This essay has prompted a viral response in the media and among scientists. You can see the article here  web link to the essay

Here Phil Williamson describes the key points and the response to date.

The Hothouse Earth scenario explored by Will Steffen and his co-authors others remains uncertain: it is not covered in most models of climate change.  But unfortunately that does not make uncontrolled warming implausible.  On the contrary, recent geology shows us that the Earth’s climate system is inherently nervy – with stability for more than a few centuries being the exception rather than the rule.  For the past million years or so the interplay of physical and biological processes has resulted in the cooling and warming of the ice age cycle, with sea level changes of around 100 m occurring several times over the period of human evolution.  That didn’t matter that much to us then; it does now – with human processes also part of the mix.  As a result of human impacts on climate, the new paper argues that we’ve gone beyond any chance of the Earth cooling ‘of its own accord’.  Instead, there is the opposite risk, involving a vicious circle of positive feedbacks, each accentuating warming.  For example, by permafrost thawing, forest dieback and the biological release of carbon from the soil and ocean.  Together these effects could add an extra half a degree Celsius by the end of the century to the warming that we are directly responsible for ‒ thereby crossing thresholds and tipping points that seem likely to occur around 2⁰C, and committing the planet to irreversible further change, as Hothouse Earth.   There is still some scope for optimism, in that there is international agreement (with one rather important exception) to take action to avoid such consequences.  Steffen and his colleagues argue that we need to be much more proactive in that regard, not just ending greenhouse gas emissions as rapidly as possible, but also building resilience in the context of complex Earth system processes that we might not fully understand until it is too late.  In the context of the summer of 2018, this is definitely not a case of crying wolf, raising a false alarm:  the wolves are now in sight.”

Phil Williamson School of Environmental Sciences, University of East Anglia, Norwich NR4 7TJ, UK

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13/8/18 Further comment: Phil Williamson – ‘this was as online via the Science Media Centre, with a couple of other comments (at on the original paper.

Additional scientific discussion has included a Conversation article by Richard Betts (MetOffice/Exeter) at  Whilst there’s not that much difference between us, meteorologists (and modellers) do tend to be more cautious, taking the view that the climate is inherently stable.  I’m not so sure; the geological record would seem to indicate otherwise – and just because feedback effects aren’t in the models doesn’t mean they can’t happen. Online media coverage of original article with my quote now ~520; I came across foreign language coverage over the weekend that I had missed before.’

Greenpeace comments: A new study is exploring, portraying a widely-publicised future called ‘hothouse Earth.’ What’s ‘hothouse Earth’? Well, the study warned that a series of cascading events could move Earth into a state beyond which there was no return. Essentially, the study warned that even limiting global warming to 2C might not be enough for stable future temperatures. However, the suggestion that there was a point at which events were no longer avoidable was criticised by other scientists, including Professor Simon Lewis, who once featured in a video for us, and those who broke down the nuance in the science.

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