The planet urgently needs a transition to a green economy because fossil fuel pollution risks pushing the Earth into an irreversible and dangerous “greenhouse” state , a team of experts has warned.
If polar ice continues to melt, forests shrink, and greenhouse gases rise to new levels, as they currently do every year, the Earth will go through a tipping point.
An international team of scientists has published a study in the journal Proceedings of the National Academy of Sciences (PNAS) which shows that even if the carbon emission reductions required in the Paris Agreement are met, there is a risk that the Earth enters in what scientists call a “Greenhouse Earth” state. The climate of this “Greenhouse Earth” will stabilize in the long term at a global average 4-5 ° C higher at pre-industrial temperatures with a sea level 10-60 meters higher than today. The authors conclude that it is very urgent to accelerate the transition to an emission-free global economy.
“Human emissions of greenhouse gases are not the only determinant of temperature on Earth. Our study suggests that human-induced global warming of 2 ° C may trigger other processes, often called ” feedbacks. ” , which can lead to further warming if we do not stop emitting greenhouse gases. Avoiding this scenario requires a redirection of human actions from exploitation to the administration of the Earth system “, comments Will Steffen of the Australian National University and Stockholm Resilience Center and leader of the work.
Stage
A cascade of melting ice, warm seas, shifting currents and dying forests could turn Earth into a “greenhouse” where human efforts to reduce emissions would become increasingly futile.
This grim prospect is outlined in the paper, which considers the combined consequences of 10 climate change processes , including the release of methane trapped in Siberian permafrost and the impact of melting Greenland ice on Antarctica.
The authors stress that this path “would almost certainly flood delta environments, increase the risk of damage from coastal storms, and eliminate coral reefs (and all the benefits they provide to societies) by the end of this century or earlier .”
“I hope we are wrong, but as scientists we have a responsibility to explore whether this is real. We need to know now,” explains Johan Rockström, executive director of the Stockholm Resilience Center and co-author of the study.
Previous studies have shown that weakening carbon sinks will add 0.25ºC, forest extinction will add 0.11ºC, permafrost thaw will add 0.9ºC and increased bacterial respiration will add 0.02ºC.
Rockström says there are huge gaps in data and knowledge about how one process can amplify another. Contrary to the Gaia theory, which suggests that the Earth has a tendency to self-correct, it says that feedbacks could push the planet into a more extreme state.
As an example, the authors say that the loss of ice from Greenland could alter the ocean current of the Gulf Stream, raising sea levels and accumulating heat in the Southern Ocean, which in turn would accelerate the loss of ice from East Antarctica.
Currently, global average temperatures are around 1ºC above pre-industrial levels and increasing to 0.17ºC per decade . The Paris climate agreement established actions to keep warming limited to 1.5C-2C by the end of the century, but scientists warn that more drastic action might be necessary.
“The heat wave that we have now in Europe is not something to be expected with just 1 ° C of warming,” says Rockström. “Several positive feedback loops are already in place, but they are still weak. We need more studies to show when they could cause a runaway effect .”
Citation: Will Steffen, Johan Rockström, Katherine Richardson, Timothy M. Lenton, Carl Folke, Diana Liverman, Colin P. Summerhayes, Anthony D. Barnosky, Sarah E. Cornell, Michel Crucifix, Jonathan F. Donges, Ingo Fetzer, Steven J Lade, Marten Scheffer, Ricarda Winkelmann, and Hans Joachim Schellnhuber. Trajectories of the Earth System in the Anthropocene . PNAS , 2018 DOI: 10.1073 / pnas.1810141115
