A new perspective piece published in PNAS proposes novel processes through which the planet could enter a ‘Hothouse Earth’ state. The mechanism, the climatic equivalent of a gravitational slingshot, could propel us toward extreme climate change quicker than previously thought – which was already “pretty fast”, remarked one source. Yet, whilst US governmental agencies preoccupy themselves with climate deregulation, a point of no return approaches, totally unphased and mostly unnoticed. But what are the climate change tipping points and cascades in the Earth system?
A tip of the hat
Lenton et al. first coined the term ‘tipping element’ in 2008, setting the stage for research into climate tipping points. The term describes the large-scale biophysical features of the Earth’s climate such as Arctic sea ice and the Amazon rainforest. All these features would be significantly altered after surpassing as-yet unknown climate thresholds. The nature of these tipping elements makes it extremely difficult for them to return to their original states.
Bite the hand that feeds
The new report by Steffen et al. suggests that 2°C of global warming could trigger a tipping cascade. The report uniquely considers self-reinforcing feedback loops such as the effects of tipping elements on one another, and how this could impact human control over the future climate. Such runaway feedbacks could lead to a ‘Hothouse Earth’ faster than current models predict. We are already ~1°C above pre-industrial levels and as temperature increases lag emissions, humanity may already be committed to a pretty sketchy game of chicken.
2 little too late?
The Paris Agreement aims to limit global warming to 1.5 – 2°C based on findings from the IPCC report. Not everybody agrees on the finality of those 2 degrees of warming. Most scientists, such as Anders Svensson, feel the climate system is too unpredictable to assign a safe level of warming – it could be more, but it could also be much less.
Climate policy does not yet consider nonlinear mechanisms such as tipping cascades presuming that mitigation actions can restore previous conditions. Steffan et al. propose this is as an oversight requiring renewed levels of stewardship in response.
– Andrew Hattle, Janani Venkatesh, Jesse Jones