Climate special: the past and future of the Earth's climate

Host: Benjamin Thompson

Welcome back to the Nature Podcast. This week, reconstructing the last 24,000 years of the Earth’s climate.

Host: Shamini Bundell

And the latest updates from COP26. I’m Shamini Bundell.

Host: Benjamin Thompson

And I’m Benjamin Thompson.

[Jingle]

Host: Benjamin Thompson

So before we start the show today, a very quick announcement. This is the 700th edition of the Nature Podcast.

Host: Shamini Bundell

Hooray!

Host: Benjamin Thompson

Quite the milestone, I think you’ll agree, and huge thanks to everyone who has helped to make the podcast what it was and is over the last 16 years.

Host: Shamini Bundell

Happy 700^th anniversary to us. On today’s show, we’re actually going to be looking at all things climate. So, coming up, we’ll have a special Briefing chat direct from COP26, finding out what’s been going on at this extremely important climate conference, and looking at the measures being discussed to tackle future warming.

Host: Benjamin Thompson

Up first, though, we’re going to look back into the Earth’s climatic past. This week in Nature, there’s a paper piecing together what’s been going on since the Last Glacial Maximum, about 20,000 years ago, and the team behind it have gone about it in a rather different way than others have tried. As Matt Osman from the University of Arizona, one of the authors of the paper, explains, Earth was rather different back then.

Interviewee: Matt Osman

From a geologic perspective, right, so our planet is some 4.6 billion years old, this really wasn’t so long ago, but it was effectively a different world than the one we live in today, right? So, global sea levels were about 130 metres lower than present. Greenhouse gases were about half that of modern-day values. Canada, Northern Europe, the Himalayas, were each covered by some 2,000-4,000 metres of ice. But we’ve long been interested in this transition from this different world to the one we live in today from a climatic perspective because these were really massive changes that occurred.

Interviewer: Benjamin Thompson

Researchers want to know how the global climate responded to these massive changes. They hope that by understanding what happened in the past, they might have more insight into where we’re headed in the future. To get a sense of what was going on, in this work, Matt has been looking at surface temperatures around the globe. Now, of course, thermometer records only go back a few hundred years, so working out what temperatures were like further back is tricky. Broadly speaking, there are two ways to do it. One uses complex models run on big computers that bring together physics and chemistry and simulate the planet’s processes. The other uses so-called ‘proxies’.

Interviewee: Matt Osman

A proxy of climate is an indirect recorder that we have of how the climate has changed in the past, right? For example, in our study, what we did is we used sediments found at the ocean floor, and in particular what we did is we extracted signals that were recorded by ancient phytoplankton and subsequently buried within ocean sediments. So, we took these marine geochemical signatures and we applied calibrations for how those signatures vary with temperature to understand past climate change.

Interviewer: Benjamin Thompson

Both of these techniques have their pros and cons. Models cover the whole globe but are often based on best assumptions. Proxies, on the other hand, show what was going on in a specific location but can be limited in where they’re found and how far back they go. And these differences mean that the two methods can come up with different answers. A lot of research has been done at the interface between the two, and that’s what Matt’s work is about. He and his colleagues have been working for a long time to combine apples with oranges.

Interviewee: Matt Osman

This is a technique known as data assimilation. It’s essentially combining together observations of what the climate system is doing with what model physics predict, right? So, we’ve been using this technique, for example, in weather forecasting for at least a couple of decades at this point. The timescales that we’re thinking about for those applications are much shorter. We’re talking about days to no more than a couple of weeks. In the past few years, methodological as well as technological advances have allowed us to start to essentially smush together these large compilations of climate proxies we have going back hundreds of years with these climate model simulations that cover the same time. What we’ve done is we’ve applied the same principles but we’ve gone way further back in time. We’ve gone back 24,000 years, so much further back into the past than what prior applications have been able to show.

Interviewer: Benjamin Thompson

By using this hybrid approach, the team could get the best of both worlds. They used more proxies from previous work, taken from specific marine locations, each spanning at least 4,000 years. These helped to enhance a climate model with what was actually going on, and this model could then fill in the gaps for where and when there weren’t proxy values available. Another thing the team were able to do was split the entire record up into 200 year chunks to give a sense of how the climate evolved over the 24,000 years. Shaun Marcott from the University of Wisconsin-Madison, who’s co-authored a News and Views article about the work, was impressed and says that the new paper gives other researchers something to compare their results to.

Interviewee: Shaun Marcott

For anyone, let’s say, that’s working on ice sheet reconstructions or paleoenvironmental reconstructions at their location, you now have this template that you can compare your data or maybe map it back onto. That’s what’s amazing about this paper. It’s basically giving the community this beautiful reconstruction in 200-year slices. It’s exactly what we’re trying to do as a larger community.

Interviewer: Benjamin Thompson

This work provides a new take on changes to the Earth’s temperature over the last 24,000 years. And the results are likely to cause some debate in the field. For example, about 9,000 years ago, it suggests a small but consistent warming in global average temperatures up to the pre-industrial era, which was not shown in other proxy-only methods, including one Shaun was involved in, which suggested there was cooling during this time. For Shaun, though, this new paper doesn’t represent a conclusion to debates like this, rather it’s the start of a new way of piecing together past temperatures.

Interviewee: Shaun Marcott

I think this is the beginning, this analysis, of the way people who do this work will maybe approach the science. That’s really what I think is another one of the hallmarks of this paper, is a different approach, and I think that future studies will try to replicate this and will certainly get different results. It was one model that was used. We’ll want to, of course, use different models. And the datasets don’t span everywhere. There are no terrestrial data in this particular dataset. So, I think that that will inspire other people to incorporate those, and I think this will begin a new chapter in what we do as a community, in a sense of how we approach this question of global climate change of the last 20,000 years.

Interviewer: Benjamin Thompson

Matt too thinks that using other models and other proxies will help refine the results this method produces, and he wants to take things even further.

Interviewee: Matt Osman

The Earth is really old. We have 4.6 billion years of history that we can potentially use to start to disentangle and understand how the climate system fundamentally works. These techniques, provided that we have proxies, provided that we have models, allow us to go back into really, deep interesting periods of Earth’s history and to start to pick apart these changes in order to inform our future.

Interviewer: Benjamin Thompson

But what does the past tell us about the future? For Shaun, this new paper puts things into context and suggests that the temperatures we’re seeing now, and are expected to see in future, show that we really are living in unprecedented times.

Interviewee: Shaun Marcott

The past record provides perspective. Papers like this basically point out, just at the very basic level, what has happened before and where we are in that context and where we’re heading towards. In a prior paper that we had, we said statistically we don’t really know if today is any warmer than what we call the warm period of the last 10,000 years. This paper has said actually, we’ve left what was normal. That’s an important perspective to have when you think about where we’re off to, considering these temperatures that we’re trajecting towards, as far we know, we haven’t seen in 50 million years or so, and the world was a lot different then.

Interviewer: Benjamin Thompson

That was Shaun Marcott from the University of Wisconsin-Madison in the US. You also heard from Matt Osman from the University of Arizona, also in the US. You can find links to Shaun’s News and Views article and Matt’s paper over in the show notes.

Host: Shamini Bundell

Up in Glasgow, here in the UK, the 26th UN Climate Change Conference or COP26 is in full swing, and politicians, scientists and activists from all over the world are there.

Host: Benjamin Thompson

Yeah, that’s right Shamini. This is the second week of COP now, and there has been a huge amount of news coming out of the event.

Host: Shamini Bundell

Of course, last week, Ben, you were reporting from the train to COP. Well, this week, we have reporters on the ground at the conference and to give us a sense of what’s been happening, we’re going to hand over to our very own Nick Petrić Howe who’s been speaking with Flora Graham, senior editor of the Nature Briefing.

Interviewer: Nick Petrić Howe

Thanks, Shamini. That’s right, I’m here in Glasgow, as you may be able to tell from all the sort of hustling and bustling that’s going on in the background. Flora, how is it going?

Interviewee: Flora Graham

I have to be honest, I’m finding it really inspiring. It feels like the kind of utopian, aspirational world. All of the cups are reusable, all of the masks are being worn. It’s a good feeling so far.

Interviewer: Nick Petrić Howe

I think a good place to start in our sort of conversation about COP is to probably do a bit of a recap. What’s happened? What are the major things that have occurred so far?

Interviewee: Flora Graham

Well, I think a lot of us who are following climate policy were a little surprised by how much has already come out of COP. Often things come more towards the end of these meetings, but we really did hear a lot in the first week. So, we heard from India, a new net-zero target in 2070, which is very interesting and exciting. That’s a country that’s going to face huge challenges, so maybe it’s no surprise that they are giving themselves a couple more decades than some of the richer nations. We also heard a lot about reducing methane emissions. So, we know that methane, although it’s a tiny fraction of the total emissions of greenhouse gases, has a very powerful effect on global warming, and on the kind of good side, it disappears from the atmosphere more quickly than carbon dioxide. So, the quicker we can reduce methane, the quicker we can have a very quick win on climate. Of course, that’s not to say that reducing other emissions is not vitally important.

Interviewer: Nick Petrić Howe

And this event is very policy-heavy, a lot of negotiations, a very nitty gritty sort of politicking going on, but it’s closely followed by scientists from across the world. What’s been their reaction?

Interviewee: Flora Graham

I would say extremely cautiously optimistic. Of course, there’s going to be huge variation between scientists as there are between anybody. I would say people were pleasantly surprised to hear India’s bold climate pledge. I think people are very supportive of the idea of methane reduction, especially in the United States where new regulations have been brought in to actually achieve that. So, if you look at what scientists told us, in Nature you can read about what scientists think about the conference so far, and there are a lot of moments of hope. One of the big ones is to hear biodiversity and climate change being mentioned in the same sentence. The UN has often treated those topics very separately, so talking about deforestation, talking about public finance for those projects that are also going to improve biodiversity is a real positive. But overall, I don’t think anybody is popping the champagne quite yet.

Interviewer: Nick Petrić Howe

Yeah, and I think that cautious optimism is the feeling I’ve got from people on the ground as well. Like, some of the scientists have been saying, ‘I have to hope, like otherwise why am I here,’ but they do understand there is a long way to go.

Interviewee: Flora Graham

And once we get out of this kind of utopian bubble of the conference itself, there are a lot of very serious real-world decisions that are going to have to be made and, as Nature reporter Jeff Tollefson said the other day, it’s easy to make promises decades in the future. The question is what actions are you going to take in the very near-term future that are going to have a huge effect on people’s lives, huge effect on economies, both positive and negative, to actually achieve those goals. So, I think everybody has their fingers and toes and every appendage crossed, but really the scepticism is at a very healthy level.

Interviewer: Nick Petrić Howe

And even within this utopian bubble, there have been some caveats to some of the proceedings. For example, Russia and China have not had huge delegations.

Interviewee: Flora Graham

There’s no doubt that without the full engagement of these huge economies, we as a planet are going to struggle to achieve these goals. And of course, we don’t know necessarily what’s happening right now in the negotiation rooms, and this is really where the rubber is hitting the road, so you’ve got these big commitments made early in the week, very, very big headlines, but the devil is in the detail, and right now the unsung negotiators are really bashing out every word of these agreements. And we might find that when those actually come out, they might not back up some of the promises that seemed very hopeful early on. We might find that the words are there but the structures are not going to be in place to actually make those words a reality, so there are huge, huge question marks, and the absence of some of the major delegations is one of them. But even some of the huge delegations, I mean Brazil is one of the biggest delegations at the conference, and Brazil has done things like sign up for the pledge to stop deforestation, which is a very important pledge, one that we’ve heard before, one that has a very hopeful tone, but the actions of the Brazilian government have not recently been sufficient to achieve an end to deforestation, and in fact deforestation in Brazil has been accelerating. So, even with the delegations that are very much present, there can be a disconnect between the actions and the words.

Interviewer: Nick Petrić Howe

And I think I’ll be amiss to not mention as well things people have told me on the ground and things I’ve seen, is that this conference has an air of being slightly exclusive, with COVID and with the difficulties of coming into the UK and the cost of it, many people haven’t been able to attend who have in the past. Has this impacted how things have gone so far?

Interviewee: Flora Graham

I think there’s no doubt that COP has an equity problem, both on the ground in the conference. I mean, it was hard enough for us to get here from London. I can’t even imagine the multi-day processes that people have gone to get here from the South Pacific, for example, where they’re facing climate change in a very real way, or from Indigenous communities in South America. But it’s bigger than that. It’s the fact that a lot of the climate finance that was promised has not materialised for countries around the world and I know that we’re written in Nature that some of the original architects of the Paris climate agreement are really disappointed about how some of the richer countries have not backed up a lot of their funding promises, which really is what is going to drive equity as we reach a sustainable future. So, I think the equity problem here on the ground is something of a reflection of the issues that surround climate justice.

Interviewer: Nick Petrić Howe

Finally to wrap up, looking forward to the rest of the week, how do you think it’s going to go? Do you have any predictions for what’s going to come out of the last few days of the negotiations?

Interviewee: Flora Graham

Honestly, I think any predictions I make right now are probably coloured by my own hopes. Let’s be honest, at the end of the week we’re all going to go back to our regular lives, whatever those consist of, and we’re going to have to face the future with what comes out of this conference. So, I don’t predict that there is going to be any huge, revolutionary overturning where we’re going to suddenly have a wholesale remaking of our entire infrastructure. I feel that there’s going to be a long road ahead and we are not going to get any easy answers at the end of the week. But nevertheless, I think, as you said earlier, we have to hope otherwise what are we doing here?

Host: Benjamin Thompson

Flora Graham there, talking with Nick Petrić Howe. Head over to the show notes where you’ll find a link to all of Nature’s coverage of COP. And if you want to get stories from the final few days of the conference delivered straight to your inbox, make sure to sign up for the Nature Briefing, and you’ll find a link of where to do that in the show notes as well.

Host: Shamini Bundell

Not only that, but Nick, Flora and the rest of the team have also been busy finding scientists to answer some of your climate questions, and there’ll be links to some videos that they’ve made in the show notes.

Host: Benjamin Thompson

And that’s all for this week’s show. But before we leave you, don’t forget to follow us on Twitter – @NaturePodcast – and you can email us on podcast@nature.com. Until next time, I’ve been Benjamin Thompson.

Host: Shamini Bundell

And I’ve been Shamini Bundell. Thanks for listening.