Frontiers of Earth Science

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1:04Katrina was a generational storm and to me a generational storm means that if you are of a certain generation you can name exactly where you were and what you were doing during Katrina.

1:15Roland Pease:The annual global gathering of earth scientists, the AGU fall meeting is not just a chance for them to share their latest discoveries it's also a chance to relearn lessons from past events like the disaster of Hurricane Katrina. That's what I was doing during the day. At night, as Katrina was making its approach, I was reading John McPhee's Control of Nature, a book that was written in, what, 1985, that described exactly what would happen to New Orleans if they got hit by a Category 3. Katrina hit in 2005. My urgent question is the social science question of what does it take for us to take something that we know is going to happen and act on it.

2:03Thanks everybody.

2:05Roland Pease:This was a packed session at last month's AGU meeting, not just because it was the 20th anniversary of the storm, but because the conference was being held in New Orleans, the city on the coast of the Gulf of Mexico that caught the brunt of the hurricane with a loss of 1 ,300 lives and a cost of$125 billion. I'm Ronan Pease, and for this second edition of BBC Discovery from the massive 2025 American Chief of Fiscal Union meeting, I'll be heading back to the beginning of life, to the fate of ice at both poles of our planet and to the end of the Mississippi, well, south of New Orleans. But we're starting with those lessons from Katrina 20 years on.

2:501.5 million people did evacuate. 80 % of the community evacuated. The levees broke and over 245 ,000 homes flooded because the storm overmatched the infrastructure. You can build a 50-foot levee and a 55-foot storm come and you got a disaster. So what happened in Katrina could happen again and it happens all along the Gulf Coast because Mother Nature will break anything built by me.

3:18Roland Pease:That was Lieutenant General Russell Honore, who became a hero for his efforts in the wake of the Katrina disaster. It was a justifiably long debate they held at the meeting on what went wrong in 2005, on how hurricane forecasting has improved, and how disaster planning has changed since. Because, as one of the organisers, New Orleans-based climatologist Jill Terrapanier told me Katrina marked a tipping point in our understanding of the threat from hurricanes. It has a marked almost living memory in every person that is from New Orleans or who has studied hurricanes and that type of tropical system for the last 20 years.

4:02And I think so much of it was, as was mentioned today, quite a surprise in that it was a category three in a place that had habitually experienced this, but not the slip of the levee structure that then led to the massive inundation of the Ninth Ward and the rest of New Orleans.

4:20Roland Pease:What's come across from me is, I guess, maybe three levels of failure. One is the engineering one. There were these protections built around the city that weren't up to the occasion. It feels like the science wasn't there to expect that this was actually going to come. And I'd be interested to have that change. but also there was the social aspect of the response. It was a slow response. Yes. The city was cut off, the communications were down. Just unpick that a bit for me. I think there's a combination of all of the above. The science, while there were individuals that spoke about how coastal New Orleans had a high risk from an event like this as published in the 1980s and even in the early 2000s, right before the event, the science was there but the communication was not.

5:09And so the idea that policy and community structure would change as a response to the science was still highly delayed. And a lot of the advancement is about understanding that the line of communication in all possible directions has to be opened, and that in New Orleans, the response and then the slow recovery afterward was a highlight to how poor the communication was at the time. So the engineering concerns and issues paired with the lack of science communication at the time, add that in with the lack of societal infrastructure changes in response to what we had learned, you have this 20-year generational disaster that manifests itself.

5:51Roland Pease:I mean, one of the things I heard was that they did successfully evacuate 80 % of the city. That leaves 20 % who didn't make it. I have seen in more recent hurricanes, these vast use of people moving out. Has the forecasting and has that social side, that social science side got a lot better that people understand since Katrina how dangerous it can be? Yes, which is a phenomenal advancement from a tragic situation. A great example is Hurricane Laura, which was a couple of years past. In the response, a few days ahead of time, The National Hurricane Center warned that the storm was going to make landfall approximately three to four days ahead of time, which is pretty substantial as far as allowing for approximately two million people to get out of the area.

6:36That communication that occurred as a response to hurricane scientists paired with the actual politician that has to release that evacuation order and then society's response to listen, it worked. And so there are some incredible advancements. You will still see threats. You will still see loss because there will always be failures. I believe that we are unable to anticipate. That's part of what that catastrophe insurance is about. But if we can get to a point where it's less and less every time, then we're doing the right thing.

7:09Roland Pease:Well, I just have one question on that. Have we got a kind of a red queen effect that at the same time as the science is getting better, the engineering can improve the awareness, the risks of more intense storms, the rising sea level making defences harder and so on. Is it sort of a race against? Well, isn't that always? I feel like that's a little bit always the way science and understanding of human progress works. Yes, we see storms getting worse. But yes, the awareness is better and the communication is more advanced. so ideally we at least stay toe-to-toe as close as we can. I think seasons like 2025 lead us to a touch of complacency along the Gulf Coast which is always dangerous to remind ourselves that it isn't every year we see low numbers of storms and that it's a cyclical situation but I think that's a big part of it is trying to know where we are in relation to the changing events and New Orleans is kind of ground zero for all of it actually.

8:06Roland Pease:Hurricane expert Jill Trepanier on the enduring lessons from Katrina 20 years on. New Orleans is vulnerable to storms in part because it sits low on the delta at the end of the Mississippi River, over three and a half thousand kilometres long and draining 32 Midwestern states. The delta has swollen over millennia as the river dumps sediment into the Gulf of Mexico. What I learned only while there is that the river and delta actually extend far beyond the city with a finger-like protrusion into the gulf called the Birdfoot Delta and that that is threatened by human activity and sea level rise. Louisiana State University's Carol Wilson is part of a consortium trying to protect this overlooked extension of the Mississippi.

8:53You've got at least a hundred river miles to go till you even get to the Gulf of Mexico. It takes a while to get out there all the way to the edge. These are places that you could drive. It seems like the end of the world. Like right now, I could probably drive. It'd take an hour and a half. And then you'd have to get on a boat. And then you'd have to be on that boat for another hour. And then you'll be at the Gulf of Mexico.

9:17Roland Pease:And you call it the Birdfoot Delta because... Well, we call it the Birdfoot. And that's really, it's the actual terminus of the Mississippi River. So the very, very end of the line basically. So much of lower Louisiana is what we would consider the Mississippi Delta, but some people only look at the very, very end and that's what's the bird's foot. And we call it that because when it gets down there, it spreads out into these three channels and they literally look like a chicken foot. So it's mostly a river, it's mostly water, but it's got these wet lands and so on in between. It's an amazing landscape.

9:51So when a delta builds, usually this river is carrying with it sediment in there, and those could be different grain sizes. And whenever it first gets to its opening, it'll start dropping the sediment first. And so that has to kind of pile up a bit, but then plants can start building on top of that sediment. And these plants in this area, this is marshes, we're in a temperate zone. If we'd lived closer to the equator, we might have more mangroves here. But right now it's mostly marshes, which are grasses, and those start building on that landscape and they actually help trap the mud too so it's kind of like a feedback mechanism where they're helping build the landscape and build it out horizontally but they also help build out the land vertically because we do have a problem here where like the rest of the world there's sea level rise happening but deltas are very special landscapes where all the sediment has been deposited and there's a lot of load put on the earth so actually the land surface is going down.

10:49Roland Pease:So it's being weighed down at the same time as the sea levels rising. Same time as sea levels rising. So we call that relative sea level rise here. And we have relative sea level rise rates here that can be on the order of, let's see, some places it's almost three centimeters per year. So many places are measuring sea level rise in millimeters per year. We can measure it in centimeters per year. It's huge. And the other thing I gathered was the big difference from let's say 100 or 200 years ago is that the Mississippi River has been dammed so that's reducing the amount of sediment coming down and then the main channel through the middle of this Bird's Foot Delta is being dredged so that ships can get in and out all the time.

11:32Part of our problem has been that we've strangled the river and we don't allow the sediment to go where it needs to go. So I am a proponent of trying to get sediment from the water out past where people are living and back into those marshes and trying to restore what was naturally there, giving them essentially a fighting chance against relative sea level rise.

11:55Roland Pease:The one other threat which I'm sort of aware of is the Gulf is where all the hurricanes are building up. There was Hurricane Katrina 20 years ago. There have been quite a number of others, I think, since here. I mean, And does a delta like this actually make a kind of buffer against some of the storm surge, for example? Absolutely. That's probably one of the most important things that we try to teach our students in classrooms and the public is that wetlands are natural speed bumps, if you will, for storm surge. They absolutely do slow down the wave energy and they can diminish a storm surge wave.

12:28So think of it like with a mile of wetland, it might diminish your storm surge by one foot or so. So that could be significant if you've got several miles of wetland between your community and the Gulf and you have a storm coming. And if those wetlands start deteriorating, that kind of protection starts to diminish. And then you have to rely more on human structures to protect you.

12:51Roland Pease:But nature does it better. Nature will always do things better. It's an unfortunate thing. And I think it's something that we should realize also. So it's definitely cheaper to help maintain a landscape that is already there than it is to have to rebuild it once it's been lost. Carol Wilson looking for ways for humanity and nature to coexist. The reminder, this is Discovery from the BBC, reporting from the mega American Geophysical Union meeting just held in New Orleans. This is summer at its peak. Whole Foods Market Summer Fruit Fest is your invitation to eat the season. Fresh, organic, and bursting with flavor.

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14:24Roland Pease:Much of what we understand of global climate change is based on comparisons with past climates as revealed by air bubbles trapped in ancient polar ice. The best known of these comes from the three kilometre deep Antarctic ice sheet extending back 800 ,000 years, covering several glacial warm cycles of climate. The trouble's been that the weight of three kilometres of ice melts anything deeper, which is what's limited how far back these cores can go. But a project called Coldex has been looking for rafts of more ancient ice that somehow escaped that melting fate, claiming last October to have recovered six million year old ice.

15:09Roland Pease:There, Ed Brooke came to AGU to share the excitement.

15:15So this is a piece of Antarctic ice. And this is ice that formed when snow fell on the Antarctic ice sheet about 50 ,000 years ago. I can see the bubbles in it. And those bubbles formed when the snow fell and then compacted by the weight of the overlying snow and trapped the ancient air. So it's not like bubbles in your soft drink.

15:36Roland Pease:Those are little time capsules of ancient air. I mean, it's pretty magical to think that this ice cube has been sitting around long before we had farms. This is back in the last ice age. And this is not the oldest ice. We are working on ice that's millions of years old. But we can't bring that along for show and tell. Where's this actually come from? Just give me a sense of the location. Yeah, you know, getting this ice cube here to the United States is an involved process. We're out in the wilderness in Antarctica in deep field camps with ice coring drills, which are these big mechanical devices that drill cylinders of ice into the ice sheet.

16:18And we pull those up every day. We might get 20 meters or so. Then we drill again and again and again. So we do have to pay a lot of attention to get it home. We fly it to McMurdo Station. We put it in freezer containers. It goes on a ship. It comes back to the U.S., monitoring the temperature all the way along. And then we have a very large facility in Denver where we store these ice cores. And we have ice cores from the 1960s that we still use. So it's really an archive for science for a long time. You keep on going back, though, to get more. We keep on going back to get more because the scientific problems change.

16:54And our particular work right now is trying to find places where the ice is way, way older than we've ever found before so we can explore the Earth history going back in time.

17:05Roland Pease:But the bit that I still don't understand, and that's why I was interested about where it is that you've actually got this from. As I recall, the way it's worked so far is with the ice cores they have, they drill down through the ice, through the ice, through the ice, until they hit bedrock, and that's the oldest stuff, and that's 800 ,000 years old. So have you got ice that's way older than 800 ,000 years? The ice we're working on, the really old ice, comes from a special place where the ice that is flowing from the interior, because the ice from the interior is always flowing out towards the edge, has gotten trapped in the mountain ranges along the edge of the Antarctic ice sheet.

17:41And there are special places where ice has stagnated and just kind of got stuck there. So the searching was a little bit of needle in a haystack for a while. And we found places where the ice was old, and we've been sort of leapfrogging around trying to find even older regions in the same general location. And right now, right as we speak, we have a team drilling two more ice cores at Ellen Hills with some new tools to get even deeper and more high-quality cores.

18:12Roland Pease:So this is really going to go places? Yeah, we think so. We have a lot of new results coming out soon. And, you know, our aspirational goal now is 10 million years. We'll see how far we get. That would be long before humans started to evolve and when CO2 levels will likely last as high as they are today. Keep an eye out for Ed Brooks Coldex data. Towards the other pole, Greenland is home to the planet's other great ice sheet, rapidly melting because of global warming. If it goes completely, which would take thousands of years, it would reveal landscapes that last saw sunlight two or more million years ago.

18:51Roland Pease:But thanks to some fancy maths presented at AGU by Alison Chartrand of the University of Maryland, we can imagine the hidden mountains and valleys from the shadow of an impression that they leave on the ice sheet surface high above. Her motivation? First of all, just knowing how thick the ice is is really important. And if we don't know what the landscape looks like beneath the ice, we're limited in our ability to measure the ice thickness and thus the ice mass and thus in the future how much might go into the ocean and cause sea level rise. But we're also interested in it because we can look back into the past and figure out how the ice sheet might have formed, where it might have incepted, where we might be able to find really old ice for ice cores so that we can get more climatic clues about the past.

19:38Roland Pease:So if you've got a really deep bit, that's likely to have older ice, you mean? Yeah, exactly. So there are a lot of reasons to be interested in the subglacial landscape. What caught my attention was that you said there are vast networks of valleys under the ice. What do you think they look like, as it were? Give me a sense of that. So, for example, in the alpine regions in Greenland, especially in eastern Greenland and southern Greenland, we have a lot of really steep alpine topography that's really well preserved. And we think that that's because the ice has been there for so long and it's always been really cold there.

20:11And so there's not a lot of water that's flowing under the ice to change the shape of the valleys. The glaciers aren't moving very fast there. And so there's not a lot of erosion there.

20:20Roland Pease:I mean, when you start talking about alpine, I mean, should I think of these valleys as if they were, you know, these steep Vs with rocks over? Oh, yeah, like scale. Yeah, they're like hundreds of meters tall in some cases, like in those steep alpine spots. And how are you seeing through the ice? Because presumably these are, in a lot of places, buried under hundreds if not thousands of metres of ice. Yes, exactly. So we can see through the ice using radar, but what I did was use some really complicated equations called bed-to-surface transfer that relates the bed topography to the surface topography and the surface elevation.

20:57Roland Pease:What you mean, so even though there's all that ice, somehow the ripples on the surface reflect the rocks underneath. Yes, exactly. It's pretty crazy, and it's because of the way ice moves. It's semi-viscous. It's sort of slightly sliding. Yeah, it's kind of like a waffle iron. So if you're pouring batter into a waffle iron, you can kind of see where the divots are in the waffle iron and that it's the same sort of principle with the ice sheet. There's a lot of math, I suspect, going from the ice surface. But I love that. There's sort of the shadow almost of the valleys underneath. Yeah, exactly.

21:31Roland Pease:Reflected in the surface. Yeah, because we have these great math equations, we can understand what the big valleys look like underneath. If I had some kind of magic machine which could just lift this ice in one place, I mean, is there a particular region that you'd just sort of love to go and look at in detail? Sure. I mean, the whole thing. I have been really fascinated by the Jakobshaven drainage catchment, which is the fastest moving glacier in Greenland. And that's where we see in the new map a lot of really interconnected valleys, a lot of extended valleys from the valleys that we could detect before.