After Overshoot: Can Life Prevail?
Global warming is already locked in, with further temperature rises inevitable. This article explores the warming in the pipeline, the cascading tipping points, and what that means for the planet.
In this article I’ll explore a few studies on the long-term impacts of climate change and what this means for the planet and our overshoot predicament.
But first, I still get the occasional comment that climate change is a hoax, or that more CO₂ is great for life, so let’s set the record straight.
(1) The problem isn’t high CO₂ itself, but how quickly it changes. Greenhouse gases trap heat in the atmosphere, acting like a thermostat, which drives rapid warming and ocean acidification. This triggers feedbacks that further accelerate warming as the Earth shifts toward a new equilibrium. When CO₂ levels and temperatures rise gradually over thousands of years, ecosystems, flora and fauna can migrate and adapt, because the overall conditions they evolved in are still largely the same. No major issue.
But a sudden increase or decrease in CO₂, and ecosystems can’t keep up.
High CO₂? Not a problem. Rapidly changing CO₂? Disaster.
Bottomline: Any abrupt shift in the conditions that plants and animals have adapted to over millions of years will be catastrophic. There is zero evidence to support that they can adapt to rapid changes. Show me the evidence of when life thrived during a rapid increase of CO₂? It doesn’t exist.
(2) All mass extinction events share a common thread: a rapid environmental change that outpaces the ability of species to adapt. Many of these events were triggered by massive volcanic eruptions that released CO₂ and other gases into the atmosphere.
These eruptions often caused an initial cooling phase due to sulfur dioxide (SO₂), which reflected sunlight and cooled the planet for months or years. But what followed was a prolonged warming period lasting millennia. This warming destabilized ecosystems and food chains. This was the kill-mechanism.
Bottomline: Rapid release of CO₂ has always led to mass extinctions, the evidence is clear. This will no exception. It’s all about (A) the pace of change, and (B) how well the Earth’s systems, like the oceans, forests, soil, and the carbon cycle, can buffer these shifts by sequestering CO₂.
(3) Right now, we’re cranking up the thermostat by releasing CO₂ at the fastest rate in at least 66 million years. Yes, it’s us. And yes, this is likely the fastest rate ever, but we can’t definitively prove it.
And how are the Earth’s systems doing? As far as we know, the Earth’s ecosystems have never been in such a degraded state at the onset of a mass extinction event. Here’s a chart from a 2021 study that illustrates the scale of our environmental destruction:
Bottomline: This is a complete disaster, and no amount of green energy will fix it. If anything, it would make things worse because it allows us to keep doing what we’ve been doing: destroying the planet under the illusion that we’re “saving” it. Having said that, it’s still vastly better than burning fossil fuels at current rates.
So, let’s look at what we’re facing in the coming decades and centuries, but first a quick recap of climate history.
Leaving the Holocene
Our entire way of life is rooted in agriculture, a practice that began just 10,000 years ago, thanks to the stability of the Holocene. As far as we know, agriculture only works in these stable climate conditions. Without that stability, it simply doesn’t work. It’s also crucial to understand that our cities and infrastructure were built for conditions (temperatures, precipitation, sea-level) that are already in the rear-view mirror.
Temperature range: 0.5–1°C
Atmospheric CO₂ range: 20 ppm
Civilization is a 5,000-year experiment and it’s already failed repeatedly. It hasn’t had to survive glacial cycles or extreme climate shifts, instead, it has collapsed every time under the most stable conditions Earth has ever provided. Civilizations collapse for many reasons, but at their core, they are inherently unsustainable, inevitably depleting resources and exceeding the carrying capacity of their environment.
Modernity, the version of civilization we live in now, has barely been around for a couple of centuries and managed to wreck and pollute the planet beyond recognition.
But we’re not only leaving the Holocene behind us.
Leaving the Quaternary
For 2.6 million years, we’ve been in the Quaternary period, during which Earth's climate has fluctuated within a somewhat predictable range between glacial and inter-glacial periods. These fluctuations were driven by orbital forces called Milankovitch cycles, which refer to changes in Earth’s orbit, tilt and wobble that affect how solar radiation (heat) reaches the planet.
Temperature range: 5–6°C
Atmospheric CO₂ range: 120 ppm
These cycles, repeating roughly every 100,000 years, did not trigger any major extinction events, as forests, plants, and most animals had time to adapt and migrate at this natural pace.
We left the Quaternary behind decades ago when we surpassed 350 ppm, probably even earlier than that. Had we stopped at 350 ppm, radically changed our way of life, and kept our population in check, perhaps we could have avoided this disaster and experienced a more gradual collapse instead, retreating back to simpler lifestyles over a few centuries or millennia, similar to the decline of the Roman Empire.
I wish that were still possible. But it’s not.
IPCC, Tipping Points, and Warming in the pipeline
First of all, you can forget the RCP scenarios, which we are often shown, because they do not factor in all tipping points or feedbacks.
Not included:
Permafrost thaw and methane release
Amazon rainforest dieback
Antarctic and Greenland ice sheet collapse
AMOC slowdown
Meaning, they are not at all realistic.
This is why we constantly see those faster than expected headlines. But even with just 2°C of warming from human GHG emissions, tipping systems could push us onto the RCP8.5 path, driving temperatures to 5.4°C by 2100 through feedback loops.
Trajectories of the Earth System - Steffen et al. 2018
In this 2018 study, Will Steffen, Johan Rockström and other researchers examined potential pathways for the Earth System, focusing on when we might reach a tipping point that could destabilize the entire system and push us toward a “Hothouse Earth”.
They identify the following tipping points, or feedbacks (below). The color shows the temperature at which they are likely to tip, and the arrows show how they interact, potentially leading to tipping cascades.
I will get back to these later when we review the current state of things and how a tipping cascade can unfold.
Key takeaways:
They conclude that warming of 2°C is the limit, beyond that, we lose control of the situation and could see a tipping cascade
They argue that the only way to avoid catastrophe after crossing 2°C of warming is through human intervention (massive carbon sequestration)
Global warming in the pipeline - Hansen et al. 2023
This study is even more alarming than the last. The authors analyzed climate sensitivity, our climate system’s delayed responses (inertia) and amplifying feedbacks, and reached some chilling conclusions: we already have 8-10°C of warming in the pipeline, even if we stopped emissions today. What?! It's the feedbacks. These can be broken down into three categories:
Slow feedbacks: Tipping points like ice sheet changes (albedo), ocean currents, and vegetation shifts
Fast feedbacks: Water vapor, cloud formation, and sea ice loss
Ultra-fast feedbacks: Earth's energy imbalance, stratospheric warming and cooling
This is more than just about how much CO₂ we emit and how that might raise temperatures in a simplistic, linear model (AOGCM). It’s about how that heat is absorbed by the atmosphere, oceans, and land, and how it triggers feedbacks over decades, centuries, and millennia, ultimately driving even more warming and more emissions.
What to expect according to the study:
The role of Sulfur Dioxide - Aerosol Masking
Remember how mass extinction events from volcanic activity often have an initial cooling phase? The study proved that we’ve essentially been replicating a massive volcanic eruption, especially in terms of sulfur dioxide (SO₂).
Over the past century, we've released 3-5 times more SO₂ into the atmosphere than normal volcanic activity, which has been masking the heat and causing an initial cooling period (yes, this was the cooling phase). But as we cut SO₂ emissions from industries and shipping, that cooling effect is fading, and we’re heading into a dangerous phase where things are about to spiral out of control.
Key takeaways from the paper are the following:
Accelerated warming is inevitable, with 2°C of warming guaranteed by 2040, based on Earth’s Energy Imbalance (personally, I think we’ll breach 2°C as soon as 2032, possibly with the next El Niño).
We are already committed to 8-10°C of warming if no action is taken.
This warming is driven by feedbacks
Human-made aerosols are currently masking about 1.5-2°C of warming
They also conclude that the only way to avoid this warming is through human intervention (massive carbon sequestration)
If that all sounds a bit confusing, you can watch this video where James Hansen and other authors walk through the key findings. It’s highly technical, but worth diving into.
Feedbacks – The Power of Ice
The big fear about ice sheets is not sea-level rise, it’s the huge amplifying effects of a runaway albedo-ice feedback.
The terms Hothouse Earth and Icehouse Earth refer to two contrasting states of Earth’s climate:
A Hothouse Earth is a hot, ice-free planet with extreme warmth and high sea levels. In this state, the Earth experiences little to no polar ice, and temperatures are much higher than today.
An Icehouse Earth is a cooler planet characterized by large ice sheets and glaciation, with significant ice coverage at the poles. During this state, Earth’s temperatures are much lower, and ice plays a major role in regulating the climate.
The main difference? Whether or not ice exists.
We are currently in an icehouse state, and have been for millions of years. How did we get here?
Long story short, around 34 million years ago, the opening of the Drake Passage, led to the formation of the Antarctic Circumpolar Current (ACC). This current, which now encircles Antarctica, isolated the continent, allowing it to cool, triggering the growth of ice sheets.
This marked the official start of our current Icehouse Earth and the beginning of permanent ice sheets.
Several slow feedback mechanisms followed, amplifying the cooling:
Increased albedo: The lighter ice surfaces reflected more sunlight, reducing heat absorption and cooling the planet further.
Cooler oceans: Cooler oceans helped lower atmospheric CO₂ levels by promoting the burial of organic carbon on the ocean floor.
Drier, cooler atmosphere: As the climate cooled, tropical and subtropical forests were replaced by dry woodlands and expansive grassy areas, further increasing albedo and reducing atmospheric moisture.
On the opposite side of the planet, the Arctic didn’t become permanently covered in ice until about 2.6 to 3 million years ago. While it wasn’t as dramatic as Antarctica, the closure of the Isthmus of Panama around 3 million years ago played a major role.
When the Isthmus of Panama closed, it altered ocean currents, particularly strengthening the Gulf Stream. This shift in circulation led to increased evaporation and snowfall in the Arctic, helping to trigger its ice buildup.
Why is this relevant? The polar ice caps and ice sheets are melting at an unprecedented rate, and this rapid loss of ice could single-handedly push Earth’s systems past a critical tipping point.
When The Dominoes Fall – Tipping Cascades
Let’s take a closer look at those tipping points and how a tipping cascade will likely unfold in the coming decades, based on Will Steffen’s 2022 video presentation.
The Arctic sea ice is already mostly gone, drastically reducing the Earth’s albedo and increasing temperatures in the Arctic. This tipping point has essentially been crossed. The Arctic is now warming far faster than other regions, as shown in the graph below.
This accelerated warming drives the melting of the Greenland ice sheet, further reducing albedo and releasing massive amounts of freshwater into the Atlantic. This influx of fresh water slows down the Atlantic Meridional Overturning Circulation (AMOC), which regulates global climate.
At the same time, reduced albedo and rising temperatures are thawing permafrost, releasing previously trapped greenhouse gases (methane and CO₂). This creates another amplifying feedback loop that further intensifies global warming. The warming also increases methane emissions from wetlands worldwide, compounding the problem.
A severely weakened AMOC will have cascading effects.
It will reduce rainfall over the Amazon by roughly 50%, making the region much drier and more prone to fires. This will lead to the Amazon rainforest transitioning into a savanna, releasing enormous amounts of CO₂ into the atmosphere and further driving warming.
In Europe, it will lead to more extreme weather, harsher winters, and reduced rainfall.
In North America, it will cause more intense storms, disrupted weather patterns, shifts in agricultural zones, and sudden sea-level rise along the eastern coast.
Additionally, a severely weakened AMOC will accelerate ice loss in the West Antarctic ice sheet and the Wilkes Basin by redistributing heat to the Southern Hemisphere, altering ocean circulation, and shifting atmospheric patterns.
These interconnected tipping points are not distant, they could all unfold before 2045.
It’s already in motion.
The Arctic could be ice free by summer 2027
Scientists warn of collapse of the Atlantic meridional overturning circulation AMOC
For the 28th year in a row, Greenland's ice sheet is shrinking
Unavoidable future increase in West Antarctic ice-shelf melting
Looking Ahead – Anthropocene 2100-2300
Wherever we’re headed, it’ll start with a bang. What comes next is anyone’s guess.
We’ve already cranked up the CO₂ thermostat to 426 ppm as of this writing (closer to 500 if you factor in other greenhouse gases i.e. CO₂e), and the Earth’s energy imbalance is locked in to push temperatures up, way faster than nature can adjust.
As Earth’s systems spiral into chaos, global industrial civilization faces inevitable collapse from a convergence of crises, as outlined in these articles:
This means there will likely be no large-scale, coordinated human intervention to prevent catastrophic outcomes triggered by climate tipping points. An effort both studies identify as crucial.
Even if civilization collapses soon or emissions are drastically reduced voluntarily, atmospheric GHG levels will still reach the equivalent of around 550 ppm by 2040, and would keep rising from human emissions for a long time.
Why?
We are Fire Apes and our fundamental problem is overshoot. Think about it. As long as modern humans exist in vast numbers, emissions will keep rising. Because long before fossil fuels, we burned biomass for cooking, heating, and survival, and we’ll keep doing so, collapse or not. Fire has been central to agriculture too, from clearing land for crops to managing grazing areas. Even with a reduced population, say 3 billion people by 2050, burning just 3 kg of biomass per person daily adds up to 6 billion tons of CO₂ annually.
Here are a few articles indicating this will likely be the case:
Whatever happens, we will see global temperature rise of 3–5.4°C by century’s end, probably sooner.
As we pass through tipping points, the thermostat will keep rising. Projections like those from Hansen et al. suggest we could ultimately see 12–14°C of warming, though that may take centuries or millennia.
While the oceans will absorb some CO₂ over the coming centuries, making them even more acidic, much of it will remain in the atmosphere for thousands of years. The oceans will eventually release stored CO₂ back into the atmosphere, amplifying the warming.
With much of Earth’s carbon sinks destroyed and ecosystems crippled, the natural processes needed to draw down CO₂ have been impaired. As a result, it will take an unfathomably long time, tens of thousands of years or more, for CO₂ levels to meaningfully decline.
We will likely face a scorched planet long before it can begin to recover, and even then, it will do so in a completely different climate. The planet will remain unbearably hot for thousands of years, with the journey to that future defined by catastrophic destruction.
To sum up, the emissions we've already released guarantee massive disruptions to Earth's systems, no matter what path we choose. Large-scale CO₂ sequestration, whether through natural methods (afforestation, reforestation, soil restoration) or engineered solutions (CCS, BECCS, DAC), will not be enough to stop this, as outlined here.
Whether we collapse by 2040
Whether we aggressively cut emissions by 2050, or any other arbitrary date
It likely won't change the long-term outcome much. However, the pace of change does matter. Reaching a tipping point is dangerous. Racing past it is catastrophic.
That’s why, despite this hopeless situation, it’s still worth fighting to preserve nature. Every fraction of a degree, every patch of unspoiled wilderness, every spared species, it all matters in the fight against environmental collapse.
At the same time, social tipping points, critical moments when collective human behavior shifts dramatically, could become an opportunity. While it’s hard to predict exactly what that might look like or what the impact could be, we’re likely to witness extreme changes in our societies. Maybe we end up with something great, like an eco-conscious, egalitarian society. Or maybe it’s a total disaster, like Nazi Germany on steroids, with authoritarian regimes and violence everywhere. Throw in the risk of nuclear war, and it’s clear these tipping points could save some of us or finish us all off fast.
Can this civilization prevail? Not a chance.
Can a global agriculture-based civilization prevail? No, not for a long time.
Can humans prevail? Maybe, but not many.
Can life prevail? Sure, some life will persist and eventually recover.
As I mentioned in my previous post, there's little we as individuals can directly control. But we do control how we spend our time and what we choose to do with it.
Make it count, and always be mindful of its impact on nature.
I’m especially tickled by how cloud formation itself may cease around 1200ppm, plunging us into Hothouse Earth pronto, with an additional +8C warming. This should make short work of any surviving stragglers. (Gallow’s humour)
Amazing. Super well written and concise. Thanks again for your time an effort.
8 degrees is shocking. We will probably all be dead by 5, so we catch watch the world burn from "the other side" I suppose.