The 3‐Machines Energy Transition Model: Exploring the Energy Frontiers for Restoring a Habitable Climate

Abstract

To stabilize the climate, we need to urgently decarbonize our society and remove excess CO2 from the atmosphere. Ambitions for the transformation are ultimately limited by bio‐physical constraints, which cannot be transgressed even if all economic and societal obstacles could be overcome. Even though it is essential to know what transformation pathways are still feasible, there is a lack of studies and models exploring bio‐physical frontiers for climate action. In this paper, we take a first step to explore the energy frontier by introducing the “3‐machines energy transition model.” This simplified representation of the global energy system includes energy feedbacks and is constrained by the maximum renewable energy potential. Simulation experiments with the model show that with most ambitious actions global peak heating may exceed 1.5°C with a chance of 14%. Simultaneously, it is still energetically possible to return to 350 ppm this century, which is considered to be a safe level for atmospheric CO2 concentration. While these energy‐constrained transformation pathways show that the climate can still be stabilized with a fair chance, they also illustrate the urgency and far‐reaching change required in society.

Below zero

“…46 Afforestation can increase C in living biomass. Direct air capture (DAC) is limited by the sustainable potential of renewable energy 21 and by far the largest potential NET flux. C from DAC and BECCS can be transported and stored in geological storage or incorporated in products and cycled within the technosphere.…”

“…Capturing CO 2 directly from the ambient air is energy intensive, but in contrast to bio-based solutions nearly independent of land availability. 69 When powering direct air capture (DAC) with solar PV from the already built environment, 21 additional land conversion is negligible. 70 There are different DAC technologies available, some already at pilot scale and others in development.…”

“…18–20 Reaching 350 ppm—or any other long term climate target—inevitably requires below zero emissions at a massive scale. 21,22…”

“…In the beginning of the transition, it can only come from the fossil energy system. 9,21,30 A minimum of 50 Gt of C has to be emitted to achieve the energy transition. 9 When exhausting the remaining carbon budget for 1.5 °C with 50% confidence, this increases to 100 Gt of C (Fig.…”

“…[18][19][20] Reaching 350 ppm-or any other long term climate targetinevitably requires below zero emissions at a massive scale. 21,22 The current debate on climate action centres around reaching net zero emissions globally in about 2050. In this narrative, which can be summarized as "Do your best, remove the rest", 23 "hard-to-avoid" emissions can be continuously compensated by negative emissions.…”