Podcast: Negative emissions and swarms under strain

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Host: Benjamin Thompson

Welcome back to the Nature Podcast. This week, we’ll be finding out how honey bee swarms keep it together under stress.

Host: Adam Levy

Plus, we’ll be learning the ethics of sucking carbon dioxide out the atmosphere. I’m Adam Levy.

Host: Benjamin Thompson

And I’m Benjamin Thompson.

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Host: Benjamin Thompson

Well listeners, before we start this week’s show, I’d like to interrupt our regularly scheduled programming with a little bit of news. This week’s podcast is Adam’s last for a while. He’s leaving us as co-host after, what, hundreds of episodes of the podcast?

Host: Adam Levy

Yeah, pretty much! I’ve been here almost exactly three and a half Earth orbits around the Sun. I first appeared on the show reading the Research Highlights way back on the 26th March 2015. I’ve learnt a huge amount in that time and it has been such a constant joy to discover new research and new ways of sharing it every single week. So, it’s with a heavy heart that I’m leaving the show and all its fantastic listeners.

Host: Benjamin Thompson

Well Adam, we’re very sad that you’re leaving as well. Listeners, stick around until the end of the show and we’ll let you know where you can follow Adam’s future endeavours. For now, though, Adam, what have you got for us this week?

Host: Adam Levy

Well, as regular listeners will know, climate change is the epicentre of my scientific obsessions. So, for my final week hosting the show, I wanted to bring you a final story about global warming. Now, to stop the world heating up we need to limit the amount of carbon dioxide in our atmosphere. The obvious way to do this is to stop pumping it up there in the first place. The quicker global emissions fall to zero, the lower the temperature rise we commit our planet to. But cutting emissions isn’t the only way to stop greenhouse gases building up. What if we could actually remove CO2 from the atmosphere? There are plenty of ideas for these ‘negative emissions technologies’. They range from the simple — planting trees, to the high-tech — building machines that actively suck CO2 from the air. But while the ideas themselves are still somewhat speculative, they’re actually built into our plans for the world’s climate future. In Paris in 2015, the world agreed to keep global warming to well under 2 degrees, with a goal of just 1.5 degrees. But the world has already warmed by 1 whole degree — just cutting emissions may not be enough. We may need negative emissions to reach even the less ambitious 2 degree target, and the scale may be huge. Here’s environmental scientist Jo House.

Interviewee: Jo House

The scale of greenhouse gas removal, these negative emissions, is really large. So, most of the global scenarios that were included in the most recent intergovernmental panel on climate change assessment indicate just to get to the 2 degrees target you need several hundred gigatonnes of carbon dioxide removal and I’ve seen figures that it’s equivalent to about 17 years’ worth of current emissions.

Interviewer: Adam Levy

Removing these levels of carbon dioxide poses serious challenges. Take one of the most commonly considered negative emissions approaches — bioenergy with carbon capture and storage or BECCS. BECCS would burn biomass for energy and then capture and store the CO2 before it entered the atmosphere. But the amount of land that certain scenarios suggest might be required for BECCS is truly vast.

Interviewee: Jo House

It can be from kind of zero amount of BECCS to about 700,000,000 hectares of BECCS in some of the scenarios, and to put that in context for your listeners, that’s about twice the size of India. So, some of these scenarios include massive areas of land use change.

Interviewer: Adam Levy

Changing land use on such scales would pose a huge technical hurdle. But in a Comment piece out this week, philosopher Dominic Lenzi suggests that there are other concerns that need careful consideration.

Interviewer: Dominic Lenzi

There’s a very real chance of conflicts with other land use goals, such as global food security, water and of course, biodiversity. So, there can be really sharp trade-offs created by this kind of negative emissions demand.

Interviewer: Adam Levy

Many negative emissions approaches raise important ethical questions about how we use vast amounts of land then. These ethical questions in turn raise difficult legal questions. That’s according to environmental lawyer Jonathan Church.

Interviewee: Jonathan Church

Issues of, you know, land rights and ensuring people aren’t exploited, people who live, you know, off the forests, and a lot of these ethical issues run into those issues of how to ensure that the law, particularly in the developing world, is robust enough to deal with a lot of the consequences that could come out of the expansion of negative emissions.

Interviewer: Adam Levy

The problem, Dominic argues in his Comment piece, is that these questions simply aren’t being asked. While negative emissions are an implicit part of many plans to limit global warming, he believes that their implications are not considered when it comes to crucial climate negotiations.

Interviewer: Dominic Lenzi

I would say that many policymakers would not be aware of the requirements of negative emissions. They certainly weren’t, it seems, during the Paris negotiations. It really throws into question the idea that we’re doing clear-sighted policymaking and policy assessment if we don’t really appreciate the ethical implications of what we’re talking about.

Interviewer: Adam Levy

And this isn’t just a problem for policymakers. Jonathan, who works at environmental NGO ClientEarth, feels that the law is also playing catch-up with these considerations. To some extent, he feels there just isn’t a full enough understanding of the potential risks and gains of different approaches. And for a scientist like Jo, bringing these considerations into the discussion on negative emissions would be a welcome development.

Interviewee: Jo House

And it’s essential to bring in the social sciences, philosophy and different, you know, groups of people because at the end of the day, models can look at maybe technology but actually, implementation and the effect that has will depend on these more socioeconomic aspects.

Interviewer: Adam Levy

However our societies weigh up these socioeconomic aspects, one thing is clear — negative emissions are no magic bullet allowing us to avoid cutting carbon dioxide emissions. Even with stringent cuts starting today, negative emissions may still be required to limit global warming. And if we don’t start cutting emissions soon, we may be faced with even starker choices.

Interviewer: Dominic Lenzi

The later we start to decarbonise our economies, the more negative emissions we’ll need and the more severe the likely risks are. The longer we wait, the worse the consequences will be and the sharper the trade-offs. And that’s really the point, that we should be starting now and thinking about negative emissions, not delaying and then thinking about negative emissions at 2050, say. Then we’re really limited to a set of scenarios that are all quite bad.

Interviewee: Jonathan Church

Negative emissions, I guess, are a way of bailing water out of the bathtub before it overflows. So, the main thing is you turn off those taps and we do that as fast as we can. I guess the analogy of bailing water out is a little too kind because we don’t know if these buckets hold water.

Interviewer: Adam Levy

That was Jonathan Church of ClientEarth, and before him, Dominic Lenzi of the Carter Research Institute in Germany, and Jo House who’s based at Bristol University in the UK. Find Dominic’s Comment piece at nature.com/news and for more on the technological side of greenhouse gas removal, Jo contributed to a recent Royal Society report on the topic. Find that at royalsociety.org.

Host: Benjamin Thompson

Coming up in the show, we’ll be learning about the super sensitive cameras capturing images deep sea creatures, and that’s in the News Chat. Before then, Anna Nagle is here with this week’s Research Highlights.

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Interviewer: Anna Nagle

What if we could put Europe on a diet? Not a crazy cabbage soup diet, just adhering to national healthy eating guidelines. It turns out this could drastically cut the amount of water used in the region. A team of scientists looked at the amount of water needed to produce the food and alcoholic drinks consumed in the UK, France and Germany. If people stuck to a balanced diet rich in grains, fruit and veg, the water footprint would fall by up to a third. The savings would be even bigger for pescatarian and vegetarian diets. The scientists hope their research could help policymakers manage increasingly scarce water resources, but it’s not easy to convince people to shift their eating habits. Check out the paper over at Nature Sustainability.

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Interviewer: Anna NagleThere may be a new crack in CRISPR Cas9’s capabilities. Hailed as a hugely powerful tool for editing DNA, new research suggests the system struggles when the DNA is all wound up. To tweak a genome, the Cas9 enzyme cuts DNA at a specific site. But many cells store their DNA by winding it round proteins, a structure called a nucleosome. Scientists found that in yeast, the CRISPR machinery worked much more efficiently when the nucleosomes weren’t present. But it struggled when the DNA was still wrapped around the proteins. The researchers say their findings could help scientists decide where to target their CRIPSR cuts and whether they need to remove the nucleosomes first. Read more in the Proceedings of the National Academy of Sciences.

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Host: Benjamin Thompson

Next up, reporter Noah Baker has been investigating how a swarm of bees hold themselves together.

Interviewee: Mahadevan

Any animals who live collectively have to solve problems on a scale which is much larger than individuals so, for example, when bees bivouac.

Interviewer: Noah BakerA bivouac is a temporary structure formed entirely of the bees’ own bodies. They form them when they’re moving to a new nest. You may have seen them hanging in trees — as you get closer you can see the bees clinging on to each other in a hanging, writhing swarm.

Interviewee: Mahadevan

I got interested initially just because I was fascinated by the shape of a bee cluster.

Interviewer: Noah Baker

That’s Mahadevan, a mathematician, physicist and biologist from Harvard University. He got interested in the mechanics of how a bee cluster holds itself together.

Interviewee: Mahadevan

It looks somewhat conical and then the actual question was why is it conical? A second actual question is does it remain conical always, for example, if it starts to get very cold, or you start shaking it?

Interviewer: Noah BakerBee clusters are often shaken about by the wind, or predators, or, very occasionally, by an elaborate piece of lab equipment designed by Jacob Peters and his colleagues.Interviewer: Jake Peters

I’m a honey bee researcher and I built this rig with the rest of the group to shake a swarm of honey bees. The honey bees were attached to a board which we moved back and forth with a motor and we filmed their response.

Interviewer: Noah Baker

Now, Jake didn’t attach the bees themselves. Instead, he attached a small cage containing their queen.

Interviewer: Jake Peters

And she gives off a particular pheromone that signals to the rest of the bees and they use aggregation behaviour to form a cluster around her.

Interviewer: Noah Baker

Then they wobbled the resulting cluster up and down and from side to side, and it was during the side to side wobbling that the researchers noticed something interesting. Mahadevan put me in the bees’ shoes to demonstrate what it was.

Interviewee: Mahadevan

If I ask you to imagine what would happen if I put you in an elevator, for example, and started shaking the elevator. What would you do immediately to try and stabilise yourself?

Interviewer: Noah Baker

I suppose flatten myself down.

Interviewee: Mahadevan

Exactly, so you want to start crouching because by crouching you reduce your centre of mass and by reducing your centre of mass you tend to become more stable, and so with this you do exactly what the bee would do, except they do it collectively.

Interviewer: Noah Baker

The swarm flattened out from what was a conical structure to something which better resembles a lumpy pancake. To find out a bit more about what was going on, Mahadevan turned to Orit Peleg, a computer scientist who has a bit of a knack for biological systems.

Interviewee: Orit PelegSo, the model was trying to take our experimental observations and try to use them to reverse engineer what bees are sensing locally inside the swarm. And the way to do that was basically to model the swarm as an elastic material, where we can measure the mechanical perturbation that each point in the swarm is experiencing and by doing that the strain gradient is increasing upwards as you get closer to the base.

Interviewer: Noah Baker

The bees at the base of the upside-down cone — the top to you and me — are holding up the weight of all of the bees underneath, so this is where the strain is highest. That strain is evened out a bit when the swarm evens out and that’s good for stability. But while the forces act on the whole swarm, it’s not actually a single entity. Here’s Mahadevan again.

Interviewee: Mahadevan

So, then you ask, well, how do they do it because it’s not an individual, it’s a collection. And so, we essentially traced our bee lines, so to speak. We can see that they essentially move. We can only see it from the outside because we didn’t use any fancy imaging to see what happen to the bees inside, but they gradually move from the tip of the cone, so to speak, towards the base of the cone.

Interviewer: Noah Baker

In Orit’s models, she could show that if every bee responded to the strain of shaking by moving towards the stress, the shape of the colony as a whole flattens out and becomes more stable. What’s also interesting is it seems that the bees don’t need to communicate with each other in order to undertake this communal flattening. Here’s Jake again.

Interviewer: Jake Peters

The real integration of information in the swarm is mediated by mechanical forcing rather than direct communication. Even in the absence of any form of explicit communication through pheromones or acute fixed signals, the bees can coordinate this shape change that we see in our experiments.

Interviewer: Noah Baker

And Orit suggested that a process like this could one day be applied to robot swarms.

Interviewee: Orit Peleg

In the last couple of years, people have been giving a lot of attention to swarm robotics and robotic materials which would potentially need to solve a similar problem to the problem that the bees need to solve, which is creating stable structures that respond to the environment and maintain mechanical stability. But I think this is still a bit futuristic for computer science and robotics, but the first step is maybe to learn something from natural systems that have had the privilege of evolution to perfect those structures and maybe take those principles and project them to robotic systems.

Host: Adam Levy

That was Orit Peleg from the University of Colorado, Boulder. Before her, you heard from Jacob Peters and Mahadevan who are both from Harvard University in the US. Read more on that story in Nature Physics: nature.com/nphys. And if you have to see it to bee-lieve it, then check out our YouTube video on the study: youtube.com/NatureVideoChannel for that.

Interviewer: Benjamin Thompson

Right listeners, our last segment for today is of course the News Chat, and I’m joined here in the studio by Jane Lee, one of the News Editors here at Nature. Hi Jane.

Interviewee: Jane Lee

Hello, good to be here.

Interviewer: Benjamin Thompson

Well, we’ve got two stories from research conferences today, and well, my goodness, they couldn’t be more different. For the first one, let’s head over to Barcelona, where the European Association of Archaeologists recently had a meeting, part of which focused on a section of society that’s been rather overlooked in the field of archaeology. Jane, I mean what can you tell us about it?

Interviewee: Jane Lee

Right. So, researchers are starting to pay a lot more attention to what children who were alive hundreds to thousands of years ago were doing with their time so what kind of work they were doing, and they’ve been finding some really interesting details.

Interviewer: Benjamin Thompson

I guess a lot of archaeology has looked at sort of child burial or diet, but this has been looking at sort of how they’re spending their day-to-day existence.

Interviewee: Jane Lee

Researchers knew that children were working; it’s not like that was a complete surprise or anything like that but what is interesting and is new is the sort of details of what these children were doing with their lives. So, you know, researchers are finding skeletal remains and even artefacts with, you know, little tiny fingerprints from kids as young as maybe six and you know, kind of suggesting that kids were making clay pots and stuff like that.

Interviewer: Benjamin Thompson

Yeah, and in the article on nature.com/news, I mean it says that some of these findings go back to well, thousands of years ago, right?

Interviewee: Jane Lee

Yeah, the Bronze Age. There’s a salt mine in Austria that researchers have been excavating for a while and in the Bronze Age section of the mine, they found a child-sized leather cap and some tiny little tools like picks and things, suggesting that kids were working down there about two centuries earlier than researchers previously thought.

Interviewer: Benjamin Thompson

Well Jane, the conference session that these results have been show at was called Children at Work. Do we know maybe why children have been potentially overlooked a little bit in the field of archaeology?

Interviewee: Jane Lee

Well, I think they’re one of several groups that have tended to be overlooked and it wasn’t until maybe about the 90s when more and more archaeologists started paying attention to what women were doing in the past. And some other researchers were like hang on, let’s look at these other groups and one of the overlooked groups was children. I think part of it may be just that there’s not as much evidence of kids and what they were doing as perhaps there is for the adults.

Interviewer: Benjamin Thompson

Well, you say some evidence was found in a mine and that seems like fairly backbreaking work. I mean what other things have been found that suggest what children were doing in antiquity?

Interviewee: Jane Lee

Right, so there’s a site in France actually, where a researcher found three baby teeth with these cylindrical grooves in them, and she says that that tends to form when someone uses their teeth to really stretch and work animal tendon or plant material for things like sewing or making baskets. And the teeth belonged to two children between the ages of 1 and 8, so those teeth are actually dated to between 2100 and 3500 BC which makes them among the oldest evidence for children engaged in skilled labour.

Interviewer: Benjamin Thompson

Well, I mean I have to say Jane, this is all kind of a little bit upsetting, you know. Are there any other examples where things maybe weren’t quite so terrible?

Interviewee: Jane Lee

Yeah, you know, there’s some evidence in Canada actually that a researcher has found, and he’s found evidence of children making these clay vessels and he says that in a lot of modern-day communities, you know, only pots of a certain quality make it to the kiln to be fired and perhaps used. But at his site he finds that even the kind of the wonky ones made by the little kids made it to the kiln to be fired, and you know, he says that it shows that the children in these societies had a certain level of social value because they were taking the time to fire the pots that these children were making.

Interviewer: Benjamin Thompson

Well Jane, finally on this one then, so I mean if this is kind of a growing field but maybe it’s been overlooked in the past, what happens next? Where’s it going?

Interviewee: Jane Lee

So, some of the researchers are actually going to go back and take a fresh look at some of these sites that people have been excavating for a while. So, the researchers looking at the salt mines in Austria, to kind of confirm that children may in fact have been working down in the Bronze Age section of the mine, they’re going to actually look at human piles of excrement in these sections, and they’re going to examine them for samples that actually lack sex hormones, which is indicative of younger children who just haven’t matured. So that’s one of the things that they’re looking at and one of the researchers, Mélie Le Roy, says that in the next years we will find more and more evidence that children were participating early in their lives in economic society.

Interviewer: Benjamin Thompson

Alright then Jane, well for our second story then let’s change tack and head deep into the oceans.

Interviewee: Jane Lee

Okay right, so we’re going to dive down thousands of metres with researchers who showed some really cool videos of animals at the Deep Sea Biology symposium in Monterey, California, and that was early in September.

Interviewer: Benjamin Thompson

Right, and so I imagine a lot of sort of submarines here and a lot of strange little jellyfish and what have you.

Interviewee: Jane Lee

Well, so these researchers were using remotely operated vehicles and, you know, with these really cool advances in cameras and low-light sensors, they’re able to see behaviours and light displays that just have eluded them for years.

Interviewer: Benjamin Thompson

Oh, so we’re sort of right down here where there’s no sunlight.

Interviewee: Jane Lee

Yes, it’s dark and usually when researchers go down this deep, you know, 1,000 metres down, they need to bring these really bright lights with them. It’s a bit like driving a Mack Truck down a really dark roadway. The animals that they encounter aren’t always at their best, shall we say. Some of them look a little stunned, kind of like, what’s happening?

Interviewer: Benjamin Thompson

I’d like to say rabbits in the headlights, but maybe in this case it’s maybe sort of deep sea fish in the headlights.

Interviewee: Jane Lee

Yeah, and so researchers have been trying to tweak the cameras and the sensors so that they can dim the lights and, you know, explore this realm in as natural a setting as they can.

Interviewer: Benjamin Thompson

Well don’t keep us in suspense then Jane, what sort of things have been found then?

Interviewee: Jane Lee

There’s this one animal called an arrow worm and it’s fairly well-known; it’s not like it’s a completely new animal to science. But these researchers were able to catch it actually giving off these little doughnut rings of pale blue light and it’s sort of like this vortex, this trail behind it, and that’s something that they hadn’t ever seen before and they were able to capture it with these really advanced cameras.

Interviewer: Benjamin Thompson

Wow, so we’re kind of seeing behaviours then that well, are new to science I guess.

Interviewee: Jane Lee

Yeah, and actually with other advances in the resolution, researchers are actually able to put 8K cameras on these underwater robots. So 8K camera resolution actually nearly matches that of the human eye and so researchers can take recordings of near-microscopic plankton with such resolution that they can identify them to species.

Interviewer: Benjamin Thompson

Well, people say that we know more about the surface of the moon than we do kind of the bottom of the ocean and what’s living there. What are researchers saying about how this technology is going to help move things forward?

Interviewee: Jane Lee

Well, you know, it’s bringing up more questions than answers, which in some ways is a good thing and one of the researchers was saying it’s taking them past the kind of ‘gee-whiz’ phase, you know, that it’s all really, really cool but, you know, what do these behaviours mean, how do they help the animal function in their habitat, things like that.

Interviewer: Benjamin Thompson

Well, Jane, thank you so much for joining us and listeners, what I’ll say is there’s some animated GIFs of some of these animals and you can see kind of the pulses of light coming from them, and you’ll find those over at nature.com/news. That’s also where you’ll find all the latest news from the world of science.

Host: Adam Levy

Well, that is it for this week’s show and that’s it from me.

Host: Benjamin Thompson

Yep, certainly the end of an era and listeners, I’m sure you will join me in thanking Adam for his amazing work on the podcast and I’m sure you’ll miss him just as much as we will. But Adam, where can listeners find out what you’ll be up to next?

Host: Adam Levy

Well, if you type in ClimateAdam — that’s all one word — into Twitter, YouTube or Facebook, you’ll track me down. It will surprise none of you, I’m sure, to know that I plan to continue to witter on about climate change and other science for quite some time.

Host: Benjamin Thompson

Nice one, Adam. I’m Benjamin Thompson.

Host: Adam Levy

And I’ve been Adam Levy. Thanks for listening.

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