Without effective action, planet may be on track for irreversible warming, study shows

Sun seen from Sebangau national park in Central Kalimantan, Indonesia is clouded with haze from smoke from peat fires. CIFOR/Aulia Erlangga
18 September 2018

BONN, Germany (Landscape News) — As sweltering temperatures and record numbers of wildfires affect people around the globe, a paper published in the Proceedings of the National Academy of Sciences provides a grim scientific backing to those concerns. According to its authors, our planet may be approaching a threshold past which any attempts to stop greenhouse-gas induced climate change will be futile.

“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,” states the paper, which was downloaded more than 270,000 times in the first few days after publication. “This pathway would be propelled by strong, intrinsic, bio-geophysical feedbacks difficult to influence by human actions, a pathway that could not be reversed, steered, or substantially slowed.”

“The standard framework for looking at climate change is a somewhat linear relationship,” explained Will Steffen, a professor at the Australian National University in Canberra, and the paper’s lead author.

Researchers conducted their investigations in the context of the 2015 U.N. Paris Agreement, which obliges countries to keep global warming to well under 2 degrees Celsius above preindustrial levels and to pursue efforts to limit increases to 1.5 degrees Celsius above preindustrial levels.

“If you look at the Intergovernmental Panel on Climate Change projections, they have a range of emission trajectories. The more you emit, the higher the temperature gets. The assumption is once we stop emitting greenhouse gasses, the temperature rise will stabilize. If we meet the Paris target and park the Earth at 2 (degrees) C, we can expect that it will just sit there at 2C. We are saying that the Earth probably will not behave that way.”

The planet has oscillated over millennia between glacial and interglacial periods. The transitions between them, said Steffen, are usually driven by so-called feedback processes.

“What we are arguing,” he added, “is that you can get to Hothouse Earth by fairly small additional human emissions of greenhouse gases if they trigger these feedbacks.”

Using a complex systems analysis, the scientists listed ten potential feedback processes. They include the massive potential release of methane trapped in Siberian permafrost, the weakening ability of drying forests to act as carbon sinks, and the impact of melting ice from a warming Greenland on the Antarctic as the Gulf Stream is disrupted.

The result – a planet less able to reflect heat or absorb carbon – could push the earth to temperature rises as high as 4 degrees Celsius.

“You can think of our analysis as a risk analysis,” said Steffen, “in terms of that, if we meet the lower of the Paris targets, 1.5C – and we assess it as a fairly low probability – we should be able to keep the earth at a relatively stable state at 1.5C. At 2C the risk is going up, and 3C is a very serious risk. In fact, in my view, the odds are that we probably will cross 3C. And by 4C, well, you are almost at a Hothouse Earth anyway. The really tricky terrain is between 1.5 and 3C. That is where the risk escalates.”

How close are we to a Hothouse Earth threshold? For Steffen, we are on the pathway to it. “I say that because we are still continuing to emit greenhouse gases at a very high level,” he said. “The problem has actually been well known for a long time, and yet emissions have still been creeping up over the last decade. So it is showing very clearly that we are not close to a Stabilized Earth Pathway yet.”

Making it onto a Stabilized Earth Pathway requires “effective Earth System stewardship,” according to the paper, and “is an essential precondition for the prosperous development of human societies.”

That implies lowering greenhouse gas emissions as quickly as possible, said Steffen. It means transitioning to renewable energies, electrifying transport systems and “really massively reorganizing agriculture so it doesn’t admit as much nitrous oxide through fertilizer and methane through rice and cattle production.”

While there has been some development of technologies that pull carbon dioxide out of the atmosphere, he added, they are both expensive and still very much at the idea stage.

“The bottom line is we need some very fundamental changes in our value systems,” he said, “in the way we organize our economies and politics to ensure that the number one issue, the number one driving force, has to be stabilizing the earth system.”

Steffen agreed that initiatives like the Bonn Challenge, which seeks to restore 150 million hectares of deforested land by 2020 and 350 million by 2030, “is absolutely consistent with what we are trying to say in this paper.”

Stopping deforestation, “is very important for our earth system approach because a couple of those big feedbacks with tipping points are in the terrestrial biosphere, the Amazon in particular, but also the vast boreal forests across Canada, Alaska and Siberia,” he said.