutely a shame, and one that hurts to think about. But with at least 8.7 million species on the planet (and perhaps many more), these are rookie numbers. What's going to put this extinction event on the map is what comes after we really get the ball rolling. To put this another way, think of our extinction event as a cartoon trail of gunpowder leading to a cartoon bomb. The severity of the event today is just the path of destruction the burning gunpowder has traced so far, not the bomb. The bomb has yet to go off.

That metaphorical cartoon bomb is the Canfield Ocean, and it is effectively a mechanism for turning the Earth into an alien world. But let's back up again, real quick. All the world's oceans are tied together by what's sometimes called the "great conveyor belt," which is an interconnected system of thermohaline circulating currents–currents based on heat and salt levels, which change the density of water, allowing for motion through the depths. This conveyor belt is so enormous that one complete cycle for any given molecule of water takes about a thousand years. And while it's slow and enormous, it is also absolutely vital to the world as it is today. The conveyor belt is responsible for the distribution of heat across bodies of water and land that otherwise would be far colder–like the UK and Western Europe.

The problem is that climate change messes with both the thermo and the haline part of the thermohaline current. In the Atlantic, for example, the Atlantic Meridional Overturning Circulation (AMOC, for my fans) is getting disrupted by climate change through the melting of the Greenland Ice Sheet, which dumps fresh water into the circulation, and an overall increase in heat across the ocean (among other things). This disruption causes AMOC to slow down, and it could eventually cause the circulation to stop. Now, along with heat and salt differentials, the circulation also helps drive oxygen throughout the ocean, and if the circulation stops, so too, does the supply of oxygen through the ocean. Almost every living thing in the ocean depends on oxygen, and without it begins the first part of the real extinction event.

We call oxygenless water anoxic, and waiting in the bottoms of the ocean are the aforementioned zombie bacteria, which thrive in anoxic waters. There are bacteria that produce methane in low-oxygen depths, a green bacteria that produces hydrogen sulfide, and a purple bacteria that feeds off it. When the oceans are sufficiently anoxic that those dead waters have spread to the shallows, the bacteria multiply. Methane produced by these bacteria contributes to global warming, which worsens conditions, and what life is left struggling in these deadly waters are then poisoned by hydrogen sulfide, which does plenty of damage on the surface but also rises into the atmosphere, destroying the ozone layer and baking vulnerable, oxygen-producing life in ultraviolet radiation, thus locking the cycle in place. The cartoon bomb of our human-generated extinction event has begun to explode.

The Sinking Threshold

Reading Green Sky was not paradigm-shifting for me until about halfway through the book, when something that Ward probably fairly sped past hit me. And this may not seem significant to anyone other than me, but: Ward's states that for an extinction event to get rolling, the significant thing that has to occur is a change in the ocean circulation. I was under the impression that circulation must be dramatically altered or stopped entirely in order for the cycle of anoxia to begin. But it turns out that an alteration is sufficient. That's worrying. It's widely suspected that climate change has already weakened AMOC, and if that's the case, it will only get weaker. The mechanisms that we've activated through climate change are not going to slow down or stop anytime soon–melting glaciers and ice sheets will not stop for quite some time. In fact, half the world's glaciers could potentially melt even if we hit our emission targets. The latest report that I have seen on this subject gave a very alarming projection: it's estimated that the Antarctic thermohaline circulation will slow down by 40% by 2050–not that far off, in oceanic terms. And the article linked above notes that the ocean circulation is one whole system, so that what slows the Antarctic slows the world's circulation.

I find words fail me when considering this subject. I had written this newsletter without knowing about the last report I linked above, assuming that these forces are coming further down the road, though far sooner than we hope. That report changes things. I will be in my mid-60s in 2050, likely as not still alive to see, for a decade or longer, things get even worse. And we have AMOC to consider as well, the flow of which is being altered by separate gouts of freshwater. My initial conclusion to this letter stated that we are not likely to see a graveyard of anoxic waters overtake an ocean in our lifetime, but that we needed to be very concerned. That's no longer my takeaway from the information available. We very well might see it happen. And the devastation that will bloom from this complex, strange, and relatively quiet sequence of events is simply total. There is no living through it. Not for us. Not for most living things today.

And still, since writing that last paragraph, I must now include this report about new estimated speeds of ice sheet retreat.

The Great Dying

Over 250 million years ago, it is theorized that a massive amount of volcanic activity–producing over 2 million square miles of lava in Siberia–released a truly enormous amount of carbon dioxide (and some methane). These greenhouse gases were anywhere from 25% higher than they are today to 2000% higher by the end of the event. It's difficult to be precise within these timeframes, but it's likely that climate change occurred more slowly than it is today, but ultimately that the changes were far greater–so much so that fully 90% of all species on the planet were killed. Over any significant timeframe it can be somewhat difficult to say how exactly these species were killed off, because eventually you compete with migration and evolution. But one thing most plants and animals on the planet cannot evolve out of is choking on hydrogen sulfide. The Permian extinction event produced enough CO2, warmed the planet so much, that it's almost certain the thermohaline current was slowed and halted, creating anoxic zones in the ocean that spread and allowed for the proliferation of green and purple bacteria. These bacteria then spewed poison, methane and hydrogen sulfide, worsening conditions until not only was the planet much hotter than before, but the air itself was lethal or damn near.

Imagine a planet so hot it's unlivable. A world that decades ago suffered immense fires, rising seas, floods, earth-scouring storms. A world that ceased to provide the sort of bounty of food we're used to, a world torn apart by conflicts over simple necessities like water. You arrive here only a few years too late to meet another person, the last of the scattered tribes of humans finally giving in to starvation long after any sense of a civilization that we recognize was burned away. The seas are not yet Peter D. Ward's oily purple. The sky is not yet green. But the sun burns your skin with a peculiar sharpness, and the air is fetid with poison.

This is the Second Great Dying. An extinction event brought on not by any natural mechanism, but by the open greed of a few thousand people, people who have known the ramifications of their actions for fifty years. What happens on this planet today and in the future is not the fault of the vast billions of people on it, but by a few who chose, at every turn, to enrich themselves and impoverish others. Even today, as the narrative bends to accommodate the inescapable facts of climate change, we are told it is our consumption that must be curbed, that our choices within this system are capable of effecting change when they never really were in the past. If we're to avoid the Second Great Dying, we have got to come together, put aside our differences, and face our common enemy. It's not just the people who perpetuate the lie–though they should be the first with whom we reckon–but the very idea that their lives are the ones worth living, that things are what people need instead of community. That what one has is never enough, and that the beauty that still, as yet, exists around us is not something to be admired but something to be taken.