Microbiomes control blood pressure, and the cost of water
This month, evidence that the microbiome is controlling blood pressure - so will we treat hypertension with probiotics in future? Also, plastic is everywhere and an urgent environmental threat, but is the public aware, or do they care? We also consider the economics of animal extinction and species conservation, the price we pay for water, and the role of the "blue carbon" in keeping CO2 in check...
In this episode
00:52 - How the microbiome affects blood pressure
How the microbiome affects blood pressure
Bina Joe, University of Toledo
Inside each of us is a thriving family of microbes that outnumber our own 37 trillion human cells at least twofold. Together they weigh in at over a kilo, and some scientists now regard this microbiome, as it’s known, as an organ in its own right, and also one of our greatest medical oversights, dismissed for decades as mere colonising microbes. But in recent years we’ve begun to realise that the suite of thousands of biochemicals released by these bacteria and fungi, and the metabolic knives and forks they bring to our digestive systems, are crucial to health and disease, determining even our blood pressure, as the University of Toledo’s Bina Joe explains to Chris Smith…
Bina - We are working on the microbiome and we are looking at how this microbiome influences blood pressure hypertension, which is the number one risk factor for cardiovascular diseases. And our lab was the first to discover that the tiny bugs that live in our guts actually tweak our blood pressure.
Chris - What's the evidence for that association before we think about how they might be doing that, what's the pure evidence that they are even doing that?
Bina - I will go back to my first publication where we did this experiment. We took a rat with normal blood pressure and asked, if its microbiome is perfect, then can we then take its slurry of bugs in its gut and add it to animals that have high blood pressure. But to our astonishment, what happened was it did not lower blood pressure, but it further increased its hypertension, which was the first piece of evidence that these bugs are doing something to the blood pressure of these animals.
Chris - Is there wider evidence that this is not just a laboratory phenomenon though If we look in humans, can we see signs that what lives in us may be influencing our blood pressure?
Bina - Absolutely. So following our animal experiments, human geneticists started exploring this idea and find associations of gut microbiota, which is the bugs in our bodies with people's blood pressures. So there are considerable studies now showing this as conclusive association in humans. The point association is it's difficult to prove causation, and therefore we go back to the animals and then show that when there are animals which don't have any bugs in them and then you introduce germs into them, blood pressure increased. So that was the causative evidence that we went after for what is the next mechanisms question, right?
Chris - Indeed. So if something causes something to happen, there must be a plausible biochemical mechanisms. So what do you think they might be doing that would manipulate the blood pressure in a host animal?
Bina - That's the million dollar question. I wish I could answer that. These microbes generate thousands of biochemicals and they secrete them into our bodies. So we are looking into which one of these chemicals that they make affect our blood pressure. We don't have answers yet. We have a few indications of some metabolites, but not all of them. And that's where the research space is currently.
Chris - Over the years when we've learned then that diet has a really important role to play in cardiovascular disease. Mm-Hmm. <Affirmative>, do you think a contribution of our diet is that the microbes digest our dinner and they make biomolecules, which then in turn affect our disease risk?
Bina - Absolutely. That was how we started this research. Think of salt, it's the number one dietary factor that increases blood pressure and salt is used for ages to make pickles. So salt kills bacteria. Think of consuming salt and that rearranging your, the population of the bugs in your body. That's exactly what it does and that's where it got fascinating for beyond diet. What else are we eating to kill bacteria? Classic example, antibiotics. Are we consuming antibiotics and changing our physiology? Yes we do. In our animal models three different antibiotics that we tried actually raised blood pressure in our animals and that's alarming before they went and asked, is it all the antibiotics or only some we tried amoxicillin because it's used in children so often and at least in our animal model, amoxicillin was the only one that did not increase blood pressure. So we are saying that might be the safe one, but other antibiotics did raise blood pressure. Then you can expand it to what are the environmental agents? There are so many herbicides we decides that we use, they are to kill plants, but they also kill microbes. So are we exposed to agents that destroy our microbiome? The answer is yes.
Chris - And to what extent might these effects be permanent? Because we use a lot of antibiotics and we almost certainly are demolishing people's microbiomes for a while when we do that. Does that leave holes in the microbiome when it comes back, which are going to set people up to develop some of these conditions, or do they fill in those holes and reacquire the missing microbes again, so antibiotics are a short term curse, but it's only a major problem if you're on them for a long time?
Bina - I referred you to a paper that came out in Nature a few years back where they compared paleo faeces, which is 7,000 year old poop samples and compared the microbiome in that sample to modern day industrialised world with some European countries represented and with underdeveloped nations and developing nations microbiomes of humans. And they found that the ancient microbiome aligned with the underdeveloped and developing nations develop microbiomes better. Which means clearly that the industrialised nation, which there is maximum exposure to all the environmental agents that I was talking about, including antibiotics usage, we have probably changed our microbiome drastically...
Chris - Do you foresee then a time coming where when we assess a patient rather than just give them another anti-hypertensive to try, we will be looking at their microbiome and asking what can I add or what can I subtract microbe-wise - through probably giving different food stuffs to manipulate the microbiome - and that will have as much efficacy as some of the pills we give people?
Bina - Absolutely. Chris, I'm a believer in this for hypertension, we have been focused on genetics for too long to look at genes in our bodies that are different variations of which are associated with human hypertensives. Right? But that's only 30% that can explain the incidence of hypertension. So what is this other 70%? We have been looking at the environment and we bring in microbiome as a new less appreciated in the past discovery piece for, to look at or what I'm trying to say is it's not just treatment with pills. Another thing we have done is we have inserted an antihypertensive gene called ACE II - angiotensin converting enzyme II - to bacteria lactobacilli and gave it as a probiotic to our animals and it's able to lower blood pressure. So there are opportunities for manipulating microbiota and using them as pills if you may want to before you develop hypertension.
08:49 - Public perceptions of plastic pollution
Public perceptions of plastic pollution
Tony Walker, Dalhousie University
Each year the world produces about 350 million tonnes of plastic. In total we’ve made about 8.3 billion tonnes: one tonne for every person alive today. Although some is recycled, there are limits, and most of it ends up in landfill, the wider environment, and the oceans, where the health impacts are only just beginning to become apparent. But what do members of the public think about plastic pollution, and does public sentiment have any leverage to address the problem. Inspired by a recent session he chaired at a conference on this topic, these are some of the issues that Tony Walker, who is at Dalhousie University in Canada, has been exploring, as he explains to Chris Smith…
Tony - In terms of you know, the, the public's ability to do anything about it many members and, and, and results really from this study, it, you know, a lot of people feel powerless because its corporations and governments and, and you know, consumerism: we're part of the problem, we like convenience. Producers are producing this stuff. We don't really have the decision-making powers in order to curb that. Governments do. Next week, coincidentally, the fourth intergovernmental panel negotiating committee meets in Ottawa to come together to develop a legally binding plastics treaty. So governments are aware of this now, but it seems public opinion and public perception has, has been on the increase since around 2015.
Chris - What has driven the massive explosion in all of this consumption though, because I just looked at my shopping that I did last week, and to be perfectly frank, after I'd cooked an evening meal, the bin was overflowing. And I don't eat loads of ready meals and that kind of thing. I was cooking reasonable food, but it's all coming almost obligatorily in huge amounts of plastic, and you end up throwing equivalent volume to what you bought in the bin.
Tony - That's absolutely right. And even with your best efforts, it's really hard to avoid plastic and plastic packaging. And the material you are talking about is exactly the kind of things we were asking our general public across these different countries. And it relates to single use plastic packaging, essentially the stuff that we can find alternatives for. And, and in many cases, things we can do without and avoid, but in fact, we can't avoid them because manufacturers, grocers, retailers, they stock their products in these items on the shelf, and it's really difficult to avoid. Even with the best intentions, like you mentioned.
Chris - What's the way to predate this then?
Tony - So we have seen a change in marketing and production, especially a 20-fold increase in plastic production since around the 1950s. And much of that has been driven by convenience and plastic packaging, the sort of, you know, food packaging we're talking about. That's grown and, and we've become to rely on it as convenience. But where we can change is introducing sustainable alternatives. And I would add a word of caution there, because there's no need to switch from one single use item to another single use item because everything really has an, an environmental footprint. But to move towards reuse systems - so reusable bags and reusable packaging - or even dispense with packaging altogether, instead of, for example, bananas wrapped in plastic bags. Why not just have the bananas in bunches and just weigh them they're perfectly packaged in their own their own skins!
Chris - I was gonna make that point, which is not about the bananas, but about bags, because about 20 years ago, supermarket shopping bags, plastic bags that were just given out with abandon whenever you did your shopping. This became a focal point of public disquiet, and a strong campaign was mounted, wasn't it? And we saw supermarkets introduce pricing and charging for those things. There was a shift towards using bags for life, let's say. It seems though that we've, we've been very virtuous on that front, but then supermarkets have instead insisted on force feeding us all our shopping now wrapped up in the plastic. So even though the bags aren't being sold or given away at the checkout, everything else is still plastic wrapped. It's almost like we've robbed Peter to pay Paul!
Tony - Yeah. And again, that's a great marketing ploy behind the scenes with the, the kind of oil and gas companies, the petroleum companies, because 99% of all plastics, consumer plastics, are derived from fossil fuel feedstocks. And of course, with countries and consumers switching to fuel efficient cars and, and fuel efficient homes there is you know, a shift now and a push to market petroleum products in the form of single use plastics. And so here we are, everything is, is wrapped in, in some form of plastic. And what makes it incredibly difficult to recycle at the end of life. You know, you mentioned your bin overflowing, most of that is landfill, and very little of it is recycled because it's complex it, it contains different colored plastics, different chemicals, and indeed, in many cases different types of plastic. So they can't be recycled because they're already mixed. So it is is a very complex issue and it's, it's something which has been forced upon consumers really by by producers and retailers.
Chris - We've talked on this programme before about the health impacts of some forms of plastic. People are very worried about their health, more so than the health of the planet even. So do you think that might be one way to get at this, to say to people, look, this isn't great for the health of the planet, but it it may also have consequences for human health in certain circumstances. Let's try and avoid it. Let's motivate retailers not to do this?
Tony - Exactly. And in fact, that's, that's something that 8 billion people have now recognised, and they've had their own eureka moment, if you will. Because they're recognising it's not just impacting fish and, you know, wildlife that they've seen entangled or ingesting plastic. I mean, that's bad enough. And that raises public awareness in and of itself. But when it really affects people and affects your families, then of course the penny drops. And, in fact, your listeners may or may not be aware, but there was a report released in March and it documented at least 16,000 chemicals, different chemicals, that are used in plastic manufacturer across the entire, you know, various plastics, of which 25% of those are known to be toxic and harmful. And so none of this information is really disclosed by producers, and many manufacturers of food products wouldn't know what the packaging's made of, but the plastic producers do, but it's not released to the general public. And so I think it's important to recognise that whilst we don't know the name of every single unpronounceable chemical compound in those plastics, 25% of them are known to be harmful. And I think we really do need to do something about that.
16:23 - Economics of extinction and species conservation
Economics of extinction and species conservation
Iain Fraser, University of Kent
When we think about a species going extinct, invariably our minds jump to over-exploitation, or poaching, environmental destruction and habitat loss, and climate change. Only rarely do we tend to think about the economics of species loss, which is what Iain Fraser, at the University of Kent, has been urging us to do. As he explains to Chris Smith, translating the mechanisms of extinction, conservation and species preservation into economic terms can, he thinks, helps researchers and policymakers to understand why species disappear, and what needs to be done to reverse the losses that we are currently experiencing. “Correctly valuing species within the wider economy,” he says, “is key to reversing many of the pressures that cause their decline”...
Iain - Fundamentally the biggest problem we face as a society is we've got many competing wants and we've got limited resources. And so if we've got to make some hard choices about what we want to spend gas resources on, so every pound we spend on say schools or universities or hospitals, that's a pound we can't spend on something else. And so when it comes to species conservation and basically thinking about species extinction, we have got a limited budget. So we do have to think very carefully about how we allocate the scarce resource in such a way that we try to make the most of what we currently have. Some of the basic economics of species extinction tells you that if we don't set up our institutions and our, if you like, the context in which economic activity is undertaken in, we can very quickly, you know, give individuals, producers an incentive to overharvest. And by overharvesting, say like fish, we can effectively drive a particular species to extinction. So even if we can understand that they're valuable and we would like to keep them, we sometimes just get it very, very wrong.
Chris - It's also not quite straightforward in the sense that you gave an example if a fish is something we want and we take too much of it, we can drive it to extinction. On the other hand, if there's an environment that the fish lives in and we want something from that environment that the fish also wants and we take the thing away from the fish, the fish will also go extinct but not 'cause we want it. So it's more complicated than just supply and demand?
Iain - Yeah, absolutely. So driving something to extinction, you know, is quite difficult. So, you know, there are examples of introduced species. For example, in New Zealand they have lots of possums, which they don't want because they have a detrimental effect on that particular environment. Actually harvesting something to extinction is actually quite a difficult thing to do. So it does tend to be if we however then make a mess of the environment or we reduce the environment that can support these species, that's probably along with our inappropriate management in terms of harvesting that's going to do it. So yeah, the, the things do happen in tandem and very often it's, you know, it is often the loss of, if you like, the appropriate sort of supporting environment that really will be the deep down core reason why we see extinction as opposed to, you know, us really trying to drive something to extinction by inappropriate harvesting.
Chris - And is the the purpose of your argument that if you can arm people who are like policymakers or lobbyists trying to influence policy makers with some tools that will enable them to translate the message, the environmental message, into a financial slash economical message, which is often something that policy makers are going to understand and engage with better?
Iain - To a certain extent, yes. We can try to, if you like place value, I think this is what you are really getting at here on the particular species. The species themselves may have value as we would see it as economists in and of themselves, but also they would have value to us. If we can demonstrate value in the myriad of ways in which we can think about value. 'cause It's, there are, there is values as we see as economists, but there are other groups, other researchers, other academics will view view value in other ways. But if we can demonstrate value and we can make people sort of conscious of that in their decision making, the hope is they make better decisions. It's when typically we really undervalue something or the value of something is not fully appreciated, that we tend to make these, if you like these mistakes in terms of the way you manage species.
Chris - And what about when we go too far? We come to the party too late in our realisation, oh dear, we have gone too far now we're going to try and "de-extinctify" - I don't know if I made a neologism there, but you understand what I'm getting at! We try to reverse what's occurring. Is that something that could be factored in as well? There must be an economic aspect to that?
Iain - Yeah, there is. We do have, you can think about that in terms of, so within the sort of that, the way of thinking about trying to recreate a population or trying to, if you like, sort of widen the gene pool of an existing population of a very small number of particular say animals within a particular species type. They, we will find examples of what you might call translocation. So I've done bits of work with people at the university where we were looking at translocating a bird species onto a second island in the Seychelles because the particular bird species in question was only on one island. And so in an attempt to increase the population to give it more if you like, sort of hopefully more resilience going forward by creating a second population and increasing the numbers, we will hopefully then be able to, if you like, reverse the possibility of extinction occurring. And you can put economics into the analysis of that. You can think about the, the cost of creating the environment. You can think about the cost of actually moving species. You can also think about the risks involved in trying to move species that, you know, you can't just simply pick something up and move it somewhere else and expect it to, you know, necessarily be able to survive.
Chris - And so what's the take home message off the back of having assembled this? What's the message that I should walk away with?
Iain - I think in terms of when we are now thinking about the general interaction economy and environment, we used to very much think that economics viewed the environment as something to be consumed. Whereas clearly really the way we should see it is the economy sits within the broader environment and they are clearly interlinked. And in many ways our sort of inappropriate or misuse of resources and species in general and the reasons why we see things being pushed to extinction is because we've had that almost sort of that consumption perspective on these things that we can just keep taking as if they're manner from heaven. But clearly we have to realise they're interlinked. And I think that's probably the big take home message here, which is, you know, we have to realise that the economy will benefit or we will benefit from having the species and having more species. And at the same time, we as consumers will also benefit from having that sort of underlying biological resilience as well, which is, you know, imperative and important for maintaining the sort of the world of society we want to live in.
23:29 - The economics of water supply
The economics of water supply
Quentin Grafton, Australian National University (ANU)
Let’s now look at the most abundant chemical on the planet: water, and its inequity. Compared with someone in certain Third World countries, where every drop counts, if you live in a developed nation like the UK, you probably don’t even give it a moment’s thought when you turn the shower on, fill the bath or wash the car. As the world population rises further though, and climate change limits where we can live and how much water is available, the price and value of water will matter increasingly to all of us, regardless of where we live. And that means that we need to think about the economics of what will become a supply-limited resource. Which is what Quentin Grafton, speaking with Chris Smith, has been considering, by asking 5 key questions: why water is, or is not, priced and valued; what are the key economic concepts behind pricing water; how are water supply assets valued for full cost recovery, who bears these costs versus who enjoys the benefits, and when will the price of water change…
Quentin - We need to price water, because if it's not priced, there's the tendency to not conserve it, not look after it, use too much. And that's true, whether it's you're a farmer, whether you're a household or an individual. The value is really around the different uses of water. Whether it's, you know, for drinking - very high value - or whether it's for the garden which is less highly valued. So that we know if we have to prioritise water across different alternative and competing uses, we want to make sure it goes to the highest value possible. In places that don't have much water, which is good part of Australia, the priority always goes to drinking water. And then you set up all your planning, all your water infrastructure to make sure that's where it goes.
Chris - So what are the key concepts that economists should use then when trying to come up with a pricing strategy for water?
Quentin - The issue is really around marginal cost and marginal benefit. Marginal just means some incremental amount of water that's delivered to me as a farmer, to a household. And the cost is, well, how much did we spend and expend to actually get that delivery? So that's marginal cost. And the other concept is this idea of marginal benefit, which is really about what extra we get from consuming water - marginal benefit and marginal cost - whilst making sure that the essential uses for water are available to everybody.
Chris - So how should it be priced then? Because also it's going to really vary according to where you live on earth. Whether you have a too much water problem or a too little water problem, or no money in your, in your pocket, some money in your pocket.
Quentin - I have lived in a number of cities around the world. So one is Wellington New Zealand. Now there in those in the city of Wellington, you don't pay a volumetric price for water. So what that means is that a lot of people will waste water and also the suppliers of water in Wellington don't have the incentive to deal with water that gets lost in the pipes, that doesn't actually get to the households. Compared to where I live in can Australia, we pay very high volumetric prices in Canberra and that ensures that we have the right signals to look after the water in the sense that we are not going to waste the water.
Chris - How does that though incentivise the people who are delivering you the water to make sure their pipes aren't leaky? Because I saw a staggering statistic for UK water supplies recently, which suggested that the amount that actually comes out of a tap somewhere is only a fraction of the amount that went in. It's not like losses are a little bit on top. It's like there are losses with a little bit of delivery on top.
Quentin - A part of the problem is if you're not being paid as the supplier per amount of water of litre that you're selling, so to speak, the incentive to do something about, it's just not there. Compare that to Canberra. If you are getting paid per litre, the water supplier in that context has every incentive to deal with those leaks and leaky pipes because they're gonna get much higher revenue if they actually deal with 'em.
Chris - Ultimately, it comes down to the who though, doesn't it? Which is one of your other questions. Who is, is benefiting or, or needing the water? And there's the staggering statistic in your review that half the world population are in water crisis at least once a year for a month or so. So how do we sort this one out given where people are, the massive scale we're dealing with and the unpredictability with climate change and other things in the source of geographies that we're gonna have to consider?
Quentin - Well, it's a water supply issue in some sense. The water is, needs to be accessible and an affordable price, and that's an infrastructure story. But that story is also not just about pipes, it's also about protecting wetlands. It's about protecting upper catchments, you know, with forest. So you actually maintain quality water in terms of not having sediment in it, for example. And then you also have this whole issue around making sure that yes water's affordable, yes, that it's safe, but also, that the costs are covered. So we need to deal with that. And that is around pricing, but it's also around water values as well, key values. And the highest value is really drinking water and not just for people living in, in big cities, but also people on the fringes of the urban areas and also people in rural areas. That's the missing dimension to it.
Chris - So is your approach here that when a country is looking to try to improve its water situation, they should be thinking about these economic principles and then there's a sort of a framework for them to follow, which hitherto has been very ad hoc geographically.
Quentin - Exactly right. So I mean, if I were to say there, you know, the four pillars really in terms of how we should respond to the water prices in the context of water pricing and values, you know, we need, we need to get cost recovery because the person supply need to get their cost covered, otherwise they're not gonna supply. So that the price that people are paying, it's transparent and it also covers that, that extra cost to bring it into your household or to your farm. Basic water needs need to be met. And then the last but not least is consumers need to be incentivised and that's where water prices come in. So they incentivise to conserve water, not to waste water, not to over-extract water. Those are the things that pricing can do that can be done and has been done in both rich and poor countries. So we can do this. It's something that we can fix certainly with an urban context and anywhere in the world it becomes more challenging in rural areas 'cause it's much, much more difficult to just supply accessible safe water in the whole parts of the world. In remote communities, for example.
30:26 - Blue carbon and climate change
Blue carbon and climate change
Kerrylee Rogers, University of Wollongong
Of the billions of tonnes of carbon that we emit annually, a significant proportion ends up, ultimately, in the sea where it contributes to so called “blue carbon”. This is carbon locked away in marine and coastal ecosystems. By soaking up carbon, they help to mitigate against climate change. But they may themselves fall victim to climate change and one of the other consequences of global warming: sea level rise. Speaking with Chris Smith, the University of Wollongong’s Kerrylee Rogers has been looking at the present, past and future of blue carbon…
Kerrylee - Blue carbon is the carbon that's sequestered by marine ecosystems. When we use the term sequestered, we are really talking about carbon being trapped for long periods of time. When we're talking about marine ecosystems, we're really talking about mangrove forest and salt marshes and seagrass meadows. They're the biggest blue carbon stores that we have, and actually, mangrove forests are amongst the most efficient ecosystems at sequestering carbon from the atmosphere.
Chris - When we're talking about things like mangroves, how long can they lock away carbon for? Is it long, long, long times like oil and coal or is it just a temporary holding measure for carbon?
Kerrylee - Probably a bit of all of those things actually. So there is some carbon that gets pulled into the mangrove woody material, and, if a forest drops some leaf litter, that organic material might break down relatively quickly and returned back to the atmosphere. Then you've got carbon that is pulled into the root zone. So this is the plants as they photosynthesise, they grab the carbon and they're adding organic mass to the structure of the tree, and some of that is below ground in the roots, and that material can stay for a lot longer because it's below the ground surface. So it doesn't sort of get distributed away on tides like leaf litter might. And it's locked away from exposure to the atmosphere to some degree. And this exposure is partly because those roots are covered up with sediments, but also because tides come in and out relatively regularly, as those tides come in, they actually make the substrates really waterlogged. And for decomposition to occur aerobically, you need air in the substrate. With tides coming in all the time, it stops the availability or limits the amount of air that's available within substrates, and that then slows down the rate of decomposition of that organic material or that root material that's down below the, the substrate surface.
Chris - So it is a legitimate way of locking up carbon for a reasonable length of time?
Kerrylee - Yes, in the right circumstances, and the right circumstances don't occur everywhere. What it really requires is that carbon getting locked away for a really long period of time. So it means they can't, the sediments can't be eroded. It also means that they need to remain relatively unexposed to the atmosphere and to oxygenation. And that only occurs under sort of special circumstances. So it's where tides are coming in and out all the time, and where that rate of inundation actually limits the exposure to oxygen and also slows down another mechanism of decomposition. So when we have tides coming in, they're often salty water and that salty water slows down another process of decomposition called methanogenesis. This is a process that creates another greenhouse gas, not carbon dioxide, but it creates methane gas. And so that inundation with salty water actually means that those methanogenic processes, those processes that create methane, are also slowed down. So we've got a number of mechanisms that create conditions for decomposition of the organic material from mangroves and salt marshes to be relatively slow.
Chris - On the one hand, then this is a good thing because as we release more man-made carbon dioxide and greenhouse gases into the atmosphere, we've got somewhere for it to go. On the other hand, presumably the changes which are happening to temperatures, to sea levels and so on could be jeopardising this very thing, which is there acting as a sponge to mitigate that?
Kerrylee - Yes. So I guess blue carbon is, is not a silver bullet. It's not the solution to climate change. And it's not the overwhelming solution for multiple reasons. One of them being firstly that the capacity of blue carbon ecosystems to sequester carbon or bring more carbon from the atmosphere is actually limited because of the extent of these systems. We've been cutting down mangrove forests, and urban expansion has occurred across salt marsh flats. And that's slowing down our capacity or limiting the capacity of these ecosystems to pull carbon from the atmosphere. The other issue, as you already touched on, is that these ecosystems are actually at risk from climate change themselves. They occur right near the sea. They're roughly at near mean sea level. And if mean sea level is rising, these ecosystems also have to adapt to that change in mean sea level to survive. We've done some modeling work that actually shows that the capacity of these ecosystems to adjust to sea level rise appears to have an upper threshold limit, and we potentially could be hitting those upper threshold limits before the end of this century.
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