‘Hothouse Earth’: What is it and what can we do about it?

This week, an international team of scientists published a new study, suggesting we are now dangerously close to the tipping point for a “Hothouse Earth”.

While that might sound like an almost humorous term, it describes an entirely new climate system, characterized by natural feedback loops that could bolster global warming, despite emissions reductions and entirely outside of human control. A “Hothouse Earth” climate will in the long term stabilize at a global average of 4–5°C higher than pre-industrial temperatures with sea level 10–60 meters higher than today, the paper says.

We have known about climate feedback loops for a while now, but what was revolutionary about this study is the finding that what we had previously deemed a ‘safe’ maximum level of human induced warming—2 degrees celsius—may in fact push us over into the Hothouse scenario.

Back up—What do you mean feedback loops?

Each year the Earth’s ‘carbon sinks’—forests, oceans and land—soak up about 4.5 billion tonnes of carbon that would otherwise end up in our atmosphere. But as the world continues to warm due to human-emitted carbon in the atmosphere, these natural systems could become sources of more carbon by releasing their reservoirs, therefore causing even more warming.

Graphic from the Stockholm Resilience Centre

Consider permafrost near the Arctic, which now holds millions of tonnes of warming gases, safely stored under permanent ice sheets; in case they continue to melt, those gases could be released into the atmosphere and have significant impacts on our current projections for future warming.

The Amazon rainforest is another example of a massive reservoir of carbon and one of the largest carbon sinks on Earth, absorbing about 2.2 billion tonnes of carbon dioxide every year. But even this massive system is already declining in its absorption capacity, now taking in a third less carbon than a decade ago. As it continues to experience deforestation and degrading, the organic matter contained in such a vast system could potentially also be released into the atmosphere in the form of carbon dioxide.

Ice sheets are an example of positive feedback loops when it comes to the climate system. The vast white surface of ice in the poles serves as a reflecting surface that mitigates the amount of solar radiation absorbed by Earth. But as they melt due to climate change, the absence of white ice in turn causes more warming.

“What we are saying is that when we reach 2 degrees of warming, we may be at a point where we hand over the control mechanism to Planet Earth herself,” co-author Johan Rockström, from the Stockholm Resilience Centre, told BBC News for their coverage.

What would a hothouse world look like?

In short, not good.

According to the research paper, crossing into a Hothouse Earth period would see a higher global temperature than at any time in the past 1.2 million years; with the climate stabilizing at around 4–5 degrees celsius above pre industrial levels, resulting in 10 to 60 metres of sea level rise.

This would make some parts of the world uninhabitable, with impacts that would be “massive, sometimes abrupt and undoubtedly disruptive,” according to the authors. Worse of all, we would have absolutely no control or action path to reverse it once we cross that threshold.

What are people saying about this?

The media has been quick to jump onto the “doomsday scenario” narrative that has done us no favors in the past, when covering this new report, failing to recognize what should be the real story here: there is still something that can be done to prevent this.

In a tweet, Diana Liverman, a co-author of the paper said, “Clearly people aren’t reading the paper we wrote where our point is exactly that Hothouse Earth is not our destiny and that social system feedbacks are starting to move us to the Stable Earth. But media goes for worst case and makes it sound certain.”

Reporting on climate projections as if they are unavoidable only perpetuates the problem by fostering hopelessness. It is an issue that has plagued climate activists and advocates since there has been such as thing.

It is something I certainly spend a lot of my time thinking about and as an office we discuss regularly: How do we convey the gravity of the climate crisis while at the same time projecting a message that inspires action rather than resignation?

Our job is pretty much to show others that there is a fire and convince them to come help put it out. But people run away from fire, not towards it. And that is where I think we are getting things wrong. We cannot throw our hands in the air and accept that our fate will be a Hothouse planet that does not sustain life as we know it.

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