By Elisa Jiménez Alonso
A new study published in Proceedings of the National Academy of Sciences (PNAS) shows that Earth could enter what the authors call ‘Hothouse Earth’ conditions where the average global climate could stabilise at 4-5°C above pre-industrial temperatures and sea levels could rise 10-60 m higher than today.
Mitigation alone won’t be enough for ‘Stabilized Earth’
The study, which has received wide-spread attention, also shows that keeping global warming within 1.5-2°C – a state the authors call ‘Stabilized Earth’ – may be a more daunting task than previously thought. It would not only require a significant reduction of greenhouse gas emissions but also enhancing or creating new carbon sinks, efforts to actively remove CO2 from the atmosphere, possibly solar radiation management, and adaptation to climate change impacts that are already happening and unavoidable.
“Human emissions of greenhouse gas are not the sole determinant of temperature on Earth. Our study suggests that human-induced global warming of 2°C may trigger other Earth system processes, often called ‘feedbacks’, that can drive further warming – even if we stop emitting greenhouse gases,” says lead author Will Steffen from the Australian National University and Stockholm Resilience Centre.
Health, economies, and political stability at risk
‘Hothouse Earth’ could potentially be uncontrollable and dangerous to most of Earth’s population, especially if the transition happens within only a century or two, which, following current pathways, wouldn’t be unlikely according to the scientists. This in turn would have fatal effects on health, economy, and political stability, but could also make portions of the planet uninhabitable for humans.
The study shows that agricultural production and water supplies are especially vulnerable to severe climate changes, leading to hot/dry or cool/wet extremes. These, obviously, would have severe impacts on society. The authors say “societal declines, collapses, migrations/resettlements, reorganizations, and cultural changes were often associated with severe regional droughts and with the global megadrought at 4.2–3.9 thousand years before present, all occurring within the relative stability of the narrow global Holocene temperature range of approximately ±1 °C.”
A growing need for building climate resilience
As highlighted in the study, even if a ‘Stabilized Earth’ state is achieved, Earth will be warmer than “at any other time in which fully modern humans have existed.” It would also still lead to the activation of some tipping elements and radical shifts in the ecosystems that support human life. The researchers state that current development strategies focused on economy efficiency will not be able to cope with these trends.
The emphasis now should clearly be on strategies that have the potential to transform human systems and make them climate resilient. Speaking in broad terms, the authors point out five characteristics climate resilience strategies should have:
- Maintenance of diversity, modularity, and redundancy;
- management of connectivity, openness, slow variables, and feedbacks;
- understanding social–ecological systems as complex adaptive systems, especially at the level of the Earth System as a whole;
- encouraging learning and experimentation; and
- broadening of participation and building of trust to promote polycentric governance systems.
Additionally, the authors of the study emphasise that their initial analysis would need to be underpinned by further research and Earth System analysis and modeling studies to address three critical questions:
- Is humanity at risk for pushing the system across a planetary threshold and irreversibly down a Hothouse Earth pathway?
- What other pathways might be possible in the complex stability landscape of the Earth System, and what risks might they entail?
- What planetary stewardship strategies are required to maintain the Earth System in a manageable Stabilized Earth state?
Steffen, W., Rockström, J., Richardson, K., Lenton, T.M., Folke, C., Liverman, D., Summerhayes, C.P., Barnosky, A.D, Cornell, S.E., Crucifix, M., Donges, J.F., Fetzer, I., Lade, S.J., Scheffer, M., Winkelmann, R., and Schellnhuber, H.J. (2018) Trajectories of the Earth System in the Anthropocene. Proceedings of the National Academy of Sciences (USA), DOI: 10.1073/pnas.1810141115