Hothouse Earth and Positive Feedbacks

The extreme example of positive feedback is the atomic bomb; it’s made of a material where a single free neutron can split a nucleus and release energy plus two or more new free neutrons; if, on average, more than 1 of these new free neutrons splits another nucleus there is a runaway reaction and an explosion. The result of splitting a nucleus splits even more nucleuses. 

Some results of global warming themselves cause more global warming; they are positive feedbacks. The ‘Hothouse Earth’ scenario  is that one or more of these positive feedbacks kick in via a tipping point and climate change becomes a catastrophe (even if we rapidly curb greenhouse gas emissions); in its most extreme form, Earth becomes like Venus with very few life-forms surviving. This might sound alarmist, but it is worth pointing out that we’re observing that at least 2 of these positive feedbacks (Ice Melt, Permafrost Thawing) are substantially stronger than all previous predictions. 

Possible positive feedback cycles in climate change include…

Ice Melt

As Wikipedia reports, ice reflects sunlight; when it melts it can reveal land or sea and these don’t reflect sunlight so well – instead they heat up. The earth gets warmer and (of course) more ice is likely to melt as a result. We are currently observing levels of ice melt that are 50 ahead of predictions. 

Permafrost thawing

As temperatures rise and the permafrost thaws, methane is released into the atmosphere; methane is a powerful greenhouse gas and temperatures rise further. The scale of permafrost thaw observed today is 70 years ahead of predictions. 

Air conditioning

As a child I was surprised to learn that leaving the door of the fridge open makes the room hotter, not colder. A similar effect happens with air conditioning; it cools the indoors but warms the outdoors a lot more. But as the planet gets hotter people are turning more and more to air conditioning to stay comfortable. This consumes more energy – the Guardian reports that air conditioning accounts for about 14% of all energy use now – and of course heats the planet further. The number of AC units is expected to more than triple worldwide by 2050. Air conditioning has a double cost – it consumes energy and uses refrigerants that are the fastest-growing source of greenhouse gas emissions worldwide.


Hot, dry weather dries out the vegetation and increases the risk of fires starting accidentally or getting out of control (when started deliberately). The drier vegetation also makes the fire bigger once they have started. Climate change make fires a bigger problem; but the same fires then turn around an increase global warming by releasing CO2 and methane (from permafrost they thaw) or covering ice with soot (and absorbing more sunlight). ScienceNews reports on recent fires through the Arctic and the links to climate change and as I write this the BBC web-site leads with a report on the fires in the Amazon basin; the planet’s lungs are on fire. 


Over the past 5 years or so, more countries have fallen to forms of populism; the USA, Brazil, Italy, the UK, Turkey, India and Hungary. The specifics vary in each country but two common threads are hostility to both migrants and policies that promote climate change. This reaches its nadir in the USA where extreme migrant hostility and nationalism was a key thread used by Trump in his election in 2016.  Since then he has enacted a whole host of policies that accelerate climate change. Climate change is a prime cause of migration from Central America to the US; and describing this migration as an ‘invasion’ and an ‘emergency’ is part of Trump’s re-election strategy. If he is successful it’s not hard to see how Populism -> Climate Change -> Migration -> Populism could form a positive feedback cycle.

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