This BBC podcast is supported by ads outside the UK. And international communication and streaming to return. Want to invest in big companies? Start for 1 euro per month and start today via Shopify.nl. hear how Sir David Attenborough has changed our world and inspired loads of you to take action on climate change. I'm Hannah Gelbart. You can listen on What in the World from the BBC World Service. Find us wherever you get your BBC podcasts. Hello and welcome to CrowdScience from the BBC World Service, the show that's powered by your curiosity. I'm Anand Chagatia and our question this week was sent to us from a beach in Australia. Hi there, it's Alison here from Sydney, Australia. Today I'm down at Cronulla, which is one of Sydney's southern beaches. It's a scorching hot day, the sky is blue, the surf is up and I'm just one of many people down here today taking a dip in the ocean to cool off. Recently I heard a report about oceans which said that nations in the Pacific are experiencing sea level rise at a faster rate than the global average. But to me that doesn't make sense. How can there be a global average? Surely all the oceans of the world are really just one big ocean So how can parts of it be rising faster than other parts? So there you go, CrowdScience. Can you please explain how it's possible for sea levels to be rising at different rates in different locations around the world? Thanks, Alison. I have to say I'm kind of stumped by your question. Surely you're right, and all the oceans are constantly sloshing into each other, so that any sea level rise in one part of the world soon balances out to the rest. To understand what's going on, first let's cover some basics. What's actually causing sea level rise? So there are two key factors that drive sea level rise, or let's say changes in sea level, because I mean sea level can go down as well as up. This is Jonathan Bamber, Professor of Earth Observation and Glaciology at the University of Bristol in the UK. So thermal expansion of the oceans. As they warm, they expand. And that's about half of present-day sea level rise. And the other half is due to changes in mass of the oceans. And that is almost entirely driven by melting of glaciers and the ice sheets that cover Greenland and Antarctica. And so how much of the world's water is actually locked up in the ice caps and in glaciers? so the ice sheet covering Antarctica in particular is huge I mean Antarctica itself is one and a half times the area of Australia it's a huge continent and it's almost entirely covered by ice and so if you take Antarctica and Greenland together that is somewhere around 80 percent of the entire freshwater supply of the planet is just locked up in those two ice sheets if you melted Antarctica and Greenland tomorrow, you would raise global sea level by about 65 metres. Whoa. I mean, that's a terrifying fact, but it just gives a sense of what all the water in the world is doing and I guess drives home how pressing and how sort of scary sea level changes are from climate change. That's the potential. Nobody is suggesting that those ice sheets are going to sort of dump all that ice into the oceans anytime soon. But if we look at in particular, the satellite record, we see a general increase in mass loss from both ice sheets. We'll be hearing more from Jonathan later. To answer Alison's question, we've travelled to a country in the Pacific, which is the part of the world that inspired her to get in touch. It's a place where sea levels are rising much faster than the global average, the island nation of the Philippines. Our first stop is a place called El Nido. It's a quiet tropical paradise famous for its coral reefs and pristine beaches. These are particularly beautiful with white sand, sapphire waters and lush green cliffs rising up along the coastline. So we've just driven to the beach in El Nido, the shoreline, and there are huge cliffs and mountains surrounding us and boats everywhere it kind of it feels like paradise really but for the people that living here it maybe isn't because just a few meters away from the shoreline there are lots of buildings houses you know hotels restaurants and the sea as we can see is is pretty close it's getting closer getting closer so right now we are looking for the changes because of climate changes, so we're going to go over there and ask the folks here about their already experience. This is our guide, Jordan. He's a park ranger, helping to manage and protect El Nido's incredible biodiversity. But today, he's helping us speak to locals who are directly affected by sea level rise. As we walk along the seafront, he points out some palm trees that show just how much the coastline is changing. It's not just that the water level here is increasing. Rising seas are also eroding the beach by washing away the sand. The sand has already been washed out by the ocean. I mean, these are massive, really tall coconut trees. They must be at least like 20, 30 metres tall. You can see how the roots of this tree, which we can see that the tendrils, they're just sticking out into the air. and before they would have been intertwined with all of the soil and there's loads of rocks and coral that they're sort of clumping together but now 50, 60 centimetres is exposed by the sea. Yeah, it's because of the changes of the ocean. These exposed tree roots, which would have previously been hidden underground, are a sign of how much the landscape here is shifting, something which residents have witnessed for themselves. Not far from the palm tree, a couple of small boats are beached on the sand. One of the owners is Rami Rodriguez, who runs boat tours of the surrounding islands. I have been here for 11 years and every day I see the water sea level changes. Now it's coming closer to our homes, just like last year. When it's low tide, the water goes further away from our homes, but when it's high tide, it comes closer here. Is the water reaching your house? Yes, there are months, like last December, the water reached our house. We used to live here, at this place, but we were told we need to move further away because the water is reaching our home. But there will come a time that we also need to move again because the water is coming really closer to our homes. So you've already had to move once and you might have to move again. Would you ever consider moving inland, away from the sea? Yes, we will have no choice but to relocate further, more inland, because we have no choice, because the water will really reach our homes. We walk further along the beach, past a couple of bars and houses, to a small beachfront massage parlour. Its owners Christy and Jenny are sheltering inside from the heat of the sun If the water comes here inside our business then we have no choice but to close the business because we have no other space to go We have no other place to build our structure our business So we might close if ever comes a time that water will enter our business. Do you worry about the future? Definitely, we are afraid. There's fear in us because we will lose our job not just for one day, for two days. it might be for months. Not only that we'll lose our jobs, but the things here, our equipments here will be damaged. So everything will be very difficult for us if ever water comes here inside our business. Visiting El Nido, I can see for myself how quickly sea level rise is happening and how much it's affecting the people who live here. But how fast exactly? And how does that compare to the rest of the Philippines and the rest of the world? To learn more, we make our way to the University of the Philippines in Manila to meet someone who can explain the science behind rising sea levels. I am Chorina Lin Repolo. I am an assistant professor and I am an expert on physical oceanography. But currently I'm also sitting or serving as the deputy director for research and development of the Marine Science Institute. The Philippines is a country with over 7,000 islands and a huge amount of coastline. does that mean that sea level rise is a particular worry for a country like the Philippines? Yeah, so sea level rise is very important because as an archipelago we have a lot of islands and that translates to a very long coastline. And most of our coastal communities live along these coastlines, low-lying coastal areas that really are significantly affected by even small changes in sea level. We've been traveling around the Philippines and we went to a place called El Nido and there the sea levels are rising. We spoke to local people about how it's affecting them. Do you have any figures for what the numbers are? So El Nido has a sea level rise of about 9mm per year and in comparison to Metro Manila which is about 13.13mm per year. And for a context, if you compare it to the global sea level, global sea level rise is about 3 to 4 millimetres per year. So those areas are experiencing like 3 to 4 times increase compared to the global sea level rise that we have. So it's not just that the Philippines is experiencing sea level rise well above the global average. Even within the Philippines, there's variation. The seas around Manila are rising even more quickly than those around El Nido. But how do oceanographers like Chirina actually measure that? Here in the Philippines, we started monitoring the sea level, but more for safety, for ports, for navigation and for shipping. That started in the early 1900s, but eventually because now we tend to experience and believe the reality that sea level change is here, and it's increasing as time goes by, tide gauges becomes one instrument that we use to monitor sea level rise. And what is a tide gauge? How does it work? So a tide gauge is like, you know, it's an instrument that you install near the water. So it measures the variability of sea level. So it has like, you know, a floater. And then once it moves up and down, it measures the height. And then you can have the sea level as time goes by. In El Nido, we spoke to some people who have buildings or businesses or homes on the seafront, and they have had to move their homes back a few meters away from the sea. And that's challenging enough, I think, dealing with people in a place like that. But in somewhere like Manila, which is a huge city with millions of residents and lots of buildings, that's going to be a huge challenge, right? Just moving further back into the land. There's no more space. There's no more space moving back. I think the best way to address is to adapt, move all your establishment away from the coastal areas. Manila is one of the world's largest and most densely populated cities, and it's very low-lying, with some areas only just above, or even below, sea level, which means that any increases are keenly felt by the millions of people who call this place home. Charina is keen to introduce us to a place that's doing work across the Philippines to protect people from the effects of climate change, the Oscar M. Lopez Centre. Hi, sir. Hi, Dr. Lascaux. I'm Anand. Anand, yeah. We've come to meet the centre's executive director, Dr. Radell Lascaux, a climate scientist and an author of several reports of the Intergovernmental Panel on Climate Change. He told us how their work is trying to help people in the country become more resilient to sea level change. A key to this is early warning. So we have beefed up our Met Office with newer equipment and more people, more training, more expertise, so we can predict ahead of time if a typhoon is coming, how strong, how much rainfall. And part of our effort is to model what's happening with our seas and the rising sea levels. And we translate these models into tools that people can use. We call it C-Narios. and this is a web-based tool and people can see what could happen to their cities when sea level rises and therefore see the the risk the vulnerabilities and the exposure that they will be subjected to with sea level rise. Thinking about the future is can be scary in the times that we live in even though we maybe have no choice but to face the reality that we're in I'm just wondering on a human level does this stuff keep you up at night? Well as a scientist who has been involved in all of this for maybe almost 30 years now. It's kind of half full, half empty glass for me. I've seen the change over the past 25, 30 years. People are more aware. But at the same time, the reality is we're not doing enough. The science is also very clear. We will breach 1.5 degrees centigrade, the Paris Agreement, and even 2 degrees, the higher limit, is probably going to be And so I think we need more political commitment by policymakers. We need more concerted global action. There is a window. It's fast closing, but still open if we do something now. But sadly, I don't see that kind of political commitment at the international level to really slow down the emissions of greenhouse gases. But we must not give up because change is possible. I have seen it. But at the same time, I am realistic enough to recognise that change may take time. But for the younger people who may be listening out there, don't give up. Keep on pushing and I think change could happen sooner than later. Listener Alison got in touch because she heard that sea levels are rising faster for Pacific countries than the world average. So far, we've learned how hotter temperatures are driving this change. We've seen that in Manila, sea levels are rising at almost four times the global rate, and that even across the Philippines, there's huge variation. But to tackle this question, we didn't just want to speak to scientists. We wanted to meet people who are living with the reality of rising oceans. And we'll be hearing more from them next. Shopify is the platform after millions of companies. With Shopify, you can simply create a professional website that fits your style. You can start hundreds of templates and start your own design studio in no time. Thanks to slim AI tools, you can write perfect text and you can see the photos of your products. And while you buy, you sell Shopify the rest. From the service and international processing, you will return. Will you grow? Start for 1 euro per month and start today via Shopify.nl. and discovering what the future holds for the Artemis space programme Just imagine what we as humans can do next. 13 Minutes presents Artemis II from the BBC World Service. Listen now, wherever you get your BBC podcasts. You're listening to CrowdScience from the BBC World Service, the show that rises to the challenge of answering your science questions week in, week out. I'm Anand Chagatia, and in this episode we're exploring how sea levels can be rising at different rates around the world. Surely the oceans all flow into each other, so there's only one sea level. Even though that sounds like a reasonable theory, we've seen it isn't the case. And in places like Manila, sea level rise is happening alarmingly quickly. To see the impact of this change for ourselves, we're heading across the city to a part of town near the waterfront called Parola Compound. It's an area with high levels of poverty, where recent floods have been particularly damaging. We're being accompanied there by a member of the Coast Guard, whose offices are nearby. As we wait for our escort, we take the chance to ask the Coast Guard staff if they felt the effects of sea level rise here. I am Commander James Barandino. I am the acting deputy chief of Coast Guard staff for Marine Environmental Protection. Actually, during rainy days, we're experiencing a lot of flooding and the floods are getting deeper and deeper. nowadays it's not the same as usual. And so you are noticing that sea level rise is affecting the coastlines. Is that changing the nature of the work that you do? Is that presenting new challenges or meaning that you have to respond in different ways? Nowadays we experience a lot of rescues during rainy days and flooding. Flooding in different areas. and we're not only rescuing in the seawater but also inland. We set off from the Coast Guard offices to Parola Compound. This part of Manila has always been prone to flooding but with climate change it's becoming more frequent and more severe. so we've just driven down towards the the shoreline in manila we've driven through the industrial port through some security gates we've been let through by the coast guard and lots of people with guns lots of the coast guard staff are having their lunch here but there are also some informal settlements of people who live right by the waterline and they're really being affected by rising sea levels because the tide often comes onto land anyway here and over the last few years that's getting a lot worse so hopefully we're going to be able to go and meet people who live here. We meet 44 year old Robert Gonyo who was born here and has felt the worsening impacts of sea level rise. How have you been affected by the sea level rises in the last five or ten years? During typhoons, water really rises here, but even there's no typhoon at night. When the water level rises, when it's high tide, it reaches our home. The water goes up to my knee inside our house. Does that cause a lot of damage to your house, to your property? Yes, my house has been damaged three times now and it's being washed away by the seawater. That sounds hard. Has it been difficult for you? It's really difficult because I still need to pay for the water and electricity bills and I'm just a tricycle driver here. So you grew up here, you've lived here for 44 years. Have you noticed the problem getting worse since you were a child? When you were a child, was the problem bad? When I was a kid, when there was typhoon, water really reaches our house. But what I've observed is that as I grew up, even if there's no typhoon or there's no heavy rain, water really rises through the years and really reaches our homes. Sea level rise is part of the grim reality of climate change for many people living in Manila. Even the Coast Guard have had to move offices here because of flooding. So how can the Philippines be facing faster sea level rises than the global average? Back at the University of the Philippines, Charina has an answer. So there are places where sea level is rising and some are falling. And it's because of the geographic setting of the Philippines. Philippines is highly tectonic, so our islands are moving. So if you have like a sinking land, then it will enhance the sea level rise. And if you have like uplifting islands, then it will like cancel out the sea level rise. So that's very important. Okay, so maybe a way to think about it is that even though possibly the oceans are flowing into each other, at any one piece of coastline, what's happening to the land itself is also going to change how the rising seas will balance out. Yes, that's why we don't rely much on the global average of the mean sea level rise. But what we recommend is to have like a local assessment because every locality have different response on the sea level rise. So does that mean that there could be some places where even though globally the seas are rising, actually in some places sea levels will be falling? Yes. So there are areas that we measured from tide gauges that are also falling because of that. We also have very urban areas wherein there's a lot of groundwater extraction, and that also contributes to the falling of the land, the vertical motion of the land that enhances the sea level rise. So if you extract a lot of groundwater, so you're removing water excessively from the land. And that way, because there's no more water underneath, so the land will tend to subside, going and falling from their original position. So there you go, Alison. Sea level rise isn't just about the sea. It's also about what's happening on land. In places where the land is sinking, sea level rise will be accentuated. This is especially true in places like Manila, where groundwater has been removed, which also causes the Earth to sink down. But is that the whole story? Do the oceans themselves also behave differently in different locations on Earth? Well, it turns out they do, as oceanographer Jonathan Bamber, who we heard from earlier, explains. One of the things that is important to distinguish is the difference between what's called relative sea level rise and absolute sea level rise. Now, relative sea level is if you're at the coast, it's the change in the water level with respect to the land. And that can change because of changes in land elevation, primarily actually land subsidence. As we extract groundwater, the land drops. And so you can have no change in the absolute sea level, you know, no thermal expansion, no increase in mass, and you can get a change in the relative sea level if the land is sinking. So that would appear like sea level is, or what it would be, sea level is going up at the coast simply because the land is going down. Okay, so that's one aspect of sea level rise, is talking about relative sea level change to land. And then is there a sort of way of just measuring just the sea level, just in an absolute sense as well. So that's the other way of framing the sea level problem, which we call absolute sea level. And that is typically measured by satellites. And that absolute sea level is literally just the change in volume of the oceans and the change in mass of the oceans with respect to some reference surface And what I mean by that that is some fixed artificial surface So it almost like you got a kind of virtual measuring ruler Imagine always sort of sticking a ruler that you might see at a swimming pool sort of in the middle of the ocean, and it's sort of fixed rather than it's on the land and the land is sort of going up and down and then giving you changes in a relative way. Exactly. What you have to think about with this ruler is that it's sort of fixed in a sense with respect to space, you know, with respect to the centre of gravity or centre of mass of the earth. So it doesn't move in a virtual sense in space. Whereas if you had a ruler that was at the coast, for example, like a tide gauge, which is exactly what a tide gauge is, it's going up and down because the land is going up and down at that site. Using this way of measuring sea level, which ignores the effect of land movement, reveals that the oceans are rising at different rates across the planet. And amazingly, part of the reason for that is gravity. If you melt ice over Greenland and Antarctica, which is what is happening right now, and you stick it in the oceans, you actually change the gravity field of the Earth. That is the strength of gravity at different locations on the surface of the Earth. The gravity field is a function of how much mass there is in any one place. So, for example, if you fly over Mount Everest, the strength of gravity increases because you've got this huge piece of rock there. It's exactly the same with ice. And when you melt that ice and you put it in the oceans, you're spreading that mass over the whole of the oceans. And so what happens is in Greenland, and this is what's happening right now, the gravity field gets a bit weaker because the amount of mass over Greenland is going down. And what that means is the sea level around Greenland is actually going down because of the change in gravity due to that effect. I understand what you're saying. So the gravity is caused by the amount of matter, right? But then how does gravity sort of affect the sea level in one place? Like why would sea levels be higher if there was like more matter in one place that was ice and now it's no longer there? Well, that's because in the absence of tides and other effects like ocean circulation and currents, the surface of the ocean follows the gravity field of the Earth. So it's not completely flat. It's following the undulations in the large scale variation in gravity of the Earth. And so if the gravity field over Greenland gets weaker as the ice melts, which is what happens, then the water is pulled towards Greenland a little bit less. You know, there's less gravitational pull. And as a consequence, it goes down because it's not being pulled towards the land. so strongly. That's interesting that you brought up tides there because we know that because the tides are caused by the gravity of the moon sort of pulling the sea towards it, we know that gravity, even though it feels like it should be a minuscule effect, we know that gravity can have a meaningful effect on the way that oceans move. And so you're basically saying that if you had a big lump of matter, it's sort of pulling water towards it and therefore the sea level is going to be a bit higher. And then if you get rid of that matter, then that effect is no longer there and then the sea level is going to drop a little bit. Exactly. And superimposed on that gravitational signal is the signal due to thermal expansion of the oceans. And that varies globally, because it depends on how much heat is being absorbed by the oceans in any one location. And that heat is then transported towards the poles by major ocean currents like the Gulf Stream or the North Atlantic Drift. and those currents are transporting large amounts of heat they might be a little bit warmer than the surrounding ocean and therefore they're a little bit less dense and they're actually slightly higher than the surrounding colder water and so you get these variations due to different amounts of thermal expansion in the oceans ah okay so that's a second effect yeah that okay that makes sense as well. So basically, when things get warmer, they expand. So there's more actual energy from the sun going into the water there. And then in the same way as when you run a bath, and you have to sort of mix up the hot and the cold, that doesn't happen instantly, because as the earth is so big, so the warmer water isn't evenly distributed, and the energy from the sun isn't evenly distributed. So you get differences in the expansion. Exactly right. So to bring it back to our listener Alison's question, then, what's going to be the biggest factor? And does that vary in different countries? It totally depends on where you are on the planet. So in the tropics and somewhere like the Philippines, a big factor is land subsidence. But also in the Pacific, you have this thermal expansion component, which is much bigger than the global mean. And therefore, it's a kind of really amplified problem and a major problem for these small island states like the Marshall Islands and these Pacific atolls, which are only one to two meters above sea level currently and so are really seriously threatened by the amplified sea level rise you see there. You go to other parts of the planet, like the Southern Ocean that surrounds Antarctica, and the thermal expansion component there is below the global mean, so you're not seeing sea level rise rates as high as you are in other areas. So Alison, to answer your question, the way that our oceans respond to climate change is surprisingly complicated. You might think of the seas like a giant bathtub that fills up evenly if you turn on the taps. But in reality, water isn't uniformly distributed across the planet. Instead, it's being smushed around the Earth by differences in gravity and temperature. So, in an absolute sense, the seas are rising more in some places than others. Separately to that, the way that change is felt in a given place is also affected by land movement, which can exacerbate or counteract what's happening in the ocean. But whatever the root cause, as we've heard throughout this show, the impact of sea level rise is just as devastating. I'll give the last word to Charina in Manila, who told me how she feels about the future, given how quickly the seas are rising there. I think personally, you know, it's so sad that, of course, if you already have, like, house near the front beach and you want to relocate away from it, It's like it's hard to let go of it. But climate change is real. It's here. It's happening. So to protect life and to protect yourself, you just have to adapt. I think that's the best way moving forward. Adapt and respond to the existing reality of climate change. Thanks, Jirina. And thanks, Alison, for getting in touch. Over to you for the credits. you've been listening to crowd science from the bbc world service the question was from me alison at cronulla beach here in sydney australia the producer was dan welsh and the presenter was anand jagatia if you have a science question you'd like the answer to then please email it to crowd science at bbc.co.uk. Thanks for listening. The crew of NASA's Artemis II mission have returned home safely after successfully completing their groundbreaking voyage around the moon. Splashdown confirmed. Humans are back in the business of going to the moon. But while the mission is over, the Artemis space program is just getting started. 13 Minutes, the BBC Space podcast, is looking back on their epic journey and discovering what the future holds for the Artemis space program. Just imagine what we as humans can do next. 13 Minutes presents Artemis II from the BBC World Service. Listen now, wherever you get your BBC podcasts. ¶¶
