Heating of the Tasman sea warms up the climate of Antarctic Peninsula via changes in wind patterns, new study by Japanese and Australian scientists shows
The Antarctic Peninsula is melting faster than ever. In a recent study, scientists have revealed how heating in the Tasman sea causes warming of the West Antarctic region and leads to melting of ice and rise in sea levels. They suggest that wind streams flowing towards poles from the tropics play an important role in these oceanic and temperature variations. These findings can be helpful to populations that are vulnerable to sea level rise.
The melting of the Earth’s ice cover intensified in the 20th century, with glaciers and sea ice in the Arctic and Antarctic regions melting at alarming speeds. In fact, The Antarctic Peninsula (AP), which is the only landmass of Antarctica extending out past the Antarctic Circle, was found to be one of the most rapidly warming regions on the planet during the second half of the 20th century. This rapid change in climate has raised serious concerns of rising sea levels the world over.
Multiple factors have been associated with the melting of the ice cover: the primary factor being the greenhouse gas emissions from human activities that cause warming up of the atmosphere and the oceans and the consequent ice melting. Apart from this, atmospheric variations, ocean currents, and wind patterns also play a significant role. Now, a collaborative group of scientists from Japan and Australia—led by Assistant Professor Kazutoshi Sato from Kitami Institute of Technology and Associate Professor Jun Inoue from the National Institute of Polar Research in Japan—has focused efforts on understanding how fluctuations in these climatic factors affect the warming of the Antarctic. They have documented their findings in a brand-new article published in Nature Communications.
Previous studies have examined the relationship between the wind dynamics over the Southern Ocean (also called SO; located north of Antarctica) and climate variability in tropical oceans. It was found that heating in tropical regions generates atmospheric waves called “Rossby wave trains” from the tropics to the Antarctic region via the SO, which causes heating of the West Antarctic region. Interestingly, Rossby waves are an attempt of nature to balance heat in the atmosphere as they transfer heat from the tropics to the poles and cold air towards the tropics.
On the path of understanding the warming of AP, Dr. Sato points out, “The impacts of climate variabilities over the mid-latitudes of the Southern Hemisphere on this Antarctic warming have yet to be quantified”. His team addressed this gap by looking at the climate changes in the Tasman Sea located between Australia and New Zealand and the SO and drew correlations with temperature variations in the AP.
Dr. Sato and his team analyzed the temperature data from six stations in AP and the wind and cyclone patterns over the Tasman sea and the SO from 1979 to 2019. They found that even without unusual heating in the tropics, only the heating in the Tasman Sea modifies the wind patterns over the SO and forces the Rossby waves to move even deeper into the Amundsen sea low, a low-pressure area lying to the west of the AP. This larger pressure gradient causes stronger colder winds towards the poles. The meandering wind stream moves towards the AP, resulting in the warming of this region. Additionally, this effect was found to be prominent in the winter months when the cyclones are more active. “We have shown that warm winter episodes in the Tasman Sea influence warm temperature anomalies over key regions of West Antarctica, including the AP, through a poleward shift of South Pacific cyclone tracks”, Dr. Sato summarizes.
The ever-increasing warming of the AP—rather, the whole of Antarctica at large—is a major concern plaguing climatologists all over the world. Commenting on the serious implications of this rapid rise in temperature and sea levels and the importance of the findings of their study, Dr. Inoue says, “Antarctic warming accelerates Antarctic ice sheet melting and contributes to the rise in sea levels across the world. Therefore, knowledge of the mechanisms of the melting of the Antarctic ice sheet would help scientists, policymakers, and administrations to devise measures for people who will be most affected by the rising sea levels.”
Dr. Sato and his team conclude by stating that the findings of their study can also aid the future forecast of ice sheet melting in Antarctica and the consequent global sea level rise.
This is a transcript of episode 5 of The Conversation Weekly podcast, How climate change if flooding the Arctic Ocean with light. In this episode, two experts explain how melting ice in the far north is bringing more light to the Arctic Ocean and what this means for the species that live there. And we hear from a team of archaeologists on their new research in Tanzania’s Olduvai Gorge that found evidence of just how adaptable early humans were to the changing environment.
NOTE: Transcripts may contain errors. Please check the corresponding audio before quoting in print.
Dan Merino: Hello and welcome back. From The Conversation, I’m Dan Merino in San Francisco.
Gemma Ware: And I’m Gemma Ware in London and you’re listening to The Conversation Weekly, the world explained by experts.
Dan: In this episode, two Arctic Ocean researchers explain how melting ice in the far north leads to more light in the Arctic – and what that means for sea life.
Karen Filbee-Dexter: Our ecosystems are responding, because these changes are really dramatic and they’re noticeable.
Gemma: And we talk to a team of archaeologists about the early humans who lived in Tanzania’s Olduvai Gorge 2 million years ago.
Makarius Peter Itambu: In this scenario, hominims from Oldupa maintained the very same toolkit.
Dan: So Gemma, today we’re going on a journey up to just about as far north as we can go, all the way up to the Arctic. What do you imagine when I say the word Arctic?
Gemma: I feel a bit cold already, and I guess I think of big expanses of snow and ice, drifting, like wind. Maybe the odd polar bear. And I guess in winter it’s just dark.
Dan: That’s a great example if you were to stay on top of the ice, but there’s a whole different world beneath it. And it’s full of ocean, like teeming alive.
Gemma: We know climate change is causing some of this ice to melt though, right?
Dan: Yeah totally… well some of the ice melts every summer. The sun’s up and then in winter when the sun goes away it grows back, but that ice is melting much more than it used to. So in September 2020, Arctic sea ice covered 3.74 million square kilometres.
Gemma: Well that sounds like a lot…
Dan: It does. But it’s the second smallest measurement ever. And only roughly half of what was measured in 1980.
Gemma: So what does that melting sea ice mean for all that teeming sea life living in the Arctic Ocean?
Dan: It’s not clear cut… it’s not all bad news even. Different scientists are studying all sorts of changes to see how it’s going to matter for the life in the Arctic, but one of the things they’re looking at is light. If there’s less and less sea ice, more light gets down into the ocean. And in the dark winter, where ice would normally cover the ice caps, it’s not there, so ships are driving through more and more and bringing with them a lot of artificial light.
I spoke to two researchers who’ve been spending a lot of time in the cold icy waters way up north to study all of this. And let’s just let one of them kind of set the scene. So Gemma, and all you listeners out there, imagine you step off a plane in the far, far north. Here’s what you might see.
Karen: So you have these places that are so covered in snow and ice, that they almost have a moon landscape of just bare rock in the summer. No leaves, no forest, no trees.
Dan: That’s Karen Filbee-Dexter, a research fellow at the university of Western Australia and a scientist at the Institute of Marine Research in Norway. She’s talking about the shoreline there. The long dark winters make it so that even in the sunny summer, the landscape is barren. But in the ocean, there’s a very a different story.
Karen: And then you go under water and you have to go a little bit deeper, but when you dive you sort of past this zone, where all of a sudden these amazing underwater forests appear.
Dan: These forests are not made of trees of course, but of kelp, attached to the sea floor, swaying in the currents.
Karen: So you have these long blades that will float in the water column and then they, just like a forest, shade light and create these understory conditions that fish and animals use and live in the same way as a forest does on land.
Dan: And how big are we talking? And I’m thinking Redwood trees, or am I thinking a bush in my yard kind of size?
Karen: It depends on the species and it depends on the forest. So, the first kelp forest that I dove on in the Arctic was about one to two meters tall. And it was actually in Arctic Norway. But the largest kelp forest that I’ve been in the Arctic has been in Canada. So there is an area in Nunavut where the kelp was about three to five meters tall. And that was spectacular.
Dan: Until recently, not too much was known about Arctic kelp. What kind grow where, or even how much there is.
Karen and her colleagues at the Arctic Kelp project, an aptly named group of universities, institutions and NGOs across Canada, are trying to catalogue which kelps are growing in the Arctic today, and how the warming temperatures are going to affect where they grow in the future.
Karen has spent a lot of time underwater using scuba gear to study these kelp ecosystems. But for many of these places, you can only access them in the short window when sea ice disappears.
Karen: So that’s what’s incredible about these habitats. They’re covered by ice. For sometimes more than half of the year and they require light to live. So they’re just growing based on light that reaches the sea floor in this very short period when the ice is not there.
Dan: Kelps, and well, everything in the Arctic Ocean, spend a huge amount of time in the dark, either because it’s winter the sun hasn’t come up for months, or because the sea surface is covered by ice. When the ice melts and daylight returns, kelps grow really fast. They have to, it’s a short growing season. But that growing season is getting longer.
Karen: What’s happening now in the Arctic is we have this massive and dramatic loss of sea ice. So this means that a large amount of Arctic coastline, which is normally covered in ice and normally doesn’t get that much light is now suddenly sort of open to, to the sun.
Dan: All you gardeners out there will know this equation: more sunlight, more growth. As Arctic temperatures warm due to climate change and sea shrinks, these underwater forests are expanding, and kelp is now growing in places where it didn’t used to.
Karen: So based on, how the conditions have changed from 1950 to now, we can predict that the migration rate in the Arctic is about, 20km per decade. So this sort of poleward expansion is definitely marching along, and there’s all the evidence that these changes are accelerating.
Daniel: 20km per decade is pretty fast for a bunch of trees
Karen: Yes, the marching forest. It is definitely something out of a Lord of the Rings movie. But the rules are different in the Arctic, right? So, so it’s changing much faster than the rest of the world. Everything happening there is happening at, you know, two to three times the rate of change. So, we’re already way into the climate change future, along our Arctic coastlines. So it’s not surprising that our ecosystems are responding because these changes are really dramatic and they’re noticeable. And they’re going to put a lot of pressure on marine species to move.
Dan: These changes which are causing kelp to expand and move are not good everywhere though. A lot of the Arctic coastline is made of permafrost.
Karen: This is essentially frozen soil. When that frozen soil thaws all of that dirt and sediment just flushes into the coastal zone and creates a lot of turbidity.
Dan: This murky brown water prevents light from reaching the seafloor and the kelps growing there.
Another side effect of climate change is that glaciers and ice sheets are melting and dumping huge amounts of fresh water into coastal areas, that can also harm kelp.
So while not every change is good for kelps and seaweeds way up north, overall Karen says that predictive models show the future is looking pretty good for Arctic kelp forests.
In many other parts of the world, these ecosystems are shrinking, so it’s kind of cool that, as least to some extent, these losses are being offset up north. And a large expansion of underwater kelps might actually help slow climate change ever so slightly.
Just like trees on land, kelps rely on carbon dioxide to grow. Expanding kelp forests in the Arctic could become a pretty significant carbon sink. When these kelps die, they just drift slowly to the deep dark depths of the ocean, and because it’s so cold, they don’t really rot either. Instead, they just sit there, keeping corbon dioxide locked up at the bottom of the ocean.
There are other more tangible benefits to larger kelp forests too. It’s great habitat for marine life.
Karen: They’re going to have a higher canopy height and a higher biomass. This means that there’s more space for animals to live in. So basically more rooms in the house, more structure, more niches for different species to occupy.
It also probably will mean a shift in species. So most seaweeds and most kelps in the Arctic were almost kicked out in the last ice age and then they’ve been slowly inching their way back in. And some of them have done a better job and have adapted to these really extreme conditions, better than others.
Dan: Kelps aren’t the only thing that likes less sea ice. Us humans do as well. As sea ice decreases in both summer and winter, the formerly dark polar night that last for weeks or months, is now being lit up like never before by boats and the artificial light they bring in with them. This is a big deal to the multitudes of sea creatures that have adapted over millions of years to the darkness of the polar winter. One group of scientists is studying how this new influx of light is changing the behaviour of these animals.
Jørgen Berge: My name is Jørgen Berge, I’m a professor in marine biology at UIT, the Arctic University of Norway.
Dan: Jørgen, unlike most people, doesn’t actually mind the long dark, polar, winter. I spoke to him late last year, when the polar night in Norway had just begun
Jørgen: We actually just started the polar night items sitting now in Tromsø at 70 degrees north. The sun orbits around our horizon for 24 hours a day for two months in a row. There is still clear difference between day and night. But that difference becomes less and less the further north you get. And then once you get up to around 80 degrees, then the human eye is hardly able to distinguish any difference between night and day during the darkest part of the polar night.
But the polar night is certainly not just dark. It’s actually all about different kinds of light. Both background illumination from the sun, the aurora borealis the moon, also biological light.
Dan: Up until fairly recently, scientists used to think that the darkness of the polar night was uninteresting, devoid of life. But a research project that Jørgen started back in 2006 changed all that – and kind of by accident. His team was actually looking at how retreating sea ice would affect the marine ecosystem in an Arctic Fjord.
Jørgen: So we had to be there in the late autumn to deploy instruments that would then be in place and do measurements when the sun came back. But then as more or less a byproduct, the instruments were also doing measurements during the dark polar night. But when we got these data back, we started to realise that, hang on something, something is actually happening here.
Dan: What him and his team found changed scientists’ understanding of the polar night. The polar night isn’t not boring, far from it in fact.
Jørgen: So it’s a system that is in fact in full operation. Seabirds, fishes, zooplankton. It’s just so fascinatingly full of life during the, during the dark polar night.
Dan: One of the processes Jørgen and his colleagues has studied is called diel vertical migration.
Jørgen: That is the behaviour where organisms – zooplankton and fish – they move up from the deep up into the shallow, during nighttime and go migrate down into the deep, during daytime.
Dan: This is entirely controlled by light, so researchers just assumed it would stop. The polar night is just perpetual darkness after all.
Jørgen: It turns out that it doesn’t stop, it’s ongoing. One of the things that we have started to realise is how extremely intimately, these organisms are connected to the light climate, to ambient light.
Dan: Even with the sun gone during the winter months, light plays a huge role in the Arctic. The sun still brightens the sky ever so slightly as the earth rotates. Moon cycles also change light levels, and so does the aurora borealis. And creatures react to all of this. But when Jørgen and his colleagues were studying these creatures, they got conflicting data between the instruments they left alone over one winter and the data they collected from their boats. The reason was light pollution from the researchers themselves.
Jørgen: The first year we really didn’t fully really understand why the samples we took never matched the data that we got from acoustic instruments that had been deployed autonomously. But it turns out that these organisms, they are able to respond to extreme small levels of light.
Dan: Jørgen and his team need, well, light to work on their boat, so they use headlamps and floodlights and stuff. For ultra light-sensitive sea creatures, these lights are huge signals. Some swim towards them, some swim violently away. And not just animals near the surface. The team found this happening down to depths of 200 metres below the sea level.
The effect of light pollution could be happening on a large scale, thanks to melting sea ice and increased human presence.
Jørgen: As sea ice retreats, as we start fishing further north, oil and gas exploration, shipping, not the least, more and more human presence in the high Arctic during the polar night, then we also bring with us artificial lights. At the moment we are not able to, to, to say to which degree this really is a problem, but, that is one of the things that we are now really starting to look into.
Dan: And melting sea ice, well that’s climate change.
Jørgen: So artificial light, it’s not of course a direct effect of climate change, but it’s certainly related to climate change because as it gets warmer, as there is less sea ice then we see more human presence and human presence will, it means there’s more artificial lights involved.
Dan: So what does this all mean for the fish, zooplankton and other sea creatures that are super-sensitive to light and live in this high Arctic environment? Jørgen says that’s a difficult question to answer.
Jørgen: Personally, I think that we have to look at the effects in two ways. One is the direct effect of light pollution. It does affect organisms there and then. Most likely that effect is limited, because it only last while there is artificial light there. And there’s certainly a limit to the, the geographical extent of that impact.
However, I think there’s another effect that is much more important. And that is how it’s affecting our knowledge about the polar night. To take one example, there’s more and more fisheries the high Arctic during the polar night. If you want to do surveys to give an estimate about how much there is of say haddock or cod, you have to do acoustic surveys with research vessels in the polar night, in where we are fishing. And these measurements might be strongly biased and impaired.
Dan: Essentially what Jørgen is saying is that every measure of arctic fisheries even taken in winter could be way off. By bringing in light, the fishermen and researchers change how fish and other animals behave. This is one of the oldest problems in biology: how to study ecosystems without disturbing them. And I asked him he feels as a scientist, to discover that his own presence could be distorting the results of his research.
Jørgen: Yeah, it sorta makes you feel unwanted. You know, that your presence is affecting the organisms, but it also, as a scientist, it also makes me, maybe wonder and questions. And I find it fascinating trying to understand things I cannot see.
It’s difficult to explain, but to me, when you really go, go up into the high Arctic and you allow yourself to be in the darkness and you start to take in all the senses, the sounds, the light, it’s just a, just a miracle sometimes.
I can still remember one on the experience we had. This was one of the first years when we were up on Svalbard in, early January, and I was out in a small boat out in the middle of the fjord and we turned off the engines. We turned off all lights because we wanted to look for seabirds. And we looked down and we saw this upside down sky filled with blue-green light, and that was just an amazing experience to see all this organisms from big jellies to small unicellular organisms blinking and glowing and moving in all directions. That was a beautiful sight.
Dan: What Jørgen saw was bio-luminescence – light produced by creatures in the Arctic night to communicate with each other. When you live in total darkness, light is, almost paradoxically, one of the most important and useful things there could possibly be. Even to the scientists who study it, the darkness of the polar night is so much more complex than anyone even imagined.
Gemma: I love the idea of the ocean blinking back at you, that’s just so beautiful as Jørgen said.
Dan: It made me want to take a vacation to the polar night in the middle of winter, which I’d never thought I’d say before. But, it is also dangerous, both Karen and Jørgen were talking about polar bears and how you actually have to carry guns, so it’s not all blinky lights and gorgeousness.
Dan: Both Karen and Jørgen have written for The Conversation as part of a series we’re running called Oceans 21. It examines the history and future of the world’s oceans. On The Conversation’s website, we’ve actually got a profile of every ocean on earth and Jørgen and Karen contributed to the one on the Arctic.
Dan: We’ve put a link to that, and the Oceans 21 series, in the show notes.
Gemma: Coming up, a group of archaeologists talk to us about some of their recent finds from Tanzania. But first, we’ve got a message with some recommended reading from Laura Hood, politics editor and assistant editor at The Conversation in London.
Laura Hood: Hello. My name is Laura Hood. I’m a politics editor for The Conversation here in London. I’ve got two recommendations this week. I worked with a team of psychologists led by Daniel Jolley from the University of Northumbria here in the UK. He told me about some work his team has been doing investigating how young people are being affected by conspiracy theories in the pandemic. Before they got in touch. I hadn’t realised that almost everything we know about conspiracy theories is based on work investigating adults. We know next to nothing about how children encounter and absorb misinformation. So they’ve been conducting surveys with British adolescents to try to work out at what age we’re most vulnerable to conspiracy theories and the extent to which young people are being exposed to them during lockdown. It’s really interesting reading, I think, particularly for parents.
I’d also like to recommend an article written by Mark Toshner, he’s an expert in respiratory medicine at the University of Cambridge. He’s put together a guide for anyone who’s feeling a bit overwhelmed by the scientific information that’s flying around about vaccines right now. He says, he feels really sorry for us trying to absorb all this information and he wants to make it a bit easier. So he’s tackling topics such as what it means when we hear that one vaccine is 90% effective, say, or another one is only 70% effective. Is that something we should be worrying about? Should we be trying to pick and choose our vaccines? He’s also talking about what it means for a vaccine to be potentially less effective against particular types of variant of COVID-19. So it’s useful information at this stage of the pandemic.
Daniel: That was Laura Hood from The Conversation in London.
Gemma: So for our next story, we’re heading to a warmer climate, thankfully, to Tanzania in East Africa and a place called the Olduvai Gorge. It’s known as the birthplace of humanity.
Dan: Birthplace, so how long we talking here?
Gemma: Ages, so about 2 million years or so. And today, archeologists from around the world, come to Olduvai to study the remains of different species of early humans. But scientists are also interested in the ancient environment and what the gorge actually looked like back then.
Dan: So is there a name for studying ancient climates?
Gemma: Yes, and it’s a great one. It’s paleoecology. So basically this is looking for evidence of ancient plants and pollen, and even bits of airborne charcoal by delicately sifting through layers of sediment. So we’ve been talking to a group of researchers who’ve been doing this work in a specific parts of the Olduvai Gorge called Ewass Oldupa, which actually means “the way to the gorge” in the Maa language of the local Masaai and what they’ve found has provided new insights into just how adaptable early humans were to the changing environment around them.
Julio Mercader: I’m Julio Mercader and I’m a professor with the University of Calgary, which is in Western Canada.
Gemma: OK, and we’re talking to you today, Julio, about your most recent research that’s just been published. It’s about an area in Tanzania, in East Africa. Can you just give me a bit of context? Why is this part of the world so important for our history?
Julio: Olduvai Gorge is in East Africa, and if you think of it as a region – there is this reef that is splitting the crust of the earth that is allowing volcanoes to spit out lava and ash. But at the same time as the splitting, it’s making the terrain sink. And when that happens, you have water building up that forms lakes and rivers and swamps. And because of that biodiversity tends to be really, really high because nature is a really productive in these kind of a rfit context.
Now in East Africa, which is where Olduvai is, the rift has been alive, so to speak, for more than 20 million years so that when humanity is forming, several million years ago, early humans, like any other animal, are being attracted to the resources that you find in the rift.
Now life near volcanoes was preserved because the eruptions and the sediments covered that up and then archaeologists exposed it. So now imagine an African Pompeii. But this time is much older. It is two million years. And instead of Romans, you want to imagine humans. But these humans are not like you and I, huh? They are early humans, several species. Unlike today when there is only one species. And among them on Olduvai Gorge, you have the first member of our genus, that we say in biology, and that is the genus homo. Right? And so to sum it up, Olduvai Gorge is important because many aspects of early human life have been buried, covered and preserved for posterity. And it’s not only the human fossils, but what we humans did on a daily basis, our activities.
And as you know, the gorge is like a canyon, it’s like a small version of the Grand Canyon. And because there is like a scar in the terrain, you can see the fossils in the remains, popping out from the walls that create the canyon.
Gemma: So it seems like an incredibly important place for archaeologists like you and your colleagues. How long ago are we talking and is this a period of time when different species are actually competing for dominance?
Julio: Well, there is a lot we don’t know about this, but what we do know is that it was 2 million years ago. And at this point, what you have is humans belonging with a several genera. So for example, various homo habilis, and that species belongs with the same genus as you and I. But there is also paranthropus boisei, and other members of the australopithecines.
Now, are they competing directly with one another? From an ecological point of view, maybe not. Maybe not because we know that the adaptations, the morphology of the body, the cranial architecture, the diets may be a little different. So to explain this, imagine different species taking on different niches within the environment.
Gemma: OK, so let’s get into a bit more detail now about the research that you and your colleagues have recently published a paper on. What did you find?
Julio: We uncovered evidence that hominins were coming to a specific location within the gorge, which is on the western side of it. And, they kept coming back.
Gemma: To understand more about what the team of archaeologists found in the gorge, I spoke to two of the Tanzanians who’d worked on the study. Pastory Bushozi and Makarius Peter Itambu. I got them on a slightly dodgy line. So bear with us.
Pastory Bushozi: My name is Pastory Bushozi. I’m a senior lecturer at the University of Dar es Salaam, and archaeologist working on paleoanthropology.
Makarius: My name is Makarius, I’m a lecturer in archaeology, teaching human evolution, paleoenvironment and African stone age.
Gemma: What did you find? What did the ecology of the Olduvai gorge look like when these populations you were studying were living there 2 million years ago?
Makarius: The discovery revealed that the oldest Olduvai hominins used diverse but rapidly changing environments, that range from fern meadows, to woodland mosaics, but also natural band landscape to the lakeside. But also there’s woodland and palm groves, as well as steppes. Those were the kind of environment that looked like during 2 million years ago.
Gemma: So the landscape was changing, you were having forest, you having like a big steppe, you were having grasslands.
Makarius: Right, but the more interesting things, hominims continued to utilise the same toolkit, which is Olduwan. And this is so interesting because we believed that climatic change always trigger technological change, but in this scenario, hominins from Oldupa, it was the Oldupa site, maintain the very same toolkit, the Olduwan stone tools.
Gemma: You were seeing that they were using the same tools throughout that period?
Makarius: Yeah, that was so fascinating that despite of these rapid changes, adaptation to this major geomorphic and ecological transformation did not have any impact.
Gemma: Here’s Julio Mercader again.
Julio: What is interesting here is that over the course of 300,000 years, these Olduwan hominins are coming back to exploit different environments. And so what we have here for the first time is evidence in one place of the diversity of the adaptive tools and strategies that humanity is using to exploit many different ecologies and environments, showing an early example of great adaptability
Gemma: So you were seeing a real ability to use the environment to their benefit?
Julio: That is right. And so to me, this is a real landmark because there is technological dependence, but also the ability to adapt to whatever changes there are happening. And so, in a way it is like the very beginnings of the invasive behaviour typifies any other pioneer.
Gemma: Dr. Bushozi, can I bring you in there. I understand it was you who made one of the oldest discoveries?
Pastory: Yes, it was me, because actually I found those stone tools that were coming on the lower sequence. So I was excited, myself, and I called my colleague to come and see that. That day, everybody was excited. So by then we were collecting everything to see what we were going to do in the lab.
Gemma: And are you able to do research at the moment or is the pandemic stopping your research in the gorge?
Pastory: Because of the pandemic, we are not doing research, but still we are working on the lab. The work I’m doing now is to clean those stone tools by using chemicals so that I can get a good picture on those stone tools, and then after that we are also trying to do get what kind of raw materials, what kind of implement they were using to shape those tools. And then when we go back into the field, we’ll be able to find, trace now where those rocks were coming from.
Gemma: Thank you so much for your time, I really appreciate it.
Makarius and Pastory: Thank you so much.
Gemma: You can read more about the research in a piece that Julio Mercader wrote for The Conversation about their findings.
Alright, that’s it for this week. Thanks to all the academics who’ve spoken to us for this episode – and to The Conversation editors Natasha Joseph, Jack Marley, Hannah Hoag and Laura Hood.
Dan: You can find links to all the expert analysis we’ve mentioned in the episode – and tonnes of other recommended reading – in the show notes. And if you learnt loads and want to read more, click the link to sign up for our free daily email.
Gemma: This episode is co-produced by Mend Mariwany and me, with sound design by Eloise Stevens.
Dan: Our theme music is by Neeta Sarl. Final thanks also to Alice Mason, Stephen Khan and Imriel Morgan.
Gemma: Thanks for listening everybody. Until next time.
The Gulf Stream is growing feebler, the Arctic seas are gaining fresh water. Together they could affect the world’s weather.
LONDON, 2 March, 2021 − The Atlantic Conveyer, otherwise the Gulf Stream − that great flow of surface water pouring northwards that overturns in the Arctic and heads south again at great depth − is now weaker than at any point in the last 1,000 years, European scientists report.
Scientists call it the Atlantic Meridional Overturning Circulation or just AMOC. Europeans know it as the Gulf Stream: the current that conveys tropic warmth to their coasts and keeps Britain and Western Europe at a temperature several degrees higher than latitude alone might dictate.
And for years, oceanographers and climate scientists have been observing a slowing of the flow, by as much as 15%. But direct measurement of the great current began only relatively recently in 2004: researchers needed to know whether the slowdown was part of a natural cycle, or a consequence of climate change driven by global heating.
Now they know a little more. European researchers report in Nature Geoscience that they looked for evidence of ocean circulation shifts in what they call “proxy evidence”: the story of climate change told by tree growth rings, ice cores, ocean sediments, corals and historical records, including naval logbooks.
The combined evidence of temperature patterns, the sizes of particles of ocean floor sediment and the salinity and density of sub-surface water helps build up a picture of the Atlantic current for the last 1,600 years.
“The Gulf Stream System moves nearly 20 million cubic meters of water per second, almost a hundred times the Amazon flow”
The verdict? Up to the 19th century, ocean currents were stable. The flow is now more sluggish than at any time in the last millennium.
This is roughly what climate models have predicted: the warm salty water moves north, cools, becomes more dense, sinks to the deep and flows back south. But the Arctic has begun to warm, Greenland to melt, and the flow of fresh water into the northern seas to intensify.
Since the flow is driven by the difference in temperatures, any change in the regional thermometer will play back into the rate of flow. And any extra arrival of fresh water could further slow the overturning circulation.
“The Gulf Stream system works like a giant conveyor belt, carrying warm surface water from the equator up north, and sending cold, low-salinity deep water back down south. It moves nearly 20 million cubic meters of water per second, almost a hundred times the Amazon flow,” said Stefan Rahmstorf, of the Potsdam Institute for Climate Impact Research, in Germany, one of the authors.
“For the first time, we have combined a range of previous studies and found they provide a consistent picture of the AMOC evolution over the past 1600 years. The study results suggest that it has been relatively stable until the late 19th century.
“With the end of the Little Ice Age in about 1850, the ocean currents began to decline, with a second, more drastic decline following since the mid-20th century.”
The change could have ominous consequences for European weather systems: it could also deliver more intense coastal flooding to the US eastern seaboard. If the current continues to weaken, the consequences could be catastrophic.
Which is why a new study in Nature Communications matters so much. US researchers tracked the flow of fresh water from the Beaufort Sea − melt water from glaciers, rivers and disappearing Arctic sea ice − through the Canadian Archipelago and into the Labrador Sea.
Arctic water is fresher than Atlantic water, and richer in nutrients. But this extra volume, measured at a total of 23,300 cubic kilometres, could also affect the rate of flow of the overturning circulation. That is because relatively fresh water is less dense than saline water, and tends to float on top.
Quite what role it could play is uncertain: the message is that, sooner or later, it will escape into the North Atlantic. Then the world will find out.
“People have already spent a lot of time studying why the Beaufort Sea fresh water has gotten so high in the past few decades,” said Jiaxu Zhang, of the Los Alamos National Laboratory, first author. “But they rarely care where the freshwater goes, and we think that’s a much more important problem.” − Climate News Network
Do migrants willingly choose to flee their homes, or is migration the only option available?
There is no clear, one-size-fits-all explanation for a decision to migrate — a choice that will be made today by many people worldwide, and by an ever-rising number in years to come due to a lack of access to water, climate disasters, a health crisis, and other problems.
Data is scarce on the multiple causes, or “push factors”, limiting our understanding of migration. What we can say, though, is that context is everything.
United Nations University researchers and others far beyond have been looking for direct and indirect links between migration and the water crisis, which has different faces — unsafe water in many places, and chronic flooding or drought in other places.
The challenge is separating those push factors from the social, economic, and political conditions that contribute to the multi-dimensional realities of vulnerable migrant populations — all of them simply striving for dignity, safety, stability, and sustainably in their lives.
A new report, Water and Migration: A Global Overview, from the UNU Institute for Water, Environment, and Health, offers insights into water and migration interlinkages, and suggests how to tackle existing gaps and needs.
The report’s information can be understood easily by stakeholders and proposes ideas for better informed migration-related policymaking. This includes a three-dimensional framework applicable by scholars and planners at multiple scales and in various settings.
The report also describes some discomforting patterns and trends, among them:
By 2050, a combination of water and climate-driven problems and conflicts will force 1 billion people to migrate, not by choice, but as their only option.
Links to the climate change and water crises are becoming more evident in a dominant trend — rural-urban migration.
There is a severe lack of quantitative information and understanding regarding direct, and indirect, water and climate-related drivers of migration, limiting effective management options at local, national, regional, and global scales.
Global agreements, institutions, and policies on migration are concerned mostly with response mechanisms; a balanced approach that addresses water, climate, and other environmental drivers of migration is needed.
Unregulated migration can lead to rapid, unplanned, and unsustainable settlements and urbanisation, causing pressure on water demand and increasing the health risks and burdens for migrants, as well as hosting states and communities.
Migration should be formally recognised as an adaptation strategy for water and climate crises; while it is viewed as a “problem”, in fact it forms part of a “solution”.
Migration reflects the systemic inequalities and social justice issues pertaining to water rights and climate change adaptation; lack of access to water, bad water quality, and a lack of support for those impacted by extreme water-related situations constitute barriers to a sustainable future for humankind.
Case studies in the report provide concrete examples of the migration consequences in water- and climate-troubled situations, including:
the shrinking of Lake Chad in Africa, and the Aral Sea in Central Asia;
the saga of Honduran refugees;
the rapid urbanisation of the Nile Delta; and
the plight of island nations facing both rising seas and more frequent, more intense extreme weather events; in addition, the added health burdens imposed on people and communities by water pollution and contamination create vicious cycles of poverty, inequality, and forced mobility
While the Sustainable Development Goals (SDGs) do not include an explicit migration target, mitigation of migration should be considered in the context of SDGs that aim to strengthen capacities related to water, gender, climate, and institutions. These issues resonate even as the world deals with the COVID-19 pandemic.
Recent news stories have chronicled the plight of desperate migrant workers trapped in the COVID-19 crisis in India, and of displaced people in refugee camps where social distancing is unachievable, as is access to soap and water, the most basic preventive measure against the disease.
Add to that the stigma, discrimination, and xenophobia endured by migrants that continue to rise during the pandemic.
Even at this moment, with the world fixated on the pandemic, we cannot afford to put migration’s long-term causes on the back burner.
While the cost of responses may cause concerns, the cost of no decisions will certainly surpass that. There may be no clear, simple solution but having up-to-date evidence and data will surely help.
Let us also acknowledge that water and climate-related disasters, ecological degradation, and other environmental burdens cause economic, health, and well-being disparities for migrants and populations living in vulnerable settings.
And the pay-off of silt-laden rivers and rising sea levels could be catastrophic floods, as swollen rivers suddenly change course. Since many of the world’s greatest cities are built on river estuaries, lives and economies will be at risk.
Three new studies in two journals deliver a sharp reminder that the consequences of global heating are not straightforward: the world responds to change in unpredictable ways.
“Although we anticipated the ice sheets would lose increasing amounts of ice in response to the warming of the oceans and the atmosphere, the rate at which they are melting has accelerated faster than we could have imagined,” said Tom Slater of the University of Leeds, in the UK, who led the research.
“The melting is overtaking the climate models we use to guide us, and we are in danger of being unprepared for the risks posed by sea level rise.”
The latest reading of glacial melt rates suggests that the risk of storm surges for many of the world’s greatest cities will double by the close of the century. But coastal cities – and the farmers who already work 38% of the terrestrial surface to feed almost 8bn people – have another more immediate problem.
In a warmer world, more water evaporates. In a warmer atmosphere, the capacity of the air to hold moisture also increases, so along with more intense droughts, heavier rainfall is on the way for much of the world. And the heavier the rain, or the more prolonged the drought, the higher the risk of soil erosion.
In 2015 the world’s farmers and foresters watched 43 billion tonnes of topsoil wash away from hillsides or blow away from tilled land and into the sea. By 2070, this burden of silt swept away by water or blown by wind will have risen by between 30% and 66%: probably more than 28 bn tons of additional loss.
This could only impoverish the farmland, according to a study by Swiss scientists in the Proceedings of the National Academy of Sciences. It could also impoverish people, communities and countries. The worst hit could be in the less developed nations of the tropics and subtropics.
But the flow of ever-higher silt levels into ever-rising seas also raises a new hazard: hydrologists call it river avulsion. It’s a simple and natural process. As conditions change, so rivers will naturally change their flow to spill over new floodplains and extend coastal lands.
Survival in question
But river avulsions can also be helped along by rising sea levels. Since 10% of humanity is crowded into rich, fertile delta lands, and since some of the deadliest floods in human history – two in China in 1887 and 1931 claimed six million lives – have been caused by river avulsions, the question becomes a matter of life and death.
US scientists report, also in the Proceedings of the National Academy of Sciences, that rising sea levels alone could make abrupt river avulsion more probable, especially as delta lands could be subsiding, because of groundwater and other extraction.
The dangers of avulsion are affected by the rate of sediment deposit in the river channels, and this is likely to rise with sea levels. This in turn raises the level of the river and eventually a breach of a levee or other flood defence will force the river to find a swifter, steeper path to the sea.
“They are sudden and sometimes catastrophic natural events that occur with statistical regularity, shifting the direction of major rivers. We are trying to understand where and when the next avulsions will occur.” – Climate News Network
By Zahra Kalantari, Davood Moshir Panahi, Georgia Destouni
Salt storms are an emerging threat for millions of people in north-western Iran, thanks to the catastrophe of Lake Urmia. Once one of the world’s largest salt lakes, and still the country’s largest lake, Urmia is now barely a tenth of its former size.
As the waters recede, extensive salt marshes are left exposed to the wind. These storms are getting saltier and are now happening more often – even in the cold and rainy seasons of the year. As more drying uncovers more salt marshes, things will only get worse.
Salt storms pose a direct threat to the respiratory health and eyesight of at least 4 million people living in both rural and urban areas around Lake Urmia. Increasing soil salinity reduces the yield of agricultural and orchard crops grown around the lake, while the lake has shrunk so much that boating is no longer possible, resulting in a loss of tourism.
This dramatic decline is down to human activity. Over the past three decades, Iran has followed a succession of five-year economic development plans, part of which involved providing large government loans for the agricultural sector to expand and switch from being primarily rain-fed to irrigated. To provide the necessary water for the farms, as well as for growing domestic and industrial use, more than 50 dams were constructed on rivers that drain much of north-western Iran and flow into the lake.
While these dams siphoned off the water that once fed the lake, the drying process was intensified by climate change. The rate of rainfall has reduced in recent decades and the Urmia basin has experienced several multi-year droughts.
All this has left a massively shrunken lake and a host of associated economic, social and health impacts. Yet what’s happening with Lake Urmia is just one example of water-environmental problems emerging right across Iran.
Iran is getting warmer and drier
In a recent journal article, we examined how both climate change and human activity had affected hydrological changes in Iran in recent decades. The country has 30 main river basins, and we gathered three decades of key hydro-climatic data for each, including surface temperature, precipitation, how much water was stored underground in soil and rock, surface runoff (the amount of excess rainwater that cannot be absorbed by the soil), and measures of evaporation and transpiration from plants.
We then calculated the average values of each of these variables over two 15-year periods, 1986-2001 and 2002-2016, and compared the two. This allowed us to see what was changing in each of these basins and by how much.
Our work showed that Iran’s main river basins have got warmer but are receiving less precipitation, are storing less water underground, and seeing less runoff.
Some river basins where precipitation and runoff decreased still saw an increase in evapotranspiration (the sum of evaporation and plant transpiration). This may seem odd at first, as less rainwater surely means there is less water to evaporate or for plants to transpire. Lake Urmia, for instance, is an endorheic basin, which means nothing flows out of it and all water that flows in eventually evaporates (this is why the lake is salty). But why would evapotranspiration have actually increased, even as the basin is fed by less water?
This is actually an indicator of human activity. First, all those dams generally increase the surface area of the body of water, compared to the natural flow before the dam was built. Artificial lakes and reservoirs, therefore, leave more water exposed to air and direct sunlight, thus increasing evaporation.
But it’s also down to farming. As more crops are grown, more water is transpired by plants – and more water is needed to grow those plants. To add water where needed, farmers have turned to groundwater and large-scale water transfer engineering projects.
This use of water to maintain and expand human activities is unsustainable and has serious environmental and socio-economic consequences, particularly in this dry part of the world, as seen by changes to Lake Urmia. Policymakers need to mitigate the adverse hydrological changes and associated socio-economic, environmental and health impacts, and move towards something more sustainable.
Modernizing flood forecasting and warning often comes with the requirements of knowledge transfer and expertise enhancement for forecasters, decision makers, and the residents in local communities. To ensure that the Flood Forecasting and Warning System that is being built for Hoi An city and VGTB Basin — a major catchment in Viet Nam—is able to operate effectively, an extensive collaborative modelling and training programme was held from July 2019 to February 2020, with support from the Urban Climate Change Resilience Trust Fund (UCCRTF).
The on-the-job training program was held in Tam Ky, Quang Nam, the mid-central province of Vietnam under ADB Grant 0462-VIE: Urban Environment and Climate Change Adaptation Project. Key deliverables of the project are:
a Flood Forecasting and Warning System (FFWS);
supporting the Provincial Hydrological and Meteorological Centre;
a Decision Support System (DSS); and,
supporting the Provincial Steering Committee for Disaster Prevention, Search and Rescue (PSCDPSR).
The project, underway since March 2018, is led by a consortium of Deltares (Netherlands), HaskoningDHV Nederland B.V. (Netherlands), SUEZ Consulting (SAFEGE) (France) and the Institute for Water Resources Planning (Vietnam). The FFWS and DSS for the Vu Gia-Thu Bon river system, was considered to be one of the most urgent (non-structural) project measures. The FFWS system is designed to improve the procedures for flood warning and timely evacuation, while the DSS enables the analysis of both structural and non-structural measures regarding flood management, and the study of water shortage problems and salinity intrusion during dry periods.
The project applied a state-of-art flood early warning system, called “Delft FEWS” – an open, flexible, free-of-charge software package developed by Deltares, to the Vu Gia Thu Bon river basin. This was paired with an upgraded MIKE river basin modelling package and a new Delft3D marine model to create an integrated FFWS.
Training to ensure long term sustainability
The goal of the training is to ensure the long-term sustainability of the FFWS, by building the capabilities of system developers and operators. A collaborative approach was deployed through a series of technical on-the-job training sessions, allowing participants to gain knowledge and know how to operate and maintain the FFWS and DSS in the future. The specific objective of the technical working and training sessions was to train the staff in using the calibrated models and operate the FFWS and DSS, and to teach them the process of building, calibrating and maintaining the systems.
One participant, Mr. Truong Xuan Ty, Chief of Standing Office of the Provincial Steering Committee for Disaster Prevention, Search and Rescue, said “we currently don’t use any forecasting software. If we can better understand the flood forecasting and flood warning models, by using the FFWS+DSS, this will greatly improve the efficiency of the decision making and will speed up the warnings to the communities”.
A total of nine training sessions were delivered to end users such as the Provincial Hydro-Met Centre (PHMC), the Mid-Central Regional Hydro-Met Centre (RHMC) and the Provincial Steering Committee for Disaster Prevention, Search & Rescue (PSCDPSR). The training was divided into two main components: (i) Catchment and river model development and (ii) Delft-FEWS flood early warning system configuration and operation.
The on-the-job training was organized at the end users’ location in Tam Ky city, Quang Nam province. Priority was given to the group of potential operators: forecasters from PHMC and RHMC and technical officers from PSCDPSR, by delivering intensive instructions and knowledge ensuring as much interaction as possible between trainers and trainees. Characteristics of the training sessions included:
Each technical session introduced a specific topic providing expertise on applicable tools, software, features, required data, know-how to self-configure and operate the models through various practical exercises.
Demo versions pre-configured for the project were provided for demonstration and practice during and after each session.
The demo versions were updated to reflect comments and requests from end users during and after each session. Agile work plans for the following sessions were arranged together with the end-users at the end of each session, to incorporate the user needs as much as possible.
The training was designed and lead international consultants. Because most local officers are not fluent in English, language barriers were a considerable challenge. To overcome this, a Vietnamese user interface was developed for both software systems and the training was delivered in Vietnamese by local trainers.
With the final training session held in February this year, a recap of the complete training was done with lots of room for interaction, by means of a Q&A session and a variety of user-selected practical exercises, such as the Delft-FEWS basic configuration and river catchment model set-up. The fact that most exercises were completed with little or no support from the trainers proved that the local skills on modelling, flood forecasting and warning had significantly improved through the concept of “learning by doing”.
For further information about the project and the training, please contact the authors: Bas Stengs (Bas.Stengs@deltares.nl) or Trang Dinh (Trang.Dinh@deltares.nl).
The pioneering infrastructure project to upgrade Washington DC’s combined sewer system used green infrastructure to reduce capital cost and build resilience to future flood risk. DC Water, the District of Colombia’s Water and Sewer Authority, adapted the $2.6 billion-dollar project to incorporate $100 million dollars of green infrastructure.
A new case study, produced by Acclimatise for The Resilience Shift, tells the story of DC Water’s journey to incorporate green infrastructure into such a large and important critical infrastructure project. From inventing the world’s first Environmental Impact Bond to finance the project, to delivering a jobs programme that allowed DC residents to maintain the green infrastructure, the Clean Rivers Project innovated at each stage of the development process.
DC Water, embarked on the Clean Rivers Project to managing combined sewer overflow events by implementing green infrastructure above ground, alongside grey infrastructure below ground, to help control the volume of water reaching the storm water drainage system. Like many older U.S. cities, DC has a combined sewer system. During heavy rainfall events the capacity of the combined system can be exceeded, resulting in combined sewage and stormwater discharge into DC’s river.
Phase one of the Clean Rivers Project in the Rock Creek Area of DC, includes implementing green infrastructure techniques such as bio retention (e.g. rain gardens) in curb extensions and planter strips, and permeable pavements on streets and alleys that will can manage the volume associated with 1.2 inches of rain falling on 365 impervious acres of land. Just as underground tunnels are designed to a given holding capacity, the green infrastructure was likewise designed to manage certain volume of rainfall.
The green infrastructure was financed by the first of its kind Environmental Impact Bond (EIB) where both the investors and DC Water, hedge the financial risks and share the benefits. If the green infrastructure performs better than expected at reducing storm water runoff, DC Water will make an outcome-based payment to the investors. If the green infrastructure underperforms at reducing runoff, the investors will make a risk-share payment to DC Water. If performance falls within the expected outcome range then neither party will make a payout.
The results of phase one are presently being monitored and evaluated to understand the green infrastructure efficacy to attenuate the stormwater, although are expected to deliver a range of benefits beyond reducing the occurrence of CSO events. This includes creating local employment opportunities through installation and maintenance, improving the micro-climate and building climate change resilience and reducing crime through greener communities.
This case study offers important insights to other municipalities struggling to manage CSO overflows, and shows how green infrastructure can be implemented, in partnership with other city programs, to achieve win-win measures. In particular, city planners, the water and sewage authority, environmental departments and organizations focused on urban regeneration, climate resilience and mitigation and more broadly environmental causes, can implement green infrastructure to achieve multiple objectives in tandem in a cost-effective way. The innovative financing approach can also be readily replicated in other context.
Agriculture and human civilisation began in the Fertile Crescent that runs from eastern Turkey to Iraq: cattle, sheep and goats were domesticated there; the first figs, almonds, grapes and pulses were planted there; the progenitors of wheat were sown there.
Cities were built, irrigation schemes devised, empires rose and fell. Greece colonised the Mediterranean, Rome later controlled it and set the pattern of law and civic government for the next 2000 years in Northern Europe.
Islamic forces brought a different civilisation to the Balkans, North Africa and almost all of Spain. The grain fields of the Nile Valley underwrote the expansion of the Roman Empire.
“What’s really different about the Mediterranean is the geography. You have a big sea enclosed by continents, which doesn’t really occur anywhere else in the world”
But the pressure of history is likely to be affected by the high pressure of summers to come. In a world of rapid climate change, the already dry and sunny enclosed sea will become sunnier and drier, according to two scientists from the Massachusetts Institute of Technology.
They report in the American Meteorological Society’s Journal of Climate that the winter rains that are normally expected to fill the reservoirs and nourish the rich annual harvest from the orchards, vineyards and wheat fields can be expected to diminish significantly, as atmospheric pressures rise, to reduce rainfall by somewhere between 10% and 60%.
Ordinarily, a warmer world should be a wetter one. More water evaporates, and with each degree-rise in temperature the capacity of the air to hold water vapour increases by 7%, to fall inevitably as rain, somewhere.
But episodes of low pressure associated with rain clouds over the Mediterranean become less likely, according to climate simulations. The topography of the landscape and sea determines the probable pattern of the winds.
High pressure grows
“It just happened that the geography of where the Mediterranean is, and where the mountains are, impacts the pattern of air flow high in the atmosphere in a way that creates a high-pressure area over the Mediterranean,” said Alexandre Tuel, one of the authors.
“What’s really different about the Mediterranean compared to other regions is the geography. Basically, you have a big sea enclosed by continents, which doesn’t really occur anywhere else in the world.”
Another factor is the rate of warming: land warms faster than sea. The North African seaboard and the southern fringe of Europe will become 3 to 4°C hotter over the next hundred years. The sea will warm by only 2°C. The difference between land and sea will become smaller, to add to the pattern of high pressure circulation.
“Basically, the difference between the water and the land becomes smaller with time,” Tuel says.
What is different is that the latest research offers detailed predictions of the nature of change, and identifies the regions likeliest to be worst hit. These include Morocco in north-west Africa, and the eastern Mediterranean of Turkey and the Levant.
“These are areas where we already detect declines in precipitation,” said Elfatih Eltahir, the senior author. “We document from the observed record of precipitation that this eastern part has already experienced a significant decline of precipitation.”
This article was originally posted on the Climate News Network.
A new World Bank study shows that reduced rainfall in developing countries has caused around 9% of cropland expansion and deforestation over the last two decades. The study looked at the land cover and rainfall data from 171 countries over the 23 years from 1992-2015, to see what impact rainfall anomalies (increases or decreases from the average) had on cropland expansion in subsequent years.
It’s well established that periods of drought damage crops and reduce yields for farmers around the world. However, until now little was known about the consequences of such pressures on cropland expansion. The researchers found that in developing counties, cropland expanded for up to five years following a drier-than-normal year. They did not find the same effect for increased rainfall.
The findings demonstrate the close connection between climate adaptation measures and climate change mitigation. The researchers found that regions where water infrastructure, such as irrigation, was present did not show similar cropland expansion. Adaptation measures such as improved farming practices, irrigation infrastructure or drought resistant crops, may therefore reduce the pressure on smallholder farmers to replace forested land with cropland.
These impacts will become more acute in the future as climate change is expected to reduce water availability and increase the frequency and intensity of drought events in many developing countries.