6 August 2018
Researchers believe we could soon cross a threshold leading to boiling hot temperatures and towering seas
By BBC
It may sound like the title of a low budget sci-fi movie, but for planetary scientists, "Hothouse Earth" is a deadly serious concept.
Researchers believe we could soon cross a threshold leading to boiling hot temperatures and towering seas in the centuries to come.
Even if countries succeed in meeting their CO₂ targets, we could still lurch on to this "irreversible pathway".
Their study shows it could happen if global temperatures rise by 2 deg C.
The scientists involved say the heating we've experienced until now and the increases that will likely occur in the next few decades could turn some of the Earth's natural forces, that currently protect us, into our enemies.
Each year the Earth's forests, oceans and land soak up about 4.5 billion tonnes of carbon that would otherwise end up in our atmosphere adding to temperatures.
But as the world experiences warming, these carbon sinks could become sources of carbon and make the problems of climate change significantly worse.
So whether it is the permafrost in northern latitudes that now holds millions of tonnes of warming gases, or the Amazon rainforest, the fear is that the closer we get to 2 degrees of warming above pre-industrials levels, the greater the chances that these natural allies will spew out more carbon than they currently now take in.
Back in 2015, governments of the world committed themselves to keeping temperature rises well below 2 degrees, and to strive to keep them under 1.5. According to the authors, the current plans to cut carbon may not be enough if their analysis is correct.
"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 Prof Johan Rockström, from the Stockholm Resilience Centre, told BBC News.
"We are the ones in control right now, but once we go past 2 degrees we see that the Earth system tips over from being a friend to a foe - we totally hand over our fate to an Earth system that starts rolling out of equilibrium."
Currently, global temperatures have risen about 1 degree above pre-industrial levels and they are rising by around 0.17C per decade.
In their new study the authors looked at 10 natural systems, which they term "feedback processes".
Right now these help humanity to avoid the worst impacts of carbon and temperature rises, and include forests, Arctic sea-ice, and methane hydrates on the ocean floor.
The worry is that if one of these systems tips over and starts pushing large amounts of CO₂ into the atmosphere, the rest could follow like a row of dominoes.
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.
The climate might stabilise with 4-5 degrees C of warming above the pre-industrial age. Thanks to the melting of ice sheets, the seas could be 10-60 metres higher than now.
Essentially, this would mean that some parts of the Earth would become uninhabitable.
The impacts would be "massive, sometimes abrupt and undoubtedly disruptive," say the authors.
The only upside, if you can call it that, is that the worst impacts may not be felt for a century or two. The downside is that we wouldn't really be able to do anything about it, once it starts.
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