Global Warming Projections Overestimated, Says Black Carbon Study
    By News Staff | November 19th 2008 12:00 AM | 5 comments | Print | E-mail | Track Comments
    A detailed analysis of black carbon, the residue of burned organic matter,  in computer climate models suggests they may be overestimating global warming predictions.  A new Cornell study in Nature Geosciences quantified the amount of black carbon in Australian soils and found that there was far more than expected, said Johannes Lehmann, the paper's lead author and a Cornell professor of biogeochemistry. The survey was the largest of black carbon ever published.

    As a result of global warming, soils are expected to release more carbon dioxide, the major greenhouse gas, into the atmosphere, which, in turn, creates more warming. Climate models try to incorporate these increases of carbon dioxide from soils as the planet warms, but results vary greatly when realistic estimates of black carbon in soils are included in the predictions, the study found.

    Soils include many forms of carbon, including organic carbon from leaf litter and vegetation and black carbon from the burning of organic matter. It takes a few years for organic carbon to decompose, as microbes eat it and convert it to carbon dioxide. But black carbon can take 1,000-2,000 years, on average, to convert to carbon dioxide.

    By entering realistic estimates of stocks of black carbon in soil from two Australian savannas into a computer model that calculates carbon dioxide release from soil, the researchers found that carbon dioxide emissions from soils were reduced by about 20 percent over 100 years, as compared with simulations that did not take black carbon's long shelf life into account.

    The findings are significant because soils are by far the world's largest source of carbon dioxide, producing 10 times more carbon dioxide each year than all the carbon dioxide emissions from human activities combined. Small changes in how carbon emissions from soils are estimated, therefore, can have a large impact.

    "We know from measurements that climate change today is worse than people have predicted," said Lehmann. "But this particular aspect, black carbon's stability in soil, if incorporated in climate models, would actually decrease climate predictions."

    The study quantified the amount of black carbon in 452 Australian soils across two savannas. Black carbon content varied widely, between zero and more than 80 percent, in soils across Australia.

    "It's a mistake to look at soil as one blob of carbon," said Lehmann. "Rather, it has different chemical components with different characteristics. In this way, soil will interact differently to warming based on what's in it."



    ¡ Espero que sí !

    Perhaps Terra Preta production would be a good way of carbon sequestration, too.
    Robert H. Olley / Quondam Physics Department / University of Reading / England
    My husband insists global warming is a myth and all it is is a part of an ice age. He feels there is no evidence that can't be looked at from that perspective. I believe he's wrong but need a really good argument.

    From a science point of view, that's difficult.   Many geologists and climate scientists are knowledgeable about ice cores but not necessarily so astute in statistics.  Projections, past and future, are based on numerical models.  If we take 50 million years and choose 5,000 data points, where and how they are chosen is important.

    What he may be disputing is that there is a carbon dioxide reason behind global warming (is he a Republican?) - but there is an easy physics example to show warming.   Since I was born, the population on the planet has doubled.    Have a party and put 6 people in your living room.   Then double it to 12.   You will note it gets warmer, you may even want to open a door.  Now add in using twice as much energy to feed those extra people, like two ovens or two burners on a stove, and you can see there will be even more added warmth.  Warming can't be a myth but some people trying to raise money made it a political issue.  Al Gore  claiming the oceans would rise 20 feet didn't help things much.

    The good news; 90,000 out of every 100,000 years of world history have been Ice Ages and it's been 12,000 years since the last one.   So we had better be glad there has been 'global warming'!  :)
    The amount of heat produced by 6 billion humans living and eating is small. Even the amount of heat produced by 6 billion humans burning coal, oil, natural gas, wood, etc. is not large compared to the incoming solar radiation.

    However, greenhouse gases have the ability to magnify the sun's effects. My back of the envelope calculation suggests that every MMBtu of coal burned produces 95 kg of CO2. 95 kg of CO2, when converted to ppm, then calculating watts/m2, gets you about 280 MMBtu of lifetime heating by trapping solar heat.

    The basic physics have been known for over 100 years: see Svante Arrhenius and "On the Influence of Carbonic Acid in the Air upon the Temperature of the Ground" (1896, I believe). The hard part is figuring out what the feedbacks are, which determine whether we're going to see 1 or 2 degrees C warming over the next century, or 5 or more. And if you think that 5 degrees C is small-change - well, the last Ice Age was about 5 degrees C colder than today. Try to think about that magnitude change again...

    There is no doubt that the temperature has increased and sea level has risen. Like Hank says, it is hard to prove what causes these changes (other than sea level will rise, however uneven around the globe, due to global warming.) There are also discussions on the models predicting the future development. So there are at least three angles to the question about global warming that too often get confused and the discussions take place based on false premises. False in the sense that people are not discussing the same issues.

    Hank points to a very simple statistical fact. There is a significant increase in number of humans on this planet. In it self the biological mass most likely play a role in the climate models. However, as an astrophysicist I still have to say that the energy represented in human biomass is insignificant compared to the energy from the Sun. I guess I am saying that there are still unanswered questions.

    All this uncertainty about the causes of global warming and climate change IS NO EXCUSE for not stopping wasting our limited energy and polluting.

    Your husband is dead wrong on the question about temperature. It is warmer. But that is perhaps not what he talks about, really...:-)
    Bente Lilja Bye is the author of Lilja - A bouquet of stories about the Earth