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Romanticism undone: Invasive species, global warming taking toll on plants at Thoreau’s Walden Pond

The views expressed are those of the author and are not necessarily those of Scientific American.


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title page of Thoreau's "Walden"Henry David Thoreau famously catalogued the plants around Walden Pond more than 150 years ago, and the information he gathered then is helping to illustrate the effects of invasive species and global warming on the area today.

According to a paper published January 26 in the journal PLoS ONE, climate change has given invasive and nonnative species a leg up in the Walden Pond area, and native species are the losers. (A nonnative species is considered invasive if it has the potential to disperse widely and rapidly, especially within habitats that are minimally maintained by humans. Some nonnative species do not spread quickly enough to qualify as invasive.)

Researchers compared Thoreau’s information with data on temperature and plant populations from this century as well as full information on plant phenology (flowering time, germination, migration and other seasonal activities). They found that the average temperature in Concord, Mass., has increased 2.4 degrees Celsius since Thoreau’s time, and that some nonnative plants have adapted by flowering as much as three weeks earlier than they used to. Some native species, by contrast, were less flexible and have not been able to adjust their flowering times. As a result, their populations have dropped.

"These results demonstrate for the first time that climate change likely plays a direct role in promoting nonnative species success," senior author Charles C. Davis, an assistant professor of organismic and evolutionary biology at Harvard University, said in a prepared statement. "Our research suggests quite decisively that nonnative and invasive species have been the climate change winners. Climate change will lead to an as yet unknown shuffling of species, and it appears that invasive species will become more dominant."

The team didn’t just count the plants to come up with this observation. They also examined "habit, plant height at maturity, leaf mass per area, flower diameter, pollination syndrome and seed weight" to come up with a full picture of the health of the species in the area.

This isn’t the first time that Davis and his colleagues have studied Walden’s plants. Two years ago, they found that 27 percent of the plant species Thoreau recorded from 1851 to 1858 are now locally extinct. Another 36 percent "are so sparse that extinction may be imminent," they wrote in a previous paper. At that time, species like lilies, orchids, violets, roses and dogwoods were shown to have seen the biggest losses.



Image: Cover to Walden by Henry David Thoreau, via
Wikipedia





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  1. 1. pillsburymtn 6:38 pm 02/10/2010

    Global Warming has absolutely nothing to do with the invasive species that are over running Walden’s Pond. Invasive species are being introduced from exotic landscaping features being planted around homes. Furthermore the data supporting the Global Warming hoax has been exposed as being false. Therefore to use a popular term; "Move on"!

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  2. 2. TheSchneid 7:51 pm 02/10/2010

    What’s the big problem with the words "Global Warming". I learned this back in my 1984 Environmental Science class in College. Global Warming is occuring whether you want to dismiss it or not. The question is, "Is it man made, or a natural cycle in the earth’s evolutionary process?" To say Global Warming is a joke is to completely turn your back on years of observation and historical data. The planet is warming up, the polar ice caps are melting, and we’re still listening to a-holes like Rush Limbaugh . Next thing you people are going to start believing is that the earth was created in 7 days. Get real people – Global Warming is Real.

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  3. 3. marcrauch 7:57 pm 02/10/2010

    There is no man-made global warming, it is a fraud, a hoax, an error in judgement; pick the term that best suits you. It does your organization a great disservice to continue on this path. If you want to protect a particular animal species, and stymie normal evolution, that’s fine. But you shouldn’t have to resort to voodoo science to help you.

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  4. 4. ladybugged113 8:11 pm 02/10/2010

    Loss of native species is a great concern. Can anything be done that shifts the balance back in favor of the native species? Perhaps something like adjusting the pH balance of the soil or anything in our means that would give native species their best optimal nutrients to hold their ground and grow their best. Is there enough natural science to know what is optimal for these native species in question? It may be too limiting to consider just climate temperature. If I were to move from Vermont to Florida, I might have a tough time. But if I take off the sweater, use some sunscreen, and get with the vibe, I might just rock, you know? And perhaps, native companion planting of beneficial warmer clime native species may block the onslaught of nonnative species. (I’d want some Vermont honey with me to share the condo in Florida, you know.) Aren’t there plants like stinging nettle and comfrey (or whatever, I don’t know) that are robust and add soil nutrients? Do we (as a community of concerned naturists) know? So, yes, I appreciate your announcement of your problem. It is real. Can we as a community find a remedy? Or, do we just accept that the changes are beyond our control, let nature be nature, live and let die. That is the question being asked. At some point we may have to find a remedy for our own species decline. what of that?

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  5. 5. David Ford 8:23 pm 02/10/2010

    I can’t believe Sci Am is still running articles on GW. I cancelled my subscription several years ago because of an article that was basically a regurgitation of Al Gore’s movie. There are plenty of legitimate challenges to man-made GW that are deserving of publication in Sci Am. If Sci Am is truly "scientific" they will fess up that the science is not settled and publish scientific challenge–not political blather.

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  6. 6. XslyderX 8:30 pm 02/10/2010

    I wonder if the hundreds of people walking around Walden Pond every weekend could have anything to do with native species suffering. It seems everything is being blamed on global warming…despite the fact that climate temps have leveled off, and even declined the last ten years.

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  7. 7. marcrauch 8:55 pm 02/10/2010

    In the argument about global warming, it is axiomatic to infer that "man-made" global warming is the issue, rather than a natural cycle; and this is where the real controversy lies. If the earth is going through a natural warming trend, and it can be indisputably proven that there is a warming trend, so fine, that’s how it is, there is nothing we can do about it.

    But, Mr. The Schneid, the polar ice caps are not in a continuous stage of melting, the earth is not in a warming trend, and Rush Limbaughs voice in this matter is irrelevant compared to the overwhelming scientific consensus that says that man-made global warming is false. Incidentally, I think Limbaughs listenership is down, so you neednt put too much emphasis on whether people are still listening to him.

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  8. 8. marcrauch 8:55 pm 02/10/2010

    In the argument about global warming, it is axiomatic to infer that "man-made" global warming is the issue, rather than a natural cycle; and this is where the real controversy lies. If the earth is going through a natural warming trend, and it can be indisputably proven that there is a warming trend, so fine, that’s how it is, there is nothing we can do about it.

    But, Mr. `The Schneid,’ the polar ice caps are not in a continuous stage of melting, the earth is not in a warming trend, and Rush Limbaugh’s voice in this matter is irrelevant compared to the overwhelming scientific consensus that says that man-made global warming is false. Incidentally, I think Limbaugh’s listenership is down, so you needn’t put too much emphasis on whether people are still listening to him.

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  9. 9. Curious Jack 9:32 pm 02/10/2010

    Plant species are disappearing. Yep it has to be MGW. But wait! Shouldn’t we look at all possible variables? Has there been a change in the population of deer? Deer are much more plentiful than they were 100 years ago. They eat forbs. Flowers, are other leafy plants are food items to deer. Oh, and another thing. Some exotic plant species actually thrive in cool weather. It just seems everyone jumps to conclusions without seriously investigating possible causes.

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  10. 10. smallz0216 10:31 pm 02/10/2010

    Global warming is a JOKE TO MAN KIND!!!!!!!!!!!. Al Gore is making money on it. and it has no sceintific FACT!!!!!! The fact is….that its going to happen whether we influience it or not…look at the facts…………really look at the facts…don’t buy into the BS the is going to make people billions for new ways of making power…its A MARKETING PLOY!!!!! THINK ABOUT IT!

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  11. 11. smallz0216 10:33 pm 02/10/2010

    Global warming is a JOKE TO MAN KIND!!!!!!!!!!!. Al Gore is making money on it. and it has no sceintific FACT!!!!!! The fact is….that its going to happen whether we influience it or not…look at the facts…………really look at the facts…don’t buy into the BS the is going to make people billions for new ways of making power…its A MARKETING PLOY!!!!! THINK ABOUT IT!

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  12. 12. cherock 10:42 pm 02/10/2010

    I’m sure you are all much more informed about this than the Harvard professor and the other thousands of scientists. If I ask you why you believe in God you say that I should have blind faith that he exists, but global warming has data behind it and you dismiss it as nonexistent. You are a walking contradiction.

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  13. 13. boutselis 12:11 am 02/11/2010

    Thoreau was a lot of things. One thing he wasn’t was a botanist .
    What amazes me is a group of people, the climate change priests, are well known for not listening to anyone they feel do not have the proper credentials. but they will listen to some grumpy old writer who lived alone in the woods examining plants. there is no way of knowing if his tabulations are accurate because they had no peer review. They really can not be offered up as scientific evidence. This does not surprise me though. Climate change priests care little for scientific standards.

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  14. 14. boutselis 12:12 am 02/11/2010

    Thoreau was a lot of things. One thing he wasn’t was a botanist .
    What amazes me is a group of people, the climate change priests, are well known for not listening to anyone they feel do not have the proper credentials. but they will listen to some grumpy old writer who lived alone in the woods examining plants. there is no way of knowing if his tabulations are accurate because they had no peer review. They really can not be offered up as scientific evidence. This does not surprise me though. Climate change priests care little for scientific standards.

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  15. 15. kungfu 12:43 am 02/11/2010

    You better look outside idiots. Global warming is the biggest deception ever played on the human race. This has been one of the coolest years in recorded history. Almost every state has set record snow fall and all time low tempatures. I believe GOD is showing you tree huggers how stupid you are. Al Gore owns the company that sells carbon credits. Are you people stupid? God controls the weather not humans. We can’t even predict the weather in 2 weeks little alone in the future. The earth’s tempature goes up and down all the time it’s called seasons Winter,Spring,Summer and fall.

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  16. 16. marcrauch 2:24 am 02/11/2010

    More Proof That Man-Made Global Warming is a Fraud – Direct fron Sen. John Kerry

    Last night, on Larry King’s television show (perhaps the worst interview show ever produced, but that’s something to discuss at a later time), the former Presidential contender John Kerry, and his wife, were Larry’s guests. Larry King asked Kerry about (man-made) global warming. Kerry’s reply was that he just came back from Germany (economic meeting) and that he’s much more concerned about the economy and other issues. The subject of global warming was then dropped.

    If you’ve heard anything that Kerry and his comrades have said over the last few years about global warming, you’d be of the opinion that we (the planet) is doomed if we don’t take immediate corrective action (which includes pissing away trillions of dollars on fake studies and band-aid measures). The projection has been that life, all life, would pretty much come to an end. You’d think that the end of life as we know it would be the most important issue on Kerry’s, or any other political leader’s mind. That extinction is far, far more important than where we rank educationally or economically versus China, India, Japan, etc.

    I mean, if you don’t got life (pardon the poor grammar), who cares if American children can outscore some Chinese kid in a reading contest?

    About two months ago, I wrote an editorial that suggested man-made global warming was a fraud because no government, including our own pabulum-puking-knee-jerk-socialist administration, has taken any significant steps to stop global warming. As I said then, and repeat now, if we are facing extinction within the near future there is no greater issue to address. And if we are not addressing that issue, then it means we are not being so threatened. Consequently, Al Gore, the United Nations, Nancy Pelosi and all the others of their ilk have lied to us. They have wasted our money; they have wasted our time; they have diverted money and efforts from those environmental matters that do matter and that could have made our lives a bit better; and they have brain-washed a generation of our young people.

    Someone ought to send Al Gore a great big jar of petroleum jelly (poetic justice, I think) so that he can put his Nobel award up where it belongs.

    But there is one good piece of good news. In all the years that Larry King has tormented us with his inept interview technique, we finally got a piece of information that we can use, even if Kerry didn’t know that he was surreptitiously admitting that global warming is a fraud.

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  17. 17. stupidisasstupidsays 2:55 am 02/11/2010

    What scary times we live in. EVERYTHING’s politicized!
    ignorant people choose a side and just argue, argue and argue. Three feet of snow caused by global warming — Three feet? Sounds like a good old nor’easter to me. It would convince me more if there was 30ft of snow — maybe — prob not!

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  18. 18. doug 1 7:20 am 02/11/2010

    Yeah…that global warming ruined the glaciers that used to cover walden to a depth of about 2 miles just a few years ago, geologically speaking. Oh, and then that one invasive species, Homo sapiens showed up, shortly thereafter, setting fires to clear the underbrush and selecting preferred species of plants and trees, which they did until their cousins from Europe showed up and began harvesting the old growth which was replaced by relatively young stuff, and then finally Thoreau built his cabing there, and who knows what invasive species and wood cutting he did. Shame on us. We really ought to try salting our opinion with a little objectivity when it comes to natural and cultural history.
    And for the record, human induced climate change has been going on since early man discovered that by setting fires he could drive game, and improve (from the standpoint of his survival) the range. For all we know if humans hadn’t started doing that tens of thousands of years ago, we would once again be under a thick shield of ice as we have been for most of our history as a species.
    If we wish to see a healthy ecosystem, we should of course clean up after ourselves but the hype being generated regarding climate change is largely just that; hype, and proving to be increasingly transparent to those who are genuinely concerned over real issues of environmental degradation. Calling CO2 a toxic gas was the capper that put AGW into the crapper.

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  19. 19. Mojodot 10:20 am 02/11/2010

    It might surprise you to hear that the area you live in is not the center of the universe. Where I live there’s usually 3 feet of snow at this time of the year and right now there is none because the climate is much warmer. Hence why it is called GLOBAL warming and not "local" warming. Although a more suitable name is "climate change" in my opinion.

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  20. 20. downeastdan 10:37 am 02/11/2010

    I don’t believe many of the commentors above are "scientific" anymore than those that think the earth is 6,000 years old and therefore there’s no such thing as "evolution"…a sad retreat from the facts. 98% of climate scientists firmly state that climate change is not a hoax, but a reality. The other 2% probably have their rea$son$…

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  21. 21. Sisko 11:40 am 02/11/2010

    Lots of good laughs when reading some of these blogs.
    There is a great deal of information that shows the earth is warmer today than it was 150 years ago. However, there is no scientific consensus regarding the degree that humans have had on that change.

    Common sense leads one to believe we have had an impact (there are a lot more of us running around than there used to be), but the real debate should be on the specific next steps we should be taking. get down to that and it is a much more interesting discussion.

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  22. 22. PhilJourdan 11:51 am 02/11/2010

    Please source your claims. Please list the 98% that state as you do as well as the source of income for the other 2%.

    I would be very interested to read these facts so I can make an informed decision about your "science".

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  23. 23. binnyblue 11:53 am 02/11/2010

    Shut up!

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  24. 24. binnyblue 11:58 am 02/11/2010

    This person should just shut up about global warming. Yes what is the problem with the words global warming.? It is indeed occuring. Just look at the ice caps and the poor polar bears habitat. You may be correct about landscaping introduction of exotic plants etc. also people tramping around the woods there and swimming with diapers on and such but global warming is happening. What’s the big deal with believing this. It may be cyclical too but that doesn’t mean it isn’t worse at this point and we don’t need to be stewards of the earth.

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  25. 25. TheSchneid 3:13 pm 02/11/2010

    Listen, my arguement was this, I learned about this in Environmental Chemistry Class back in 1984. Global Warming is not "Industry or Economically made" it’s been happening for years. I said in my statement, "Whether it is man made or happening naturally" we must confront it". I’ll give you a few examples of we correcte our mistakes in the past.

    Back in the dust bowl era’s, farmers plowed under their crops after they harvested them. When farm lands went barren due to heat waves and huge dust storms that killed off crops back in the 30′s, scientists came to the resuce, touting farmers shouldn’t plow under their fields until they replant.

    Listen, there are 3 times as many people on the planet then there were 30 years ago. There has to be some damage due to our excess and waste. Look at things like Chernoble, Three Mile Island, The huge copper pit in Butte, Montana, oil spills, etc… The list goes on.

    I don’t think human beings have to change, I think industry has to change. Look at the huge amounts of plastics and foam products used in fast food chains. Even back in the 70′s, enviornmentals challenged corporations from dumping their sewage into rivers and streams.

    Man has to start stepping up to the plate to thwart our destruction of our water resources, energy resources and most importantly our habitat. With out these things, we’re screwed. Don’t fight it, it’s real and it’s been happening now for decades. Once again, whether it’s man made or not, we have to start being more responsible with our resources for the future of man. People who don’t agree are just living for the moment.

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  26. 26. bobwilson 4:22 pm 02/11/2010

    Mr. T lived in the 1700′s little ice age.

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  27. 27. Grasshopper1 7:21 pm 02/11/2010

    Global warming IS real. I believe that it is caused 50% naturally, and 50% by man. Us humans need to do something about it, or else we will be one of the species that die out because of it.

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  28. 28. undercurrent 5:28 am 02/12/2010

    And then what ? I always wondeur why these people who are enthusiastic about non native people coming to our climes in large numbers, don’t want plants to do the same, as if the plant populations that existed in Thoreau’s time had to stay there till the end of times without evolution, which is of course completely anti-darwinian and anti-scientific. Plant evolution is maybe accelerating nowadays, and then what? why is it so bad ? I don’t see the point, and anyway, it’s limited to a few species, I don’t think palm trees are starting to invade the Massachussets ponds! all this hype is laughable!

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  29. 29. focalist 7:21 am 02/12/2010

    Well, Walden is about 15 minutes from my house..and I agree invasive species have done a number on the location. Eurasian Watermilfoil is now in the lake, which means the lake will be effectively dead in a few years unless severe measures are taken (chemical herbicides, dredging). Milfoil makes it into lakes on recreational watercraft- leaf fragments are enough to establish a new plant.

    Walden is about ten miles (if that) from the city of Boston- which means that the park and lake (as it is a state park) gets HEAVY use during summer heat waves, bringing all the loveliness that large numbers of people bring. That being said, the park is kept remarkably pastoral. Still plenty of quiet shoreline to read "On Civil Disobedience"…

    As to whether GW or just good old messy people are to blame for the respeciation of the area.. considering the time frames, I would have to suggest the more likely cause is humans transporting species directly, rather than expansion of natural range due to temperature. I’m not discounting GW, I’m just saying this may be a bit of a reach.

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  30. 30. David Ford 11:15 pm 02/12/2010

    Let’s see– 50% human caused and 50% nature causes. Even if I did buy the fact that human CO2 causes GW (which I don’t), Humans add a littlo over 3% of CO2 emissions to the atmosphere comparred to ~97% mother nature. hmmmm — I just don’t buy the 50-50 "our fault" logic.

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  31. 31. J4zonian 2:42 pm 02/15/2010

    I’m appalled at at the anti-scientific nature of so many of the comments on this SCIENTIFIC American site. Since the overwhelming majority of scientists and scientific studies agree that human-caused climate catastrophe is happening, is dangerous and will, if left unchecked, devastate if not destroy civilization why are we arguing about this? (The number only goes higher as you narrow the polls to scientists in relevant fields, and who actually study the problem.)

    Too many silly and false arguments to respond but just one example: marcrauch: "this is where the real controversy lies"? No, because there is no real controversy; only a manufactured controversy in the corporate-owned media and the minds of poorly-educated, ignorant people. Scientists agree. Corporations who are petrified with terror and rage at the prospect of losing some tiny percentage of their profit disagree. Who you gonna believe?

    Ignore the paid trolls and those who have been fooled by paid trolls and massive oil and coal company campaigns to delay action. Ignore the reality-denying reactionaries. Let’s stick to science on this site.

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  32. 32. lakota2012 6:57 pm 02/15/2010

    pillsburymtn:
    "Global Warming has absolutely nothing to do with the invasive species that are over running Walden’s Pond."
    ———————–

    It sure doesn’t take much for you religious denialists to jump all over any article that mentions global warming.

    What exactly are YOUR CREDENTIALS that could possibly discredit senior author Charles C. Davis, an assistant professor of organismic and evolutionary biology at Harvard University?

    Oh, that’s right, you graduated from the glenn beck school of conspiracy theories proving global warming to be a hoax!

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  33. 33. lakota2012 7:04 pm 02/15/2010

    capriracer351:
    "Give me a break. I just spent the last three hours plowing snow…."
    ————————

    Typical religious denialist, confusing weather with climate, spewing the usual talking points from the cult.

    NASA Aqua Sea Surface Temperatures Support a Very Warm January, 2010
    February 4th, 2010

    The global-average lower tropospheric temperature anomaly soared to +0.72 deg. C in January, 2010. This is the warmest January in the 32-year satellite-based data record.

    http://www.drroyspencer.com/

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  34. 34. lakota2012 7:09 pm 02/15/2010

    David Ford:
    "I can’t believe Sci Am is still running articles on GW. I cancelled my subscription several years ago………."
    ———————–

    …………………..and thought that GW would stop immediately!

    January 2010 UAH Global Temperature Update +0.72 Deg. C
    February 4th, 2010

    The global-average lower tropospheric temperature anomaly soared to +0.72 deg. C in January, 2010. This is the warmest January in the 32-year satellite-based data record.

    This record warmth will seem strange to those who have experienced an unusually cold winter.

    http://www.drroyspencer.com/

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  35. 35. lakota2012 7:35 pm 02/15/2010

    marcrauch:
    "the polar ice caps are not in a continuous stage of melting"
    ——————

    Aaaah, but they are. The Arctic has seen a rapid decline of 11.6% per decade or a total of 34% decline over the past 3 decades from 1979-2009 as far as sea ice extent goes.

    The overall mean winter thickness in 1980 of the Arctic sea ice was 3.63 m compared to a 1.89 m mean thickness in 2008, an astonishing decrease of 1.75 m in thickness.

    "the earth is not in a warming trend"
    ————-

    Of course it is, and even one of the leaders of the denialist cult, dr. roy spencer, shows a steady increase in global temperature on his graph, with the +0.72 C Jan. 2010 temperature anomaly — the warmest January in the 32-year satellite-based data record.
    http://www.drroyspencer.com/latest-global-temperatures/

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  36. 36. lakota2012 7:55 pm 02/15/2010

    "Henry David Thoreau famously catalogued the plants around Walden Pond more than 150 years ago"
    ——————–

    boutselis:
    "Thoreau was a lot of things. One thing he wasn’t was a botanist"
    —————-

    Maybe not, but that certainly didn’t stop him from cataloging the plants around Waldon Pond, and then for senior author Charles C. Davis, an assistant professor of organismic and evolutionary biology at Harvard University to note the differences 150+ years later.

    By you simply spewing, "climate change priests care little for scientific standards," while mocking Thoreau as a "grumpy old writer," proves you are the anti-science misanthrope here!

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  37. 37. lakota2012 8:02 pm 02/15/2010

    kungfu:
    "This has been one of the coolest years in recorded history."
    —————————

    Where’s your proof of that ridiculous statement?

    January 2010 Global Tropospheric Temperature Map
    February 9th, 2010

    Here’s the UAH lower tropospheric temperature anomaly map for January, 2010. As can be seen, Northern Hemispheric land, on a whole, is not as cold as many of us thought.

    NASA Aqua Sea Surface Temperatures Support a Very Warm January, 2010
    February 4th, 2010

    The global-average lower tropospheric temperature anomaly soared to +0.72 deg. C in January, 2010. This is the warmest January in the 32-year satellite-based data record.

    The tropics and Northern and Southern Hemispheres were all well above normal, especially the tropics where El Nino conditions persist.

    http://www.drroyspencer.com/

    Link to this
  38. 38. lakota2012 11:52 am 02/16/2010

    downeastdan:
    I don’t believe many of the commentors above are "scientific" anymore than those that think the earth is 6,000 years old and therefore there’s no such thing as "evolution"…a sad retreat from the facts. 98% of climate scientists firmly state that climate change is not a hoax, but a reality. The other 2% probably have their rea$son$…
    ———————————–

    Exactly! We already know that many denialists have been funded by the manufactured doubt industry, and have just taken their PR campaign from trying to prove no link between smoking and cancer, to new heights while we continue to burn record amounts of fossil fuels.

    As a matter of fact, even 98% of the skeptics agree that global warming exists, and either say it is primarily caused by natural processes, that the cause of global warming is unknown, that global warming will not be significantly negative, or that accuracy of IPCC climate projections is questionable. Only about 2% of the skeptics are true denialists believing that global warming doesn’t exist, or still believe in global cooling after the warmest January in 32 years of satellite records last month.

    Link to this
  39. 39. lakota2012 12:11 pm 02/16/2010

    bobwilson:
    "Mr. T lived in the 1700′s little ice age."
    ——————————

    Actually, Thoreau lived in the 19th century, and besides, it is generally agreed that there were three minima, beginning about 1650, about 1770, and 1850, each separated by intervals of slight warming.

    Link to this
  40. 40. PhilJourdan 10:48 pm 02/18/2010

    Well, the faithful will never buy it, but someone figured out how to test AGW. And the results? http://comments.americanthinker.com/read/42323/540020/page-1.html

    It does not exist. So a lot of accolytes are going to go balistic. I guess they really do not believe in science if they only believe it when it agrees with them,.

    Link to this

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