How bifurcation theory explains the stakes of the climate crisis

Photo by David Barajas on Unsplash

Humanity’s climate choice

The human species is at a critical juncture in its history. During less than a century it managed to burn hundreds of gigatons of fossilized biomass. Since the beginning of the industrial revolution, more than 1.5 trillion tons of CO2 molecules that were sequestered millions of years ago have been released into the atmosphere, enough to push the Earth’s natural carbon cycle well out of its natural state of balance. As a result, the atmospheric CO2 concentration began to rise at an unprecedented pace (we are currently approaching 420 ppm), increasing the strength of the greenhouse gas effect and pushing the Earth’s solar energy balance out of its equilibrium, too. Consequently, an increasing amount of excess heat energy is accumulating within the Earth’s climate system, overheating acidifying oceans, amplifying extreme weather events, and distorting the polar jet streams. Rising mean global temperatures are driving biodiversity losses and ecosystem decline at an unprecedented scale. This is the ecological debt which the human species has incurred as the price for much of the economic wealth created since the end of the second world war — first unknowingly, but now inexcusably. Even more perilous is the geopolitical chaos to be expected during this century, induced by decline of fresh water reserves and agricultural productoin capacity, rising sea levels and forced migration. These developments will further destabilize human societies and escalate conflicts over critical resources with the possibility of nuclear wars, thereby jeopardizing the potential for future human progress altogether. But it doesn’t have to be this way. With enough determination, visionary leadership and collective resolve, mankind could still stabilize the climate before it’s too late — the technologies needed to begin with largely exist.

The highway metaphor

Imagine you are driving on a busy highway, with your family on the backseat. You need to take an exit ramp in order to arrive at your destination, but you have already missed the first few exits. Each missed opportunity is extending your travel time disproportionately: Rather than driving towards your destination, you are actually driving away from it by now. You are becoming aware that you are getting dangerously close to the last possible exit before running out of gas. Missing it would force you and our family to abandon your vehicle for a long and perilous journey by foot. The closer you get to this point of no return, without having taken the right lane and having sufficiently slowed down, the more unlikely, difficult and dangerous the last possible saving maneuver becomes. In the absence of a navigation system, we cannot know for sure how how many more exists we may miss — all we know is that there really aren’t many left. The margin of tolerable error is ambiguous but narrow. Yet our continued reliance on fossil fuels is the equivalent to a reckless and delusional driver, who is keeping his or her foot firmly on the gas pedal and the steering wheel locked. The climate choice human civilization is currently faced with is similar to the situation just described. Indeed, the climate emergency does not represent a normal challenge with a continuous spectrum of outcomes but confronts us with an either-or choice. UN Secretary General Antonio Guterres recently made a remarkable statement in this regard when he explained: “We have a choice. Collective action or collective suicide. It is in our hands.”

The bifurcation threshold

The reason for this either-or characteristic is the possibility of a bifurcation at a planetary system scale — a planetary tipping. A bifurcation describes a relatively sudden qualitative change of a dynamical system due to a change of a critical parameter. In its simplest form, a system at a stable equilibrium, which is subjected to an external forcing (i.e. a perturbation ) that pushes it across a tipping point threshold (the “bifurcation threshold”), reaches an unstable state, during which it “tips” and swiftly and autonomously re-adjusts towards a new, substantially different state of balance. One can think of a pond that has been infected by algae — as the biomass growths gradually but exponentially over the course of days, the pond’s ecological carrying capacity eventually becomes overwhelmed. The pond tips and it’s carrying capacity rapidly declines, the ecosystem collapses within a matter of hours. In general, getting a system to tip requires orders of magnitude less effort than reversing an on-going or already occured tipping dynamic. With regard to the earth’s climate system, such a bifurcation is driven by the level of atmospheric CO2 concentrations. In addition, the earth’s climate system is characterized by cascading tipping points, positive geological feedback loops that become activated at certain temperature thresholds and are likely to trigger a geological hothouse earth dynamic over many millennia. This means that the human response to the climate emergency comes down to a either-or choice: Either we manage to restore the climatic conditions of the Holocene in time, before triggering a hothouse Earth dynamic on the way, or we will have to endure it. Each choice is characterized by very different post-bifurcation solution sets:

A) The “Hothouse Earth” pathway: Maintaining the delusion of continued economic/social prosperity and reliance on fossil fuels through business-as-usual for several more years comes at the incalculable cost of collapsing ecosystems and ecological carrying capacity, social instability, and an increased risk of failed states and resource wars on a planet that would be ruined for the human species for millions of years to come.

or

B) The “Restored Holocene” pathway: By making an extraordinary effort during the 21st century (and beyond), supported by a combination of bold climate policies (including sufficiently transformative carbon pricing, strong fossil fuel replacement and phaseout mandates and vastly increased public spending), we manage to stabilize climate conditions and presere the possibility of continued human progress for generations to come.

A schematic illustration of the two post-bifurcation pathways and possible outome ranges/solution spaces is shown below.

The possibility of restoring Holocene-like climate conditions

As long as there is a possibility to reduce atmospheric CO2 concentrations at a sufficient pace and scale, a bifurcation of the Earth system can be prevented, stopped, or slowed down. Indeed, restoring and preserving the climate conditions of the Holocene as much as possible represents humanity’s most consequential, decisive mission for the next century, perhaps even centuries. This requires first reaching net zero emissions, followed by substantial net negative carbon emissions within the 2nd half of the 21st century and beyond. The IPCC’s special report “global warming of 1.5 C” describes a range of scenarios (the “interquartile range” for no or limited overshoot) in which — depending on the near-term GHG emissions pathway — between 550 to 1,017 Gigatons of CO2 molecules will need to be permanently removed from the atmosphere. This is an extraordinary technical and economic challenge which requires the mobilization of immense resources in terms of raw materials, land and energy. A staggering volume of GHG emissions released in the past, present and future will need to be filtered and permanently removed, at an economic and societal cost that by far exceeds their massively subsidized short-lived economic gains. To put these numbers into perspective, human civilization is currently emitting ~50 Gigatons of CO2 p.a. into the atmosphere, while the global carbon capture and storage (CCS) volume currently only amounts to 0,04 Gigatons p.a. Fortunately, a bio-bsaed removal technology is already commercially available. By substituting cement by engineered timber, buildings can be turned from a carbon source into a carbon sink, utilizing sustainable forestry as a gigantic biological carbon pump.

Two critical conditions for success

Provided that fossil fuel-based emissions can be rapidly forced down by mid-century, it is conceivable that negative carbon technologies can be deployed at sufficient scale to let the atmospheric CO2 concentration first peak and then decline to “safe” levels (~i.e. less than 350 ppm). But for this civilizational moonshot enterprise to possibly succeed, at least two critical conditions must be met:

• Cascading tipping points of the Earth system must not have become an overwhelming counter-force by the time net-negative anthropogenic GHG emissions have been achieved. There is a risk that already triggered tipping point dynamics cannot be deactivated any more and release additional greenhouse gases at a faster pace than they can be reduced and removed. This uncertainty can only be managed by slowing down the pace at which the atmospheric CO2 concentration continues to rise as much as humanly possible. Note that by the time we can be absolutely accurate certain about the exact timing and resources needed to restore pre-industrial atmospheric CO2 concentrations, it will be too late.
• The capacity for a transition to a negative carbon economy under peaceful conditions must be maintained. The great challenge is that until global GHG emissions become net-negative , rising temperatures and collapsing ecosystems will have put human civilization under an increasing pressure. Global heating and induced geopolitical tensions must be sufficiently managed and mitigated to maintain the minimal conditions for effective international cooperation and technology and resource deployments. Since resources are limited (especially when a large share is wasted on the buildup of military capacity and nuclear weaponry) at some point it will likely become impossible to spend sufficient resources on preventing planetary tipping, while keeping societies stable against an increasing pressure to spend resources on adaptation and militarization. Of course, without meeting an increasing demand for absolutely necessary adaptation, mitigation would no longer be possible. But it is important to realize that without sufficient mitigation, any adaptation would be unsustainable and in vain, since unmitigated natural and social forces would eventually overwhelm human adaptation capacities. At the current state, even an irrecoverable collapse of human civilization cannot be ruled out (a risk that tragically tends to be overlooked by influential proponents from the effective altruism movement).

Missing the last safe exit

But even if humanity missed the “last safe exit”, and ultimately failed to prevent the bifurcation of the Earth’s climate system, this generation (we) would not be off the hook that easily. We would still be ethically obligated to do everything in our power to limit the cumulative climate damages and losses and maintain the possibility of future recovery and human progess. We would still have an inescapable responsibility to slow down the Hothouse Earth dynamic as much as possible, in order to buy young and future generations precious time to adapt to and stabilize, even at a lower level of civilizational and ecological complexity. It can still get worse, and it can still get better. Coming back to the highway metaphor: even though we may realize that we are unable to reach our destination by car any more, we would still at least have to try to get as close as possible to our destination and make sure as much as possible that we eventually strand on walkable, less perilous terrain. This would still be much more preferable than the undesirable scenario anticipated by the philosopher Slavoj Zizek, the equivalent of human civilization barely surviving, ending up lost and disoriented in the middle of a busy highway: “the last exit before the final one will be some version of what was once called “war communism.”, […] a warlike emergency state […] to simply guarantee the minimal conditions of our survival…”.

The race against time

It is important to recognize that the possibility to prevent the Earth-system level bifurcation (planetary tipping) is only a temporary one, constrained by a closing window which has been wide open (and unforgivably ignored) for more than 30 years. This is why humanity finds itself now in an increasingly difficult and perilous race against time. With regard to the window to prevent too many cascading climate tipping points from activating, it is uncertain when exactly this window will be closed for good — but it is rather certain that stabilizing significantly below two degrees C represents an absolute minimum condition to keep it open. A second window to maintain the capacity for transitioning ro a negative carbon economy under peaceful conditions is even more speculative — it might remain open for some years or decades, depending on the wisdom and resilience of our societies, the strength of political will, ethical reason and scientific rationality. The “doomsday clock” by the Bulletin of the Atomic Scientists” offers a rough indication and currently stands at 100 seconds to midnight. Nevertheless, with extraordinary effort and international collaboration there is still a chance that the pace at which negative-emission technologies are deployed beats the pace of tipping point dynamics, geopolitical risks and social destabilization. This possibility, unlikely as it may seem, is supported by the existence of positive social tipping point dynamics with the potential to accelerate our civilization‘s’ transformation for the better. Rutger Bregman’s groundbreaking reassessment of human nature as being evolutionary hardwired by instincts of kindness, collaboration and social learning, offers hope that as the crisis deepens, human compassion and solidarity can be harnessed as a positive force for change.