Despite the pledges and measures being taken to address the rising concentrations of atmospheric carbon dioxide, CO2 levels continue to climb. This trend is causing concern amongst climate researchers, including worries that limiting global warming’s effects to two degrees Celsius, as per the Paris Agreement, might still trigger a cascade effect that would lead to a "Hothouse Earth" situation that we would have no control over.

A joint study from the Stockholm Resilience Centre, the University of Copenhagen, Australian National University and the Potsdam Institute for Climate Impact Research, warns about just such a runaway climate scenario, a situation where global average temperatures could reach 4-5°C. The study warns that if a critical threshold within the climate is reached, it cold trigger the tipping-points of a number of climate mechanisms, such as the release of methane, a powerful greenhouse gas, from melted permafrost; increased warming due to the loss of summer sea ice in the Arctic, resulting in less solar radiation being reflected back into space; and the loss of natural carbon sinks, such as large forests.

"These tipping elements can potentially act like a row of dominoes. Once one is pushed over, it pushes Earth towards another," explains Johan Rockström, co-author of the report and executive director of the Stockholm Resilience Centre.

"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," Rockström continues.

The study says that successfully curbing CO2 emissions might not be enough to prevent Earth’s climate from falling victim to such a domino effect, and that other steps may be necessary to address the problem. Measures such as biodiversity conservation; improved agricultural, soil and forest management; and carbon dioxide sequestration technologies will be needed if we are to maximize our chances of keeping Earth’s climate under control.

The National Oceanic and Atmospheric Administration reports that global CO2 concentrations hit an average of 405 parts per million in 2017 — that’s 35 percent higher than the highest levels seen over the past 800,000 years, and 45 percent higher than the pre-industrial average, the levels human civilization has been comfortable with for the entirety of its history.

The continued string of record-breaking temperatures being experienced across the globe this year is illustrating that global warming and its effects are to be taken seriously. Although not involved with the study, University of East Anglia climate researcher Phil Williamson warns that, "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."

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