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Faster climate change anticipated due to cascading “hothouse effect”

The pace of climate change could ramp up in the near future due to the “hothouse” effect which will see the Earth reach a climactic tipping point triggering rapid rises in the global temperature.

A new study published in Proceedings of the National Academy of Sciences claims that even if the carbon emission reductions called for in the Paris Agreement are met, the effect could still occur in the coming decades.

The hothouse effect occurs due to feedback mechanisms in the Earth’s climate acting “like a row of dominoes” which will then spin the world into a state of uncontrollable climate change. The “tipping elements” could turn natural carbon storage systems or “sinks” into powerful greenhouse gas emitters. Such processes include permafrost thaw; the loss of methane hydrates from the ocean floor; weaker land and ocean carbon sinks; the loss of Arctic summer sea ice and the reduction of Antarctic sea ice and polar ice sheets.

The threshold will be reached when average global temperatures are only around 2°C higher than in pre-industrial levels, new research suggests. They are already 1°C higher, and rising. Long term, the Hothouse Earth climate will stabilise at a global average of 4-5°C above pre-industrial levels, the study shows. If that happens, swathes of the planet around the equator will become uninhabitable, with sea levels up to 60m higher than they are today, threatening coastal cities.

A Hothouse Earth would pose “severe risks for health, economies, political stability, and ultimately, the habitability of the planet for humans”, the team of international scientists working on the study wrote.

Professor Johan Rockstrom, a leading member of the team from the University of Stockholm, Sweden, said: “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.”

The scientists wrote: “Our analysis suggests that the Earth system may be approaching a planetary threshold that could lock in a continuing rapid pathway toward much hotter conditions - Hothouse Earth. This pathway would be propelled by strong, intrinsic, biogeophysical feedbacks difficult to influence by human actions, a pathway that could not be reversed, steered or substantially slowed. Where such a threshold might be is uncertain, but it could be only decades ahead at a temperature rise of (around) 2°C above pre-industrial [levels].”

Avoiding a Hothouse Earth would require “deep cuts” in greenhouse gas emissions as well as concerted efforts to remove carbon dioxide from the atmosphere, both by preserving natural carbon sinks and using technology, said the researchers.

Commenting on the findings, climate researcher Dr Phil Williamson, from the University of East Anglia, said: “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.”

Chris Rapley, Professor of Climate Science at University College London said: “Previous research has shown that an increase in the mean global temperature of 11-12°C would make more than half of the land area currently occupied by humans uninhabitable. So, a ‘runaway’ warming to a new and uncontrollable hot state would represent an existential threat to humanity and the majority of existing species.”

Last month a study showed that humans are already adapting to the impact of climate change, with heat deaths in Spain decreasing over the last 35 years despite steady increases in temperature. 

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