Climate expert, Australian National University emeritus professor and Climate Council member Will Steffen spoke to Alex Bainbridge about climate science and politics in the lead up to the COP26 United Nations climate summit in Glasgow.
Your work has included a focus on the idea that there might be a series of cascading climate tipping points that lead to the development of ‘Hothouse Earth’. Can you explain this?
Tipping points are processes, or features, of a system whereby if you put stress on them, they change bit by bit, and reach a critical point where a small increase in pressure can lead to an unexpectedly large response.
Sometimes those responses are irreversible on time frames that are useful to us. Sometimes you can cross a tipping point and the system doesn’t seem like it’s changing any faster, but it reaches a point where you can’t stop it from changing.
Arctic sea ice, which is the ice floating over the Arctic Ocean, is an example of the latter. As the climate warms, it is retreating. In the Northern Hemisphere summer, as it shrinks it uncovers more dark ocean water that absorbs more sunlight, increases the heating and the ice shrinks a bit more. So, it’s shrinking a bit, year by year. But it’ll get to a critical point where, even if we can stabilise global average temperature, the fact that it’s uncovering more dark ocean water every summer means it will continue the process and it will basically disappear.
It may not speed up a whole lot, but it will be irreversible.
Greenland ice sheets are another example. They are melting from the top, as well as losing some from its outlet glaciers. But, as it melts from the top, it is lowering in elevation into warmer climatic zones and it will reach a point — where again — even if we stabilise the climate, it’ll just keep dropping until it virtually disappears.
Coral reefs are another good example of a temperature tipping point and the Amazon forest another. The point is that many are linked in various ways.
The best way to look at it is to start with what we talked about before — the Arctic sea ice. As that shrinks it is uncovering darker ocean water that is absorbing more sunlight during summer. This means it’s increasing the heating regionally in the northern high latitudes. That, in turn, is increasing the melt of the Greenland ice sheet.
So here you see a connection between two tipping points.
But what is Greenland doing? Well, it’s melting from on top. That means it is pouring fresh water into the North Atlantic Ocean and that is influencing the Atlantic Ocean circulation system. We can already measure a slowdown in the North Atlantic circulation system.
What does that do? It changes rainfall patterns of continents next to the Atlantic Ocean and it has an effect all the way down toward the equator.
In fact, one of those effects is to reduce rainfall over the Amazon Forest and when you do that, and you combine it with direct human pressures, you get an increase in loss of that forest and that may reach a critical tipping point.
That’s an example where four different tipping points — Arctic sea ice, a Greenland ice sheet, Atlantic Ocean circulation and Amazon rainforest — are all connected.
From these various connections — although they don’t form a neat row of dominoes entirely — one can lead to another, we are concerned that there is a risk that if enough of these start tipping, the Earth system itself will move to an essentially different state.
That’s how complex systems actually do transition from one state to another quite commonly.
It’s usually a combination of factors that push them out of a stable state into an unstable trajectory, until they settle down into another stable state.
There is a risk for the Earth system that we do need to take seriously.
Climate politics in Australia are so conservative that politicians are talking about net zero by 2050 as if that is a major advance. Is it?
No, net zero by 2050 won’t cut it. That’s far too late. We have to act with much more urgency. How close are we to a global tipping point, or initiating some sort of cascade? We don’t know and we probably never will know.
The best quote I can give you is from Carlos Nobre, a colleague and good friend. He is the former head of the world climate research program. He’s a Brazilian and his area of expertise is the Amazon rainforest. A lot of people ask him: “How close are we to a tipping point of the Amazon forest?” His answer is: “Well, I can’t tell you for sure. I think we’re closer than we suspect we are. But where that tipping point precisely lies, the only way we’ll know that for sure is by tipping it.” Then he said: “And, that’s not a very intelligent thing to do”.
The point I make is: we will never know for sure where a potential tipping cascade will be initiated — at what level of human pressure — it will probably be a combination of climatic pressure plus some local pressures on forests and so on. We’ll only know after we’ve tipped it and we see that it’s that it’s underway and then it’s too late.
So, you really need to take a risk analysis.
I think the Intergovernmental Panel on Climate Change (IPCC) Sixth Assessment Report was quite good in the summary for policymakers by putting some real high-end risks in.
For example, a 15-metre sea level rise by 2300. That’s a huge sea level rise — but they said we can’t rule it out. That was the terminology they used: there are some things we can’t rule out. We think they’re low probability but they’re extremely high impact and we can’t rule them out so you better take them seriously.
I think that’s the appropriate way to look at a tipping cascade, Hothouse Earth — we can’t rule it out.
The Earth has been 4–5°C hotter in the past; we know it can exist in that state. But we don’t know for sure where we might trigger such a transition, a tipping cascade. So the risk analysis says stay away from any potential tipping point as far as you can to safeguard the future. That’s the approach you need to take.
Australia lags far behind many other rich countries’ climate targets. United States President Joe Biden is on 50% by 2030; the European commission is saying 55%; British Prime Minister Boris Johnson is talking about a 78% reduction (from a different starting point) by 2035. Even the Business Council of Australia is calling for a 46–50% reduction by 2030. But are these other targets an adequate response to the risk assessment?
They point us in the right direction and reduce the risk. Globally, we need to cut emissions at least by 50% by 2030. That’s a minimum and we should aim for better. We should reach net zero by 2040, not 2050. Again, that’s the minimum. If we can do it a few years before that, the better we’ll be.
When you look at the so-called carbon budget for a trajectory like that, we’ll probably get close to 1.5°C but we won’t keel it below that because we’ve left it too late. We will hopefully keep the temperature rise to well below 2°C — between 1.7–1.8°C. That’s not altogether safe, and there will be pretty serious impacts but at least, from where we sit today, that will minimise the risk.
Even with that scenario, it won’t totally eliminate the risk of a tipping cascade. But we have a much higher risk of really bad outcomes if we stick with a net zero by 2050, than a weak 2030 target.
Net zero by 2050 is a cop-out: it’s kicking the can down the road.
We really need to look very carefully at what countries are pledging by 2030 and when they really need to hit net zero and it’s got to be well before 2050.
Turning to the ‘bright siding’ versus ‘alarmism’ debate, American climatologist and geophysicist Michael Mann said that ‘doom-ism’ is the new denialism. Others, including climate scientists and science communicators, talk like we’re on a sort of climate-heating global superhighway which is aiming for the 1.5°C exit but that, if we miss it, we’ll go 2°C, or 2.5°C. What are your thoughts?
My response to that more comes from my personal background than any expert understanding of “doomism” or “alarmism versus bright siding” or “sunshine pumping”.
That’s because I was a high altitude mountaineer, where the danger is right in front of you. There are a lot of objective dangers that you cannot control: they’re there in crevasses; weather shifts and so on.
You absolutely have to understand risks as clearly as you possibly can, which then makes it much easier to take the most appropriate action to minimise that risk.
While I’m not sure exactly what Michael Mann means about denialism or alarmism, we need to understand risk clearly and that means we shouldn’t sugarcoat it because that’s going to lead to poor decisions.
We need to say, “All right, things look really bad, there’s some really big risks out here but you have to take the next step”.
As a climber, what actions are you going to take to minimise those risks? Where do you turn back on a climb? Where do you say, “I think the risks are manageable?”
The reason I’m still here, at 74, is that I made the right decisions in several situations where I could have lost my life.
That’s the way we need to think. We need to be absolutely clear-minded about what these risks really are, and we need to have the best science to understand them.
We shouldn’t deny them, or sugarcoat them, or try to push them in the background. We have to take the next step of empowering people to say “This looks pretty bad. What do we do to get the best possible outcome we can?”
I’m saying that [reducing warming to] 1.5°C [above pre-industrial levels] is virtually impossible. But well below 2°C is not — and there’s a huge difference.
Every tenth of a degree is really important. There’s an enormous amount to gain; there’s an enormous amount we can still avoid. But the clear-eyed view is we can’t go back and pat ourselves on the back and say we avoided a lot there — we haven’t yet.
The second point I make is we have to act. How do you get people optimistic? You don’t do it by telling them good news or sunshine pumping — you do it by acting.
That’s also how you solve a big climbing problem: you act with the best understanding, with the best skills you’ve got and with timing. You’ve got to do all that, and trust your climbing mates.
We’ve got to do this with climate — we’ve got to act with the best. We know we’ve got to act vigorously, fast, with determination and consistently. That’s where governments have let us down.
But we, as citizens, really need to push them and say “Look, our future depends on this. You can’t fiddle around with short-term politics. We need to move on this now”.
There seems to have been a shift with more scientists speaking out on climate. Is that your assessment?
Absolutely. We see shifts even in the IPCC. The wording in Special Report: Global Warming of 1.5°C Summary for Policy Makers is quite different from earlier ones. The rock solid science is there, and the risk analysis is very clear in that report. It is something we are obliged to do as scientists: to put the risks on the table.
COP26 is almost upon us. Do you have any comments about policy directions for this country?
Obviously the policies are far too weak; everybody knows that. There are some fairly interesting arguments going on within the Coalition government, but time is running out. Scott Morrison has come up with a net zero target by 2050. But the real focus needs to be on what we do by 2030.
The second point is that, as the International Energy Agency (IEA) said, we have to stop investing in new fossil fuel projects of any kind: coal, oil or gas. The IEA is pointing the finger mostly at Australia. We can’t hide behind the fact that, if we export it, it’s somebody else’s problem. No, it’s our problem because we control the deposits of fossil fuels. We can choose to not exploit them and we can choose to develop renewables instead. That’s within our remit and that’s what we need to do.
I would like to see a focus on two things: one is, at least, 50% reduction by 2030. I would like to see it much higher. The Climate Council is reckoning that 75% is a challenge but it’s achievable. We should aim high. But, more importantly, we should absolutely put the brakes on fossil fuel development. No more, full stop.
People make judgments about campaigns based on assumptions about what they believe is possible. For me, climate change is the one issue that turns everything on its head and therefore we need to go all out to stop catastrophic climate change it as fast as we can.
The laws of physics don’t pay any attention to politics. This planet operates on the laws of physics, chemistry and so on. Natural scientists are giving advice based on the best science: politics better listen because the natural world doesn’t compromise like politicians do.
[Listen to a video of this interview here.]