Climate change slowing Earth's rotation, and hotels in space

Plus, a fascinating feat of animal memory
29 March 2024
Presented by Chris Smith
Production by Rhys James, Will Tingle.


A floating iceberg.


This week on The Naked Scientists: Check your watches: how climate change is making the Earth turn more slowly; we’ll also hear from the Cambridge scientists investigating whether vaccines can combat bovine TB; and would you be prepared to shell out millions for a luxury trip to space? One company is optimistically planning an orbiting space hotel for the years ahead.

In this episode

A floating iceberg.

Climate change is slowing Earth's rotation
Duncan Agnew, University of California, San Diego

The news is awash with the worsening effects of global climate change. But the stories reported are usually centred around the human and ecological side of the ongoing crisis. Now, however, a new study published in the journal Nature has suggested that the melting poles might cause a shift in our timekeeping too, by making Earth fatter around the middle. Duncan Agnew is from the University of California, San Diego…

Duncan - The leap second seems very peculiar. The problem is that the timescale that we all use is doing two things. It is matching atomic clocks, which tell very accurate time, and it is also trying to match the rotation of the Earth. And those don't give you exactly the same thing. A day on rotation of the Earth is not the same as a day from atomic clocks. And so just as if one clock runs slower than another, the difference adds up. The difference between these two measures of time adds up and every so often it gets to be as much as a second, which is a lot for some people. And then an additional second is added to a minute in order to bring the two times back into agreement.

Chris - Why does the world worry about such a tiny amount of time as a second every so often? Why does it matter?

Duncan - The difficulty with leap seconds is that all the computers in the world need to know about them or they're not synchronised. It's exactly the problem you have when you go to summertime and you've forgotten that everybody's gone to summertime and then you discover you're late to everything. Now a second doesn't sound like much, but for example, the standard for giving times of stock trades is a millisecond, a thousandth of a second. So that kind of very precise timing is actually very common. We just don't notice it.

Chris - And so if it goes off whack, we could end up with fraudulent transactions, errors in our transactions, people taking out money from ATMs when they didn't, and so on. So it would amount to a financial disaster and all kinds of problems.

Duncan - Right. And the financial system, I think, knows about this and deals with it well, but you never know what could go wrong somewhere else if somebody hasn't synchronised their computer and every time there's a leap second, some people don't do it when they should. Some people actually put a second in the wrong direction. There's plenty of scope for human error.

Chris - So your project started as a consideration of time and this concept of a leap second, but where did you take it next? Where was your thinking going?

Duncan - The reason for leap seconds, as I said, is the difference between atomic clocks and the time as viewed as the rotation of the earth goes around once a day. And so I came at this as a geophysicist who studies how the rate of Earth rotation varies. It does not change very much, but over time it changes a lot. In geologic time, hundreds of millions of years ago, the day was much shorter. There were 400 days in a year. Currently there are changes. They are small, but they're the thing that gives you leap seconds. So I looked at causes of changes in Earth rotation

Chris - And way back in history, then, why was the Earth spinning faster? Where has the energy gone?

Duncan - Basically, this is because of the tides. So the Moon and the Sun, gravitational attraction causes tides in the ocean. The simplest way to put it is that the motion of the water has some friction in it and exerts a frictional force on the solid Earth. And so it's like putting a brake on something. And so it's called tidal friction and it slows the Earth down. It's been slowing the Earth down since the earth had oceans. And over the long run, that's the biggest change in rotation.

Chris - But as anyone who's ever ridden a fairground ride knows, that also the rate at which something rotates is down to where you put the mass, the weights, on it. So will the redistribution of things like water around the Earth also have an impact? Because of course, that has changed over the time that the Earth's been around.

Duncan - Yes, that's exactly right. If you have something spinning and it changes shape, then it will spin faster or slower. The usual example, and there are plenty of YouTube videos of this, is ice skaters who start to spin, pull their legs and arms in and start spinning faster in the case of the Earth. What's been going on particularly recently is a lot of melting of ice in Greenland and Alaska. That ice flows into the ocean and is spread out over the entire Earth. And so effectively that's the opposite thing where the skater moves her arms out, the water has moved from near the pole too far away from the pole, and that's slowing the Earth down. So it's acting in the same direction as tidal friction.

Chris - How did you actually do this to be able to say to me what you just said?

Duncan - The way we know about this is partly from studies of melting ice and sea level, but this change of mass, of water moving from being frozen at the poles to all over the ocean, changes the Earth's gravitational field, and that's measured by satellites. That's been measured since 1976. And there was a long term trend in it that people understood. And starting around 1990, that trend slowed down and now it's reversed. So I used the gravitational field measurements from satellites as a way to get at what water distribution had occurred and how that would change rotation.

Chris - And how much of a difference is this making already and how much of a difference might it make if we see climate change play out the way that we think it will?

Duncan - The difference already is not large, it's now comparable to tidal friction. This didn't exist 30 years ago. The amount of slowing from tidal friction was what it was. It's still the same. In the meantime, ice melting is now slowing the Earth as much as tidal friction does, and we expect that to go up. Now, this is a relatively small change. It's not the catastrophic part of global warming. There are plenty of other things that are catastrophic about it, but it's a change we could see. And to me, one of the impressive results of this paper is the realisation that global warming is causing the entire Earth to slow down. It's not just some local effect that we could actually see in our very precise measurements, another sign of the fact that global warming is causing unprecedented things to happen.

A fresian cow

Bovine TB vaccine cuts spread through herds by 80%
Andrew Conlan, University of Cambridge

Bovine TB is a dairy farmer’s worst nightmare. Controlling the disease, which is very similar to the form of TB contracted by humans and can actually infect us too, involves rigorous screening, and culling of any animals found to be harbouring the bug. This approach to management, though, which is common across the EU and related countries, has made it very hard to gather adequate evidence about the potential effectiveness of the vaccine we have for TB and which might provide a superior way to control the condition. Now researchers at the University of Cambridge have managed to do the requisite trial, by working in Ethiopia. Vaccinating cows, they’ve found, doesn’t prevent infection, but it does dramatically reduce the severity of the disease in affected animals, and it cuts the rate of spread through herds by over 80%. The study’s author is Andrew Conlan…

Andrew - Tuberculosis in cattle is known to be associated with reductions in productivity. And what I mean by that is costs for farmers due to the animals producing less milk or having less quality meat. Historically, the risk to us from cattle has been from drinking unpasteurised milk. That was responsible for killing around 2000 children every year back in the 1920s before we brought in pasteurisation. And that risk is actually one of the main motivations for why we want to control bovine tuberculosis. Although as long as you pasteurise milk, actually that risk is probably quite small.

Chris - Farmers dread this arriving on their farm among their herd though, don't they? Is that because the control measures are quite draconian?

Andrew - Certainly in the UK the costs associated with the disease are almost entirely down to the costs associated with control. If a farmer gets TB on their herd, they have to go through a very punishing series of tests of every animal in their herd at regular intervals to demonstrate that the herd is clear from infection. And that's incredibly costly to farmers because of the animals that they lose, the time that they lose in doing the testing and the interruption to their business because they can't trade animals while they're under restrictions.

Chris - We do have vaccines that can combat tuberculosis. We used to give them routinely to children in the UK and other countries. We don't anymore. Are they any good?

Andrew - So the vaccine that we have for tuberculosis is the same vaccine that we've had for over a hundred years. But when it has been tried in the past using experimental challenges, where we actually artificially infect animals with tuberculosis, it has a very low protection. But the vaccine has been known for a long time to reduce the amount of disease in animals and the rate at which they become sick.

Chris - And is that what you set out to test here then to try and get some physical numbers around this?

Andrew - The argument for using this vaccine was always that, by reducing the rate of progression of the disease, it could also reduce the rate of transmission within herds. But that hadn't actually ever been measured before. And it was only by using a very clever natural transmission design where we compared the rate of transmission, actually measured it directly for animals that had been vaccinated and then infected and animals that had been not vaccinated and infected, that we could actually measure directly what this effect on transmission had. And what we found was that in terms of the rate of transmission or the protective effect on transmission, BCG is very good, has up to 80% reduction in transmission, compared to about a 20% reduction in terms of having lesions. Now it's important to remember those animals still have evidence of infection but are much less extensive, much less progressed and than animals that weren't vaccinated.

Chris - Where did you do this and how?

Andrew - So these studies were done by our colleagues at the Animal Health Institute in Ethiopia. There's a good reason for doing these studies in Ethiopia. So when we tried to do natural transmission studies in the UK, they were basically a failure because we didn't see enough transmission. And that's because in the UK, as soon as we find an animal that tests positive to TB, we kill it. In Ethiopia, which has endemically infected herds, there's already a supply of these animals and the facilities there allowed us to do these studies over a period of two to three years.

Chris - And you find that although animals pick the disease up, they don't develop this significant severe disease and they don't transmit it among themselves at anything like the pace they would've done if they weren't vaccinated.

Andrew - That's right. The fundamental readout of the experiment was that we compared animals that had been vaccinated and infected and those that had not been vaccinated put them in contact with fresh animals. And we saw that the animals that hadn't been vaccinated had pretty much the same rate of transmission as the animals that we recruited from the field. Those that had been vaccinated at a dramatically lower rate of transmission

Chris - Is the argument then that it's a good idea to vaccinate your cattle, but you accept that we will see infection, but we won't see anything like the rate of disease transmission through a herd.

Andrew - So bovine tuberculosis control is what we call a wicked problem. The biggest barrier to the use of vaccination has been that we know that it interferes with the current tests that we use to detect infection. So in countries like the UK where we actually have quite extensive control measures, vaccination could actually cause more problems if it undermines the action of the controls that we have. Because of this context, vaccination isn't currently recommended by international bodies. And that's a shame because actually in countries that don't have control measures at all at the moment, like Ethiopia with emerging dairy markets and increasing risk of transmission of bovine TB vaccinations could actually be a very cost effective way to reduce the risks and potentially increase the health of animals in those farms.


Unique memory 'barcode' allows bird to find stored food
Selmaan Chettih, Columbia University

Memory is a funny thing, and comes in various different forms. One is episodic memory, the ability to store information about unique experiences and when they occurred. This kind of memory is pivotal in animal species that squirrel away - and remember the location of - thousands of food items during the good times for when it’s much less plentiful. And now scientists from the University of Columbia have made a breakthrough in understanding how they manage this feat of memory. By monitoring the brain patterns of chickadees, small members of the tit family of birds, they saw that at the moment of making a cache, the brain’s hippocampus activated a unique assembly of neurons corresponding to each individual food store.  Selmaan Chettih explains…

Selmaan - It looked to us like when the bird made a cache, the hippocampus activity entered this different kind of state. It just looked really different than when the bird was just navigating around. And in this sort of different caching state, there were a couple things going on and the most interesting one was that there was kind of a unique pattern that happened for each cache. So each time the bird cached, you got sort of like a unique kind of label and this is what we were calling the barcode. It's a different pattern of activity that occurred for each cache.

Will - If these birds are going round and storing thousands, even hundreds of thousands, of caches per year, do they have a unique barcode for each one?

Selmaan - Yeah, that's exactly the thought. You know, like we're studying them in the lab, but the finding that they can generate these really unique labels like that was pretty new. We didn't expect that before we went in. And it really matches well with what we think these animals are doing in the wild because they have to keep track of so many different things and you don't want those different memories to interfere with each other or blur into one another.

Will - Yeah, that does sound like an immediate advantage for this memory system because if you do have thousands of individual caches to remember, you can't afford to blur those memories or else you starve.

Selmaan - Yes, exactly. Yeah. Or you might think, you cache a food item on the left and then you cache another food item on the right. Then if you blur them together, start thinking there's a food item somewhere in between those two. But you really have to keep all the memories separate and very precise. And we think that this barcode mechanism might be a way for them to do that.

Will - Do we know why this has become so distinct and separate from their regular navigational memory? Because I would've assumed that caching in this way requires knowing how to navigate to individual sites.

Selmaan - Yeah, that's a really interesting question. So another striking thing about these sort of barcode patterns is that they're a really transient thing that happened when the bird cached, which is like a second long. So it's like a quick blip almost in the signal that you have to know exactly when to look to see it. When we first started, that wasn't the framework we were going into the study with at all. There's been a lot of work on the hippocampus of many species for a long time showing these famously called 'place cells'. And these cells represent where an animal is. And the thinking was based on previous work that when the animal forms a memory, there'd be a change in place cells and that maybe you would have more place cells representing a location where you made a cache. We didn't really see that and it caused us to sort of look in a different direction. It's a really interesting question. I think it's kind of an ongoing question of research first, now. The speculation is that there's really a different kind of memory between remembering something that's kind of like a stable, like a feature of the environment. Like there's a lot of food here or in this place, this is like a scary sort of part of the environment or this is the regular path I take to work. That's a different kind of memory than like an individual event that just happens once and you kind of want to store that episode. And so we think that maybe the brain has different kinds of mechanisms for these different kinds of memory.

Will - When you say this episodic memory flashes for a short time, it almost feels like when you go to the shops and come home and see a gap in your fridge store and you think 'milk, I forgot to get milk.' It feels like the inverse of that, that enough contextual prompts kind of ignites short episodic memory for them.

Selmaan - Yeah, it's very much like that. We've kind of looked at them, they form the memory and their recall of the memory is like they're basically back at the site and they're about to retrieve that cache. But that's actually like something that we're really interested in looking forward to in the future. Sometimes you recall a memory like that, but sometimes, to use your metaphor, you're in the grocery store and you remember then, 'ah, I need milk.' And we actually haven't really shown yet if this barcode pattern is also underlying that kind of recall. So that's kind of like an ongoing project that we're working on now.

Will - Do we think this is unique to chickadees? Could this expand out into the wider animal world?

Selmaan - We certainly don't know the answer, but we think it could be more widespread. There's no evidence particularly that this would be really specific to chickadees. Caching is a really clear behaviour. It's really easy to identify when a memory is formed by looking at when a bird caches. Usually it's very hard to figure out exactly when an animal is forming a memory. So we think it just could have been hard to see in a lot of previous experiments. And actually there are a couple studies actually in humans that are sort of hinting at something similar. So we're excited about the idea that this could really generalise across organisms.

this is a picture of an astronaut doing a space walk

Hotels in orbit, and space headaches
David Whitehouse

Up into space now, and stories of orbiting hotels and spacefarers with headaches with the space scientist, author and former BBC science editor, Dr David Whitehouse…

Chris - I was intrigued to see that I could be going on holiday in space <laugh> not for long and only if I have about 40 or 50 million quid. But this is an American company that is saying a hotel coming to an orbit near us, in other words Earth orbit, imminently.

David - Yes and no. It's true the International Space Station is coming to the end of its life and it'll be replaced by a lot of smaller space stations built by smaller companies. But big companies like Boeing and Lockheed Martin will build these stations. And on the side of that, there are lots and lots of smaller companies who want to get in on the act. And this company is one of them. And what they're hoping to do is dazzle you with a dream of a hotel in space and a vacation in space that is more science fiction than reality, in the hope of attracting investors so they can get the things started. That's a well-worn technique to actually get space missions and space enterprises working is that you promise them not quite the Earth, but you promise them a hotel in space, knowing you can't deliver in a couple of years time. But if you get enough people enthusiastic with enough money, you can be on your way and start your journey to actually doing it perhaps a few years later. So hotels in space, yes, 10 years away perhaps, but if somebody tries to sell you a room in a hotel in the next couple of years, then look at the small print. We will eventually be able to buy hotels in space for the very rich. And there are a lot of very rich people who could sustain a market for this, but not yet. Not for you and me.

Chris - Reading the report of what above space has in mind suggests just getting there is about £40 million. Your 4-18 hour stay on their proposed station. They've got two in mind, Voyager and Pioneer. One of them actually has 400 rooms they say they're going to have in space, which effectively 'creates' gravity by spinning. I'm not sure what the experience will be like, but it certainly sounds like something not for the faint hearted at this stage.

David - And also the bank balance of above space is not exactly healthy. So you might want to think twice before you invest.

Chris - You might get marooned up there. The other thing that came out, there's a paper on astronauts and headaches. So let's hope that when you've spent your 40 million quid, you either take the paracetamol along or they've got some for you to take. What's this all about this, this point about people who are spacefarers suffering headaches?

David - Well, you know, when you go into space, there are all sorts of problems associated with zero gravity. Because zero gravity is not natural. We have not evolved in zero gravity and we can't live in zero gravity indefinitely. There are adaptation and serious problems in living in zero gravity of which headaches was the particular subject of this study. And they found that now when you go into space and you choose an astronaut, you are a fit person, the type of fitness that actually most people could achieve but few do. And they quite naturally don't suffer from headaches down here on the ground during training, but they do in space. I mean, only about 40% of them said in a survey over 10 years of going into space with the various astronauts, that they had headaches from time to time, but most of them, nine out of 10 said when they went into space, they had headaches. And that's an interesting reason for that. They think it might be due to pressure in the brain, which is serious and needs studying. We still have such a long way to go to understand how humans adapt to go into space. There's a funny story. The Americans used to say that the thing they used to get was sore hands. And why did you get sore hands? They said, because every time we went to touch anything, a Russian cosmonaut would slap us on the hand and say, 'don't touch' <laugh>. And you know, go and mop up the condensation. It's gone way beyond that. Going into space for long periods of time does serious things to your body, of which headaches are perhaps not the most important, but needs to be studied. And certainly, say, Scott Kelly, who was in space for well over a year. It's likely he's not back to normal now because he was in a terrible state when he came back. And there's an astronaut on the Space Station now called Gennady who, when he comes back later this year, will have spent over 1100 days in space on his various missions. He may never be totally back to normal because of the problems which he will bring with him, this industrial disease for astronauts. If we want to go to Mars in the future, we need experiments and studies like this and we need to know a lot more about how people react to being in space.

A sleeping infant

Why is a baby's grip so strong?

Thanks to Andrew Bremner for the answer!

Andrew - Infants are born with a really wide range of different reflexes, including the stepping reflex, the moro reflex, the suck reflex, and the rooting reflex alongside the Palmer implanter grasps. And traditionally, people have argued that reflexes at birth are automatic and governed entirely by the spinal cord, with no involvement at all from the cerebral cortex in the brain.

Will - And if the grip is a reflex instead of a conscious choice, it makes sense then for there to be less quality control involved. Anyone that's had their knee hit in that one place that makes you kick isn't really in control of how hard the kick is. And if the grip is a reflex, it makes sense for it to wane as the baby becomes a bit more cogent and aware of how the world works.

Andrew - As the cerebral cortex matures and starts to exert more of a controlling role on action via the spinal cord, it starts inhibiting the strong spinal reflexes observed at birth. Eventually, neonatal reflexes are largely overlain with, or replaced by, intentional and controlled actions. So rather than demonstrating a stepping reflex, then that gradually wanes and then is replaced of course by locomotion. So crawling and eventually walking in young children.

Will - But what do more recent studies say about this theory?

Andrew - The traditional explanation of this early strength of newborn reflexes has received a bit of critique more recently. So researchers have noticed that newborn babies can behave in what looks like a controlled rather than an automatic, reflexive way. Newborns can actually move their hand to intercept a moving object, which they've seen with their eyes. And some reflexes, far from being automatic, are actually strongly affected by the infant's current state. For instance, the rooting reflex, which is involved in feeding, occurs much more when newborn babies are hungry. I think there's probably a bit of truth in both of these perspectives, the more recent one and the traditional one. So newborn reflexes are likely not entirely automatic. So we know from neuroscience research that the cerebral cortex is functioning and plays a role in movement early in development. But perhaps this is a matter of degree and probably the inhibiting role of the brain in moderating strong and more automatic spinal reflexes is not fully developed yet at birth. So we don't have a cut and dry answer to the question of why newborn reflexes like the palmar grasp are so strong, but I suspect that it's because they're more automatic and less controlled than they are later in development.

Will - Perhaps a bit of both then. Thank you to Paris for the question, and to Andrew Bremner for the answer.


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