An international team of climate scientists warns that the global climate is close to its tipping point. Their report, ‘’Trajectories of the Earth System in the Anthropocene,’’ was published in the American Proceedings of the National Academy of Sciences. As the scientists point out, feedback processes could trigger irrevocable changes in the climate system which could lead to a situation referred to as “Hothouse Earth”.
As Will Steffen, the lead author from the Australian National University and Stockholm Resilience Centre, explains, “Human emissions of greenhouse gas are not the sole determinant of temperatures on Earth. Our study suggests that human-induced global warming of 2°C may trigger other Earth system processes, often called ‘feedbacks’ that can drive further warming – even if we stop emitting greenhouse gases.”
On the current path, the planet is set to exceed the threshold in a few decades. Even if the emission reduction goals of the Paris Agreement were met, this might still not be sufficient to avoid “Hothouse Earth” conditions. In a ‘’Hothouse Earth’’, temperatures are expected to rise 4 to 5°C and sea levels will rise 10-60 meters above today’s levels. If this were to happen, this planet would be uninhabitable.
Findings from the report suggest that the Earth System is already on a trajectory towards hotter climatic conditions and away from the glacial-interglacial limit cycle. In a warmer world, the collapse of natural carbon sinks due to for example permafrost thaw, loss of methane hydrates from the ocean floor or dieback of forests may have a ‘’domino effect.’’ These effects mutually aggravate themselves, leading to the “Hothouse Earth”. A warmer planet would cause frequent and stronger extreme events such as heat waves, droughts and floods. It would also disrupt economies and ecosystems.
However, the news is not all gloom. Collectively humanity can steer the system away from its current path back to Holocene-like conditions. Deliberate and radical actions are necessary to create feedbacks that keep the system on a stabilized pathway. These actions entail – as the authors point out – transforming behavior and social values, adopting new institutional arrangements and decarbonizing the global economy using technological and carbon sinks. Yet, the authors note that within a short time frame of 50 – 100 years, only a few changes are reversible while most are irreversible in a time frame that is relevant to the current human society.
This report comes after the state of climate change in 2017 report published by the U.S. National Oceanic and Atmospheric Administration (NOAA) found that an increase in the amount CO2 emissions into the atmosphere corresponded to rising global temperatures in 2017.