This might be because:
Yes, absolutely, although it depends. So I think with the dinosaurs, [the asteroid theory] is quite widely accepted at this point. There was a big paper in Science on this subject last year, although there are still a couple of holdouts. The worst mass extinction of all time came about million years ago [the Permian-Triassic extinction event ].
There's a pretty good consensus there that this was caused by a huge volcanic event that went on for a long time and released a lot of carbon-dioxide into the atmosphere.
That is pretty ominous considering that we are releasing a lot of CO2 into the atmosphere and people increasingly are drawing parallels between the two events. The very first extinction event [the end-Ordovician ], seems to have been caused by some kind of sudden cold snap, but no one's exactly sure how that happened. But then, with the other two, the causes of those are pretty murky and people have tried to come up with a unified theory for these extinctions, but that hasn't worked at all. The causes seem to be pretty disparate.
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Though precise estimates are tricky because measuring that background rate turns out to be very difficult. How did they realize this? I think a point that's important to make is that, normally, you shouldn't be able to see anything go extinct in the course of a human lifetime. The normal background rate of extinction is very slow, and speciation and extinction should more or less equal out. But that's clearly not what is happening right now. Any naturalist out in the field has watched something go extinct or come perilously close.
Even children can name things that have gone extinct. So as soon as this concept of background vs. Now, whether you make the jump to say that a major mass extinction is going on or just an elevated extinction rate, that's up for debate.
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But if you are looking at this in a rigorous way, you can see that something unusual is going on. One thing your book explores is that no single factor will drive current and future extinctions. There's hunting and poaching. There are invasive species. There's climate change and the acidification of the oceans.
A sixth mass extinction is underway - and it's our fault
Which of these stands out as most significant? To me, what really stood out And I always say, look, I'm not a scientist, I'm relying on what scientists tell me. And I think many scientists would say that what we're doing to the chemistry of the oceans could end up being the most significant. One-third of the carbon-dioxide that we pump into the air ends up in the oceans almost right away, and when CO2 dissolves in water, it forms an acid, that's just an unfortunate fact.
The chemistry of the oceans tends to be very stable, and to overwhelm those forces is really hard. But we are managing to do it. When people try to reconstruct the history of the ocean, the best estimate is that what we're doing to the oceans or have the potential to do is a magnitude of change that hasn't been seen in million years. And changes of ocean chemistry are associated with some of the worst extinction crises in history. Are there lessons we can learn from past extinctions that provide clues for what the current changes hold?
A lot of people are trying to tease out what survived previous extinctions and ask what are the characteristics of those that survived. It's called the selectivity of extinction events. Why did some groups survive and others didn't? It turns out to be, 65 million years after the fact, very, very difficult. But speaking very broadly, the species that tend to survive mass extinction events often tend to be very widely distributed, or groups that have a lot of species.
I'm not sure whom that's going to help today, but that seems to be the pattern. In your book you talk about this quasi-experiment in Brazil dating back to the s, where ranchers had down swaths of rain forest at random and scientists could study the effects on species. What did we learn about deforestation and extinction from that? It's in the Amazon rain forest north of the city of Manaus. What happened there was that this area was already being converted into ranches, so in collaboration with some American scientists, they deforested it in an interesting way. They left these square patches surrounded by ranch.
You can see it from the air, it's quite striking. And what you find are variations on this theme of loss. First most of the primate species don't survive in these smaller patches or even in the bigger patches of forest. Then you lose a lot of your bird species. In some cases species leave, and in some cases, when you maroon them in small patches of habitat, their populations shrink, and very small populations are just more vulnerable to chance.
- 1. The Late Ordovician.
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- A sixth mass extinction is underway - and it's our fault | World Economic Forum;
So when people talk about the dangers of habitat fragmentation, on the one hand, a big animal that needs a large range can't survive in a small patch. But it's also smaller animals that don't need that much space become vulnerable to the dynamics of small populations. Did that Brazil project yield any lessons for protecting rain forest habitats?
But also in the s there was this battle about protecting forests, and whether it was better to do it in lots of little patches or in one big patch. And this project has resolved that. The End Cretaceous was associated with Deccan Traps volcanism in India not long after it separated from Africa and bolide impact. This is the only certain mass extinction event associated with bolide impact, but volcanism played a major part as well a one two punch. They were not periods of 'quickly changing atmospheric c02'.
They were periods of slow increases in volcanism. Veron is not a volcanologist. Time proved the volcanologists right, and as usual, the physicists who like to dabble in earth history got it wrong eg: The reefs went extinct, like most other things, because of slow sea level changes there is good correlation betwen sea level changes and marine extinctions , changes in volcanism producing a variety of slow effects-again a very good correlation, but importantly-generally not with C02 changes , bolide impacts really the only one that is 'rapid' , continental break ups eg Triassic , continental joinings well known to reduce biodiversity as previously separate and endemic species compete with and then extinguish each other , and many other factors.
You're selective references to the vast peer reviewed literature on mass extinctions does not give readers the full picture of the state of understanding and history of debate in this field. You present a very speculative study as far more definitive than it really is. Vernon may be right about ocean acidification being the coral killer, but the case is certainly far from proven, and may never be. I think your claim that dramatic climate change always produces mass extinctions needs major qualifications added too. The PETM was a pretty dramatic temperature increase, for instance, but it led only to a very minor marine extinction extinct.
More recently, there have been some dramatic climate changes with no evidence of associated extinctions - the so-called Quaternary conundrum.
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Other experts I've spoken to I've been writing a related article say this could just because no one has looked at the fossil record closely enough, but the jury is certainly still out on this issue. Otherwise, though, a great site with great content - keep up the good work! I think it's perhaps slightly premature to call what's happening at the moment a mass extinction event MME , however if there are intelligent creatures around on Earth in a few million years time perhaps they'll refer to the period we're rapidly moving into as the 'AME' -- Anthropogenic Mass Extinction.
Sounds a lot more serious than 'anthropogenic global warming', does it not? Except for the K-T, most major and minor mass extinctions don't lend themselves to unilateral causes. This may be why they are so rare. However, anthropogenic impacts are not just CO2 or climate related. We may be having an even bigger impact on the nitrogen cycle for example so John Russell may also be correct. We may be changing too many aspects of the Earth system too fast.
Tony 0 0 Steve L at Thingadonta, this may be your best comment here ever, but I have some questions about it. First, you're suggesting that changes due to volcanism over tens of thousands of years are too slow to be compared to what's happening now? Since excess CO2 will remain in the atmosphere for a long, long time, I don't see what you're complaining about.
A dramatic change over the course of centuries will not have less impact than the same amount of change over thousands of years. Second, genera taking 10 million years to recover after mass extinctions -- I suspect that you mean the diversity within genera took a while too develop after the pruning that mass extinctions did to the evolutionary tree. But that's not what reef gaps are. Reef gaps are periods of no reef building. Sure, the biodiversity is reduced, but you don't need all of the species to build a reef -- a limited complement of species should be able to do it.
So apparently conditions not conducive to coraline growth low pH persisted. I need to lean a little less on your excellent synopses and drill through into the citations a bit more. It's not John Cook who's inferred the possibility of an acidification-related extinction but Veron.
So you can take John off your list of physicists making predictions later found wrong. In any case a collection of mostly dead persons are irrelevant to this particular paper. The fact that coral population collapses may occur for reasons other than those Veron surmises says little about his hypothesis. I can think of analogies and so can you, but suffice it say that one failure mode does not exclude another. With reference to past events you say "C02 change is slow", but the change we're concerned with here and now is swift and this is the particul.
I committed the sin of failing to drill through John's synopsis and thus was left with a poor understanding of Veron's case. Now that I've actually scanned Veron's paper, I see he's gone through this subject with substantial attention to detail and makes a pretty thorough accounting for his hypothesis. If you've not read it, you ought to do so. Then it would be interesting to see what you say regarding the paper and its claims specifically, as opposed to remarks about typographic errors in John's post and generalizations about past personalities and events.
Mass extinctions and ocean acidification: But let's stick to the scientific topic at hand, shall we? I understand there is still some debate on the issue. What is the most recent peer revieweed lit on this? However, SciAm referenced a study here as the "definative consensus view" on the issue. A group of 41 researchers have pored over the evidence and decided that—in accordance with the original postulate put forth 30 years ago by a team led by father and son researchers Luis and Walter Alvarez—it was, indeed, a massive asteroid that slammed into Earth, creating Chicxulub Crater on Mexico's Gulf Coast, that killed off many of the species on the planet, including the non-avian dinosaurs.
The review, published online March 4 in Science, evaluated the whole picture, according to Kirk Johnson of the Research and Collections Division at the Denver Museum of Nature and Science and co-author of the paper. And that meant assessing the other theories that have been put forth about what spelled death for the dinosaurs The temporal match between the ejecta layer and the onset of the extinctions and the agreement of ecological patterns in the fossil record with modeled environmental perturbations for example, darkness and cooling lead us to conclude that the Chicxulub impact triggered the mass extinction.
Coal produced after Ma was from different plant species than previously, you also get a lot of red beds at this time indicating hothouse conditions. But my point is, all this took hundreds of thousands- to millions of years of vast amounts of c02 etc from Siberian Traps volcanism-oceans didnt,and probably won't, acidify quickly-ie less than tens of thousands of years? Just because "Event A" happened under "natural conditions" over XXX Ma does not preclude it happening in the short term future. Accelerated release is not contingent upon causation being either "natural" or "human induced".
One would think the idea of positive feedback loops release of the reserves of Co2 and CH4 when we reach the right "tipping point" are crucial to understanding the issue. Increasing concentrations of carbon dioxide in sea water are driving a progressive acidification of the ocean1.
Although the associated changes in the carbonate chemistry of surface and deep waters may adversely affect marine calcifying organisms2, 3, 4, current experiments do not always produce consistent results for a given species5. Ocean sediments record past biological responses to transient greenhouse warming and ocean acidification. During the Palaeocene—Eocene thermal maximum, for example, the biodiversity of benthic calcifying organisms decreased markedly6, 7, whereas extinctions of surface dwellers were very limited8, 9.
Here we use the Earth system model GENIE-1 to simulate and compare directly past and present environmental changes in the marine realm. In our simulation of future ocean conditions, we find an undersaturation with respect to carbonate in the deep ocean that exceeds that experienced during the Palaeocene—Eocene thermal maximum and could endanger calcifying organisms. Furthermore, our simulations show higher rates of environmental change at the surface for the future than the Palaeocene—Eocene thermal maximum, which could potentially challenge the ability of plankton to adapt.
Rate of ocean acidification the fastest in 65 million years Now mind you, the actual paper title is "Past constraints on the vulnerability of marine calcifiers to massive carbon dioxide release" but who am I to deny a blog titled "Desdemona Despair" its little bit of fun? Besides, the more punchy version is after all the title of the press release from U. So paleo data, models, a sexy press release.
What's a rejectionist not to like? Seems unlikely from a level headed publication, if true it's possibly worse given NS has more impact than a single scientist 0 0 Steve L at Or maybe I am. It seems that 35 says that less total CO2 released, but released quickly over a short period of time, cannot have a similar impact as a lot of CO2 released over a longer time period.
I believe this is wrong. To support my assertion I tried to look up a figure I thought it was in Caldiera and Wickett , but my search didn't find a free version of the full paper. My Google search took me to some other interesting stuff. I particularly like the powerpoint presentation fifth down on the list -- lots of references and lots of relevance to the discussion above. Similar but less stuff and more explanation is shown in this pdf. Of particular interest to me in the slide show is the information on other important factors carbonate!
It would be a very long term project for me to study the all the references to permit me to make a good summary. Hopefully someone with more expertise will do it instead. Here is the para I focused on: He posits time periods and natural processes and contrasts by implication possible human interactions with the climate.
That's how I read it. This is how long the geological record generally says it takes, even under extreme scenarios. So I dont know how pro AGW people use the past geological record to scare us abvout short human lifetimes. It's like a biologist scaring us about our rate of speciation.
This is one of the main skeptic arguments -ie the time it takes to change the oceans, warm the planet etc etc add it to the list , and is similar to the arguments in palaeontology and biology over gradual evolution versus punctuated equilibrium.
Earth has entered sixth mass extinction, warn scientists
It's a question of semantics really, eveyone agrees that the rate of evolution can change, but gradualists are very skeptical of any 'jumps' or 'jerks' or 'rapid' rate changes. It also harks back to the days of the catastrophists and the uniformitarians in the 19th century -Darwin was a a uniformatirian and got it wrong with regards to 'mass extinction' events he thought they were just gaps in the fossil record , Cuvier was a catastrophist- like nearly all pro-AGW people, and got it right with to mass extinction events.
But as for mass extinctions, we are talking in most cases, of hundreds of thousands of years. Skeptics, therfore, contend that for somnething like ocean acidification by C02, it will take about that long to do it, which makes current humnan activities regarding ocean acidification, irrelevant. Attempts are currently underway in Austria, Spain and Italy to breed the animals for reintroduction into the wild.
The 20, strong female population is under severe threat by hunters seeking their brown and gold shells. The black rhino has suffered the most drastic decline in total numbers of all rhino species and was officially declared extinct in the wild in However a major conservation effort has seen numbers swell to 5, and now the animals are kept under armed guard. Found on Panama's uninhabited Escudo de Veraguas island, a study found fewer than 80 sloths were still living because of habitat loss by loggers.
Used extensively as a food, and for Chinese medicines, the pangolin has declined by 94 per cent since the s. Exact numbers have been difficult to estimate because the creature is solitary and nocturnal. Accessibility links Skip to article Skip to navigation. Many types of wolves have become extinct including British and Falkland Island varieties Earth has experienced five recognised mass extinctions. Sumatran elephant As more of Sumatran forest becomes converted for agricultural uses, the elephant has faced a critical loss of habitat.
Amur leopard The world's rarest cat is believed to be making a comeback with at least 57 confirmed animals now confirmed Russia. Atlantic goliath grouper Despite the US issuing a moratorium on hunting the big fish in , the animal remains critically endangered. Gulf porpoise The Gulf porpoise is now one of the rarest mammals in the world, with a global population estimated at under in Hawksbill turtle The 20, strong female population is under severe threat by hunters seeking their brown and gold shells. Black rhinoceros The black rhino has suffered the most drastic decline in total numbers of all rhino species and was officially declared extinct in the wild in Pygmy three-toed sloth Found on Panama's uninhabited Escudo de Veraguas island, a study found fewer than 80 sloths were still living because of habitat loss by loggers.