Planet at risk of heading towards “Hothouse Earth” state

if “Hothouse Earth” becomes the reality,” warns co-author Johan Rockström, former executive director of the Stockholm Resilience Centre and incoming co-director of the Potsdam Institute for Climate Impact Research.

Hans Joachim Schellnhuber, Director of the Potsdam Institute for Climate Impact Research, says, “We show how industrial-age greenhouse gas emissions force our climate, and ultimately the Earth system, out of balance. In particular, we address tipping elements in the planetary machinery that might, once a certain stress level has been passed, one by one change fundamentally, rapidly, and perhaps irreversibly. This cascade of events may tip the entire Earth system into a new mode of operation.”

“What we do not know yet is whether the climate system can be safely ‘parked’ near 2°C above preindustrial levels, as the Paris Agreement envisages. Or if it will, once pushed so far, slip down the slope towards a hothouse planet. Research must assess this risk as soon as possible.”

Global map of potential tipping cascades. The individual tipping elements are color-coded according to estimated thresholds in global average surface temperature (tipping points; 18,43). Arrows show the potential interactions among the tipping elements, based on expert elicitation, which could generate cascades. Note that although the risk for tipping (loss of) the East Antarctic Ice Sheet is proposed at >5 degrees Celsius, some marine-based sectors in East Antarctica may be vulnerable at lower temperatures.

Cutting greenhouse gases is not enough

Maximizing the chances of avoiding a “Hothouse Earth” requires not only reduction of carbon dioxide and other greenhouse gas emissions but also enhancement and/or creation of new biological carbon stores, for example, through improved forest, agricultural and soil management; biodiversity conservation; and technologies that remove carbon dioxide from the atmosphere and store it underground, the paper says.

Critically, the study emphasizes that these measures must be underpinned by fundamental societal changes that are required to maintain a “Stabilized Earth” where temperatures are ~2°C warmer that the pre-industrial.

“Climate and other global changes show us that we humans are impacting the Earth system at the global level. This means that we as a global community can also manage our relationship with the system to influence future planetary conditions. This study identifies some of the levers that can be used to do so,” concludes co-author, Katherine Richardson from Center for Macroecology, Evolution and Climate at the University of Copenhagen.

— Read more in Will Steffen et al., “Trajectories of the Earth System in the Anthropocene,” PNAS (2018) (DOI: 10.1073/pnas.1810141115)