Rapid warming boosted ancient rainforest
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By Joseph Milton
Most scientists have assumed that, as carbon dioxide levels increase and the Earth warms, plant species diversity in the rainforests will start to dwindle, with plants unable to adapt to the heat. But a new study suggests that the opposite may be true. In the past, rising atmospheric carbon dioxide and higher temperatures actually drove the evolution of far greater numbers of new rainforest plant species than were wiped out.
But don't trade in your electric car for a gas-guzzler just yet--if rainfall drops as temperatures rise, or if they rise too rapidly, the outcome for rainforest diversity could be much less positive.
For clues to how rainforest diversity will be affected by increasing atmospheric carbon dioxide and the corresponding rise in temperatures, Carlos Jaramillo, a palaeobiologist at the Smithsonian Tropical Research Institute in Panama, and his colleagues decided to look at what happened during similar conditions in the past.
One such episode in Earth's history occurred 56.3 million years ago and is called the Palaeocene-Eocene Thermal Maximum (PETM). Within 10,000-20,000 years, the world warmed by 3-5 degrees Celsius and atmospheric carbon dioxide doubled to around two and a half times the levels we see today. These unusually warm conditions lasted for around 200,000 years.
Pollen clues
To find out how this ancient climate change affected rainforest plants, Jaramillo and his team analyzed fossilized pollen trapped in rock cores from rainforests in Colombia and Venezuela. They spent seven years locating appropriate sites and taking samples, then used a battery of dating techniques to ensure that they were examining cores formed before, during and after the thermal maximum--a relatively narrow time window in geological terms. The results were published November 12 in Science.
Although some plant species disappeared, many more new species arose. That included entire families, suggesting that the increased temperatures and carbon dioxide levels actually boosted biodiversity. "What we found was exactly the opposite of what we were expecting," says Jaramillo. "The diversity of the tropical forest increased really fast over a very short amount of time."
The pollen fossil record shows that some important plant families, such as Myrtaceae, which includes eucalyptus, and Passifloraceae--the passion flowers--made their first appearance during the thermal maximum. The tropics have remained the most species-diverse area of the world ever since.
This might sound like good news for the rainforest in the face of contemporary climate change. However, Guy Harrington, a palaeobiologist at the University of Birmingham, UK, warns that any positive effects on plant diversity could be canceled out if temperatures rise too quickly for plants to adapt. "It's the rate--how fast you're turning up the heater--that's the most important thing," he says.
The availability of water could be critical too, he adds. There was no shortage of water during the PETM, but the effects of future climate change on rainfall in the tropics are uncertain.
The beneficial effects of a hotter and more carbon dioxide-rich world may also be limited to the tropics. Harrington has studied fossil deposits from the period in North America, and says that many native species died out there as temperatures rose. He adds that higher latitudes are more likely to suffer from extreme conditions or lack of water.
Despite the caveats, Harrington fears that "uninformed climate skeptics will probably use this as evidence" to say that action on global warming isn't necessary. Jaramillo agrees: "Of course I'm worried some people will look at this and say 'we shouldn't care about global warming'," he says, "but this is what the fossil record is telling us."
Jaramillo believes that there is a more pressing threat to the diversity of tropical rainforests. "Deforestation is the real enemy," he says, "not the increase in temperature and carbon dioxide."
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13 Comments
Add CommentThis Article is interesting. It appears that the person who was quoted at the end of the Article is trying to engage in damage control. He is worried that the news that warmer temperatures in the past resulted in more species, not less.
Reply | Report Abuse | Link to thisThe North American record is less clear also.
I am saddened when research results in these sorts of blatantly political exercises in "Spin". As a long time observer of the science reported here, My conclusion is that the research is not finished.
I have seen a great deal of the evidence cherry picked, or outright fabricated by both sides. Politics destroys real science. We sorely need openness and peer review. What passes for peer review in this field is called character assassination when it happens in other places.
Give the evidence, and your conclusions, and let the evidence speak.
What concerns me most is that many people just want to some action be taken to address global warming. I fear that the best intended but unproven actions can produce even more unexpected damage than taking no action.
Reply | Report Abuse | Link to thisJust for example, if atmospheric co2 is improperly sequestered in minerals at necessary large scales, catastrophic releases triggered by rainfall could suddenly produce cataclysmic climate changes.
We've been running uncontrolled climate experiments for a couple of hundred years. The last thing we need is more dramatic unexpected results.
Isn't it a bit of a broad stroke to label all "human caused global warming disaster skeptics with the same brush of UNINFORMED?
Reply | Report Abuse | Link to thisHere are a FEW of the INFORMED skeptics:
Robert M. Carter, geologist, researcher at the Marine Geophysical Laboratory at James Cook University in Australia;
Robert C. Balling, Jr., a professor of geography at Arizona State University;
Antonino Zichichi, emeritus professor of nuclear physics at the University of Bologna and president of the World Federation of Scientists
To summarize, Jarmello and his team, studying fossil rainforests in Colombia and Venezuela during the PETM found a net increase in floral biodiversity whereas Harrington's studies of fossil deposits from the period in North America indicates that many native species died out there as temperatures rose, especially at higher latitudes.
Reply | Report Abuse | Link to thisWikipedia indicates that there must have been forests covering most of the Earth, from pole to pole, and that tropical rain forests extended as far North as Alaska.
Both the findings of a net increase in floral biodiversity in the tropics and the 'loss' of many previously established species in North America can easily be satisfied in a transition to tropical species throughout the Arctic region.
The spread of tropical forests might not have been such a bad thing, but it certainly would have required adaptability of surviving species. Of course, there no humans present at the time to engage in tactical nuclear conflicts over changes in the geopolitical availability of natural resources, for example.
It sounds like, from the article, that the higher the CO2 gets, the better it is for the planet. I agree with that. The mistake the article made, and it seems everyone else is making...it's not the CO2 that is causing the rapid increase in temperatures today, plunging species into extinction, or global warming.... For diversity and the start of new species, we need CO2 increases. What is causing the rapid and out of control increase in temperatures today, and caused by humankind is the CO1 (carbon monoxide); the poison gas that comes from burning fossil fuels in power plants and automobiles. If you stopped the production of CO1 (carbon monoxide) today, probably in less than ten years the atmosphere would be almost back to normal and our normal production of CO2 would continue. It is obvious and it has been obvious throughout our history that we need CO2 production that comes from the great number of animals on this planet to make our vegetation healthier and more productive and it is the vegetation that makes us healthier and more productive.
Reply | Report Abuse | Link to thisJust by converting over to electric cars and non-fossil fuel power production as quickly as possible, we can save ourselves and our planet.
James, you offer an almost obvious and sensible observation. Carbon monoxide is the inconsistency and harmful to all life unlike carbon dioxide. The resiliency of the earth if this is addressed in a timely manner makes this a very attractive point of focus with measurable results.
Reply | Report Abuse | Link to thisSo obvious that scientists don't seem to be talking about it at all, although if you can cite references I'll gladly cede the point. This just feels like more of the same off the cuff ranting that frequently pops up in climate discussion. I'm endlessly amused by the average Joe characters in these forums that make sweeping generalizations and manage to convince each other that they are better equipped to deal with our issues than a legion of trained experts.
Reply | Report Abuse | Link to thisSeriously, though. CO2 as a gas is indeed good - for plants. But you know what, plants don't need nearly as much as has been made available to them right now. For the time being the planet's natural carbon sink is out of balance with its supply, and because CO2 is a heat trapping gas, we're in the process of creating a positive feedback system. Also, notice the section of the article that referred to the importance of how quickly the changes take place. For the PETM, it took between ten and twenty thousand years for the average temperature to rise three to five degrees. We are likely to accomplish it in two hundred years if we remain at our present level of output. That's 1% of the time it took historically. That's scary.
I agree and want to point out that many people seem to be making comparisons of past climate changes to current ones.
Reply | Report Abuse | Link to thisMost of the best paleoclimatological data (deep ice cores and sediment deposits among others) show big changes in climate (from snowball Earth to hothouse Earth) that were completely natural but took large timescales.
There have been occasional rapid changes, like when the ice dam over North America broke and basically overnight changed the global thermohaline ocean circulation but that seems to be the more rare and less extensive event type.
Anyway, my point is that today's changes are happening in a relative geological eyeblink and comparing how many species can survive and thrive big changes just because the end condition is similar to some past epoch of the Earth may be very misleading to some. Who knows how our experiment will turn out? There is no precedent or truly comparable event.
The article states that the rate of change is critical. It does not state the timeline over which the new species evolved. Can we assume tens of thousands of years, or more? And can we assume that the current changes in our atmosphere occurring over a couple of hundred years is WAY too fast for plants to adapt and or evolve? Back to square one folks, will we, when will we, and how will we at least SLOW DOWN the changes we are making to every ecosystem on our planet? From TS Elliot's The Hollow Men, Between the idea and the reality, Between the motion and the act, Falls the Shadow. This is the way the world ends, not with a bang, but a whimper... and we, the hollow men and women, will also be panting.
Reply | Report Abuse | Link to thisPlease bear in mind that using diversity as the sole measure of the effects of climate change does not tell the entire story. The northern boreal forest is certainly not as diverse as the tropics. However, that lack of diversity does not prevent that biome from covering a significant part of our northern land masses. Further it is not quite accurate to say that North American species came extinct unless you are speaking of those that could only survive in the high arctic. During the PETM and the Eminem-sangamonian interglacial for that matter, all the major land biomes expanded at the expense of the high arctic. In other words, the tropics expanded, the sub tropical deserts expanded, the temperate zones expanded; all in a northerly (or southerly)direction. True species did not live at the same location on the planet as they had been prior to the warming, they moved as their ecosystems expanded towards the poles.
Reply | Report Abuse | Link to thisThe benefit of this research is that it serves to buffer some of the more extreme claims of the proGW side. These extreme arguments alienate more of the general public than they attract. Unfortunately public acceptance of science is slow even in the best conditions (unless it is an “i” something). In a world of sound bites where fear and anxiety are being dumped on people daily, at some point they say enough and for sanity sake they ignore the message at best or at worst become hostile to it. Contrary to popular opinion, fear is a poor motivator of behavior change particularly if the threat is amorphous and the claims being made appear unreasonable. With or without GW there are ample reasons to move away from a monoculture of energy generation. The emphasis of the debate over energy should be on that message with science playing a supporting role.
On a side note, several commentators mentioned the perceived panacea of electric cars. Technical issues aside, Electric vehicle only reduce CO2 emissions if and only if you live in an area that is not using fossil fuel to generate electricity! Check your laws of thermodynamics; every conversion from one form to another entails a net loss. Two or so months ago Sci. Amer. published a map of the US show the regions where electrics would be a net reduction, a neutral or a net increase regarding CO2 emissions. Unfortunately the bulk of our populations live in areas where they are neutral to a frank negative. If you live east of Minnesota and north of the Tennessee, the worst action you could take regarding you personal CO2 emissions is to buy an electric car.
Maybe I'll have to give up my worst case scenario of Earth becoming another Venus, and the final result may be many new and exotic species, but this doesn't tell us it will be any better for conscious beings in the short run. Evolution happens fastest in troubled times, and we're likely to experience some of it soon. I probably won't get to see many newly successful species, so part of me is glad I was born somewhat before the "boomers".
Reply | Report Abuse | Link to thisI hate to be a bit of a contrarian but some of the concerns regarding rates of climatic change and rates of speciation are abit overstated. This planet has experienced changes climatic changes that took place over long periods and some that took place essentially instantaneously in geologic time scales. In all cases, life came through these changes just fine. Granted the question of whether we humans will make it through is open for debate. So please differentiate your arguments between life surviving our changes and us surviving our changes. Second, the process of speciation is a strange animal; one that we are not very good at determining. By definition, in a planet where the majority of niches are already occupied, one species must be displaced or due to its extinction another species expands into the area once occupied. At this point you are at diversity-1. If that expanded becomes isolated, the process of speciation will begin. However, there were never any voids in the ecosystem. Recently we have discovered that what we classified as species under the Linnean system have not proven to be so. Polar bears are just white phase grizzlies. This underscores our limitations in determining when a species actually comes into existence. Consequently biodiversity is a reflection of our definitions as much as it is due to the state of the real world. When considering the ramifications of speciation and extinction I am heartened by paleontologist Jack Horner's observation "things die...animals go extinct...and its OK.
Reply | Report Abuse | Link to thisThis has been a very positive discussion - congratulations!
Reply | Report Abuse | Link to thisWhile the suddenness of potential changes that are likely to occur over the next ~50-100 years (regardless of any future change in co2 emissions, due to the thermal momentum of Earth's enormous masses) may distinguish upcoming climate changes from those of past periods, more immediate adjustments will most likely be made through species migrations (including flora) rather than only through slower evolutionary genetic adaptations.
The one 'organism' that may have never been tested in these extreme conditions is the modern technological society supporting the human overpopulation of planet Earth. It is we that are precariously balanced on the precipice of our own collapse. Perhaps our technological capabilities can sustain us.
I hate to be pessimistic, but the support infrastructure provided by our cities and agricultural facilities can't be physically moved away from the equator and our populations can't migrate without devastating disruption. I'll be gone by then, but I'm worried about my existing children and grandchildren and hope that a viable human population can survive.
They say that 70,000 years ago sudden climate change resulting from the Toga supervolcano eruption diminished the global human population from perhaps 1 million to a few thousand people. It is those survivors that, over tens of thousands of years, developed abstract reasoning and symbolic communications capabilities, eventually producing the current technological civilization. I hope that some can now survive the deaths of billions, and that they can improve on this model.