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Planet at risk of becoming 'Hothouse Earth'

CLIMATE CHANGE resulting from human activities has made heatwaves like the one just experienced across Europe twice as likely to occur, according to a group of scientists. Researchers compared the current high temperatures with historical records from seven weather stations, in different parts of Europe. Their preliminary report found that the “signal of climate change is unambiguous” in this summer's heat. They add that the intensity of the current heatwave in the Arctic is unprecedented.

To try and see if there is a connection between human-influenced global warming and this summer’s heatwaves, researchers looked at data from seven weather stations, in Finland, Denmark, Ireland, the Netherlands, Norway and Sweden. They chose these locations because they all had digitised records dating back to the early 1900s, unlike the UK. The team also used computer models to assess the scale of human-influenced climate change. The researchers found that in the weather stations in the Netherlands, Ireland and Denmark, climate change has generally increased the odds of the current heatwave by more than two-fold. The scientists, from the World Weather Attribution group, say they will formally publish their findings later in 2018.

They estimate that in southern Scandinavia it's likely there will be a similar heatwave every 10 years, while further south, in the Netherlands, it's likely to be once every five years. This ties in with projections from several scientists that the type of heatwave we've had this summer could occur every second year by the 2040s. "The logic that climate change will do this is inescapable - the world is becoming warmer, and so heatwaves like this are becoming more common," said Dr Friederike Otto, from the University of Oxford.

In a related development, an international team of scientists has published a study in Proceedings of the National Academy of Sciences (PNAS) showing that even if the carbon emission reductions called for in the Paris Agreement were to be met, we would still risk the entire planet entering ‘Hothouse Earth’ conditions.

The authors consider ten natural feedback processes, some of which are tipping elements that lead to abrupt change if a critical threshold is crossed. Each of these planetary mechanisms could turn from being a ‘friend’ capable of storing carbon to a ‘foe’ that starts to emit it uncontrollably in a warmer world.

These processes include:

  • the thawing of permafrost in regions such as Siberia, releasing huge quantities of the greenhouse gas methane;

  • loss of methane hydrates from the ocean floor;

  • weakening land and ocean carbon sinks;

  • increasing bacterial respiration in the oceans of the world, limiting their ability to store carbon;

  • forest dieback;

  • loss of Arctic and Antarctic snow cover, sea ice and polar ice sheets.

The authors explain that each year, the Earth’s forests, oceans and land have been soaking 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 are set to become active sources of carbon emissions, no longer helping but making the problems of climate change significantly worse.

Whether it is the permafrost in northern latitudes that now holds millions of tonnes of warming gases, or the Amazon rainforest which takes carbon out of the air, the problem is that the closer we get to two degrees of warming above pre-industrial levels, the greater the chances that these natural allies will spew out more carbon than they currently take in.

One author of the PNAS study explains: “These tipping elements can potentially act like a row of dominoes. Once one is pushed over, it pushes Earth towards another. It may be very difficult or impossible to stop the whole row of dominoes from tumbling over. Places on Earth will become uninhabitable if ‘Hothouse Earth’ becomes the reality.”

According to another of the authors: “We show how industrial-age greenhouse gas emissions force our climate, and ultimately the Earth system, out of balance. In particular, we address tipping elements in the planetary machinery that might, once a certain stress level has been passed, one by one change fundamentally, rapidly, and perhaps irreversibly. This cascade of events may tip the entire Earth system into a new mode of operation.”

Maximising the chances of avoiding a Hothouse Earth requires not only dramatic and immediate reduction of greenhouse gas emissions, but also the creation of new biological carbon stores, for example, through improved forest, agricultural and soil management; biodiversity conservation; and technologies for removing carbon dioxide from the atmosphere and storing it underground.

Critically, the study emphasises that these measures must be underpinned by fundamental social and political changes if we are to avoid tipping the planet’s interrelated ecosystems toward ‘Hothouse Earth’.

For too long, activists on the left have argued that although green issues may be important in the long term, they are less pressing and immediate than the many bread-and-butter issues regularly faced by the working class. It is time to turn these assumptions round.

The alarm bells are now ringing loud. Not just for the future of our children and grandchildren but for our everyday peace of mind, few issues can be more immediate and pressing than whether we are letting turbo-capitalism burn up the only planet we have.

  • Chris Knight is a research professor at University College London

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