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Climate scientist Will Steffen explains that continued warming of the atmosphere could trigger a cascade of tipping points

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DIMITRI LASCARIS: This Dimitri Lascaris, reporting for The Real News in Toronto, Canada.

A major new climate change study was published recently in the Proceedings of the U.S. National Academy of Sciences. The study, entitled Trajectories of the Earth System in the Anthropocene, posited that human activity is propelling us toward a planetary threshold that, if crossed, could prevent stabilization of the climate and intermediate temperature rises and cause continued warming on a hothouse Earth pathway even as human emissions are reduced. Crossing the threshold would lead to a much higher global average temperature than any interglacial in the past one point two million years and to sea levels significantly higher than any time in the Holocene era.

Now here to discuss this study with us is one of the coauthors, Dr. Will Steffen. Dr. Steffen is an Earth System scientist and emeritus professor at the Australian National University, Canberra, a Senior Fellow of the Stockholm Resilience Centre and a Counsellor with the Climate Council of Australia. He joins us today from Canberra, Australia. Thank you very much for joining us today.

WILL STEFFEN: Thank you, Dimitri.

DIMITRI LASCARIS: So, Dr. Steffen, before we get into the meat of the study, could you explain to us what is meant by the Anthropocene period and what this study has to say about the concept of an Anthropocene period?

DIMITRI LASCARIS: Well, the Anthropocene is a proposed new geological epoch that would follow one from Holocene. And it’s based on the evidence that we have gone well outside of Holocene norms in terms of the structure and functioning of the Earth system. It was first proposed in 2000 by a an Earth System scientist and has now been taken up also by the geological community. And they’re going through the process of formalizing the Anthropocene. So basically, it means we humans have changed the Earth system enough and particularly fast enough that we have left the eleven thousand seven hundred years stable period of the Holocene.

DIMITRI LASCARIS: And in your view, what are the major conclusions of the study, particularly for laypersons like myself? What should we take away from it?

WILL STEFFEN: Well, I think the main conclusion of the study is that the dominant narrative about climate change may need to be rethought. We normally think that the temperature rise and the level of climate change we will experience is proportional to our emissions. And that’s probably true at low levels of emissions and temperature rise, but we argue that the Earth as a complex system has inbuilt feedback processes. And if we start to trigger these feedback processes, they act like a cascade, like knocking down a row of dominoes. And once they start tipping and falling, we can’t stop them. That would take us to a much different climate, a much warmer climate, a much more difficult climate for humans to live in.

DIMITRI LASCARIS: So, the Paris Climate Accords, as I’m sure you know, Dr. Steffen, is a global- sets as an aspirational goal a global temperature increase maximum of two degrees Celsius over pre-industrial levels. And in your opinion, based on the evidence now available to us, what is the planetary threshold that, if crossed, could provide stabilization of the climate and intermediate temperature rises and cause continued warming on a hothouse Earth pathway. Is that threshold likely to be lower or higher than the aspirational goal of two degrees Celcius and the Paris Climate Accord?

WILL STEFFEN: Yeah, that’s a really critical question and one that is going to require more research. The way we put it is the Paris target actually is a range. It’s one point five to two degrees, and I think it says stay well below two degrees and aim to get as close as possible to one point five. What we understand so far about how the system operates, I would say that one point five degree temperature rise has a very low probability of triggering these tipping cascades that we’re talking about. So, it’s relatively safe. The probability wouldn’t be zero, but I think it would be relatively low.

If you go to the other end, if we go to a three or four degree temperature rise, which is where our current level of ambition or current level of policy around the world would take us, I think there’s actually a high probability that we would have crossed that threshold and be on the pathway to hothouses. Now, of course, there’s a range between one point five and three and four and two. I would say that it’s hard to pick whether we would cross the threshold at two. Obviously, there’s a higher risk than at one point five, but that’s an urgent research question, to do more to say just how safe or dangerous the upper degree target of Paris really is.

But I think this is really a risk analysis. It’s how much risk are we really willing to take? We may never actually pin down precisely where this cascade may start because we’re dealing with a very complex system, but we certainly know that it’s very, very feasible we can trigger it within the temperature ranges that we could reach this century.

DIMITRI LASCARIS: And does this study confirm or support the proposition that the Earth is more sensitive to warming than scientists had previously believed?

WILL STEFFEN: Yes, it does. And it does because much of the work that’s been undertaken up to now has not taken into account the strength of these feedbacks in the Earth’s system. A lot of them have been studied individually, offline so to speak, but most of them are not included in the climate model, so we actually can’t simulate where this cascade might be. But there is enough evidence, strictly from the way the earth has behaved in the past, the states of the Earth’s system we’ve seen in the recent past, say two or three million years ago or or even fifteen million years ago, the Earth was four or five degrees hotter. That’s not a long time ago in terms of Earth history.

So, there is a lot of evidence scattered out there that hasn’t yet been put together that indicates, yes, this is a very real risk that we are facing. And I think our paper was the first one to actually put all of this together in a very coherent way and say we better rethink the whole framing of the climate change challenge.

WILL STEFFEN: And lastly, Dr. Steffen, what in your opinion are the specific steps that we have to take in order to avoid crossing this critical threshold?

WILL STEFFEN: Well, the first thing we have to do is really make sure that we meet those Paris targets. Right now, they’re not be being taken seriously enough. If you look at the ambition that countries have put forward in the first INDC, their indicated National Contribution to the Paris Summit, that would take us to a three or three plus degree world, and that certainly is very dangerous territory. So, that needs to be ramped up very, very quickly.

Now, more specifically, the first thing we actually have to do absolutely is not to open up any new fossil fuel resources around the planet. In other words, no new coal mines, no new oil wells, no new gas- conventional or unconventional gas- that just has to stop. Then, we have to have a very, very definite phase out plan for the existing fossil fuel resources around the planet over about a two or three decade period. And of course, we replace that with renewables, we replace that with other types of transport systems run off electricity, run off biofuels.

So, a lot of the technical solutions that we need are actually out there. A point we make in our paper, though, is that all of these need to be underpinned by new value systems that value stabilising the Earth’s system as the highest priority that any economy must strive for. In other words, economic efficiency or GDP growth or things like that must take second place to stabilising the Earth’s system. So, there are a lot of tools out there that people have, there’s a lot of understanding of what we need to do, but we don’t yet have the value systems, the policy settings, the economic levers yet to do that.

And that’s an urgent challenge that we really have to solve over the next five or ten years if we want to have a chance, a really good chance, of avoiding this potential our hohouse pathway.

DIMITRI LASCARIS: Well, this has been Dimitri Lascaris speaking to Dr. Will Steffen, one of the coauthors of the major new study on the possibility of global warming taking us into a hothouse Earth scenario. Thank you very much for joining us today, Dr. Steffen.

WILL STEFFEN: Thank you, Dimitri.

DIMITRI LASCARIS: And this is Dimitri Lascaris reporting for The Real News Network from Toronto, Canada.

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Dimitri Lascaris is a lawyer that focuses on human rights and environmental law. He is the former justice critic of the Green Party of Canada and is a former board member of the Real News Network. You can follow him @dimitrilascaris and find more of his work at