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8,000 years of Man Made Global Warming (5 posts)

  1. chrisc

    This is an interesting PDF on the effects on the climate that deforestation and other human activity has caused in the last 8,000 years:

    Abstract. The anthropogenic era is generally thought to have begun 150 to 200 years ago, when the industrial revolution began producing CO2 and CH4 at rates sufficient to alter their compositions in the atmosphere. A different hypothesis is posed here: anthropogenic emissions of these gases first altered atmospheric concentrations thousands of years ago. This hypothesis is based on three arguments. (1) Cyclic variations in CO2 and CH4 driven by Earth-orbital changes during the last 350,000 years predict decreases throughout the Holocene, but the CO2 trend began an anomalous increase 8000 years ago, and the CH4 trend did so 5000 years ago. (2) Published explanations for these mid- to late-Holocene gas increases based on natural forcing can be rejected based on paleocli- matic evidence. (3) A wide array of archeological, cultural, historical and geologic evidence points to viable explanations tied to anthropogenic changes resulting from early agriculture in Eurasia, including the start of forest clearance by 8000 years ago and of rice irrigation by 5000 years ago. In recent millennia, the estimated warming caused by these early gas emissions reached a global-mean value of ∼0.8 ◦ C and roughly 2 ◦ C at high latitudes, large enough to have stopped a glaciation of northeastern Canada predicted by two kinds of climatic models. CO2 oscillations of ∼10 ppm in the last 1000 years are too large to be explained by external (solar-volcanic) forcing, but they can be explained by outbreaks of bubonic plague that caused historically documented farm abandonment in western Eurasia. Forest regrowth on abandoned farms sequestered enough carbon to account for the observed CO2 decreases. Plague-driven CO2 changes were also a significant causal factor in temperature changes during the Little Ice Age (1300–1900 AD).

    I found it via a comment on this thread:

    Posted 9 years ago #
  2. chrisc

    Humans started causing global warming 5,000 years ago

    Global warming didn't start with the industrial revolution, but began 5,000 to 8,000 years ago with large-scale agriculture in Asia and extensive deforestation in Europe, according to new research by University of Wisconsin-Madison scientists.

    Using powerful supercomputers and advanced climate models, the researchers concluded that methane and carbon dioxide - the building blocks of global warming - began rising with the introduction of rice cultivation and large-scale tree removal.

    "I think that the take-home message is that this hypothesis shows that climates are extremely sensitive to small variations in greenhouse gases," said Steve Vavrus, a climatologist at UW's Center for Climatic Research.

    Vavrus and his colleagues John Kutzbach and Gwenäelle Philippon were to discuss their research today at a meeting of the American Geophysical Union in San Francisco.

    The work of the UW team also shows that the build-up of greenhouse gases over thousands of years has prevented the start of a new glacial age.


    Posted 9 years ago #
  3. chrisc

    Did Early Global Warming Divert A New Glacial Age?

    ScienceDaily (Dec. 18, 2008) — The common wisdom is that the invention of the steam engine and the advent of the coal-fueled industrial age marked the beginning of human influence on global climate.

    But gathering physical evidence, backed by powerful simulations on the world's most advanced computer climate models, is reshaping that view and lending strong support to the radical idea that human-induced climate change began not 200 years ago, but thousands of years ago with the onset of large-scale agriculture in Asia and extensive deforestation in Europe.

    What's more, according to the same computer simulations, the cumulative effect of thousands of years of human influence on climate is preventing the world from entering a new glacial age, altering a clockwork rhythm of periodic cooling of the planet that extends back more than a million years.

    "This challenges the paradigm that things began changing with the Industrial Revolution," says Stephen Vavrus, a climatologist at the University of Wisconsin-Madison's Center for Climatic Research and the Nelson Institute for Environmental Studies. "If you think about even a small rate of increase over a long period of time, it becomes important."


    Posted 9 years ago #
  4. chrisc

    BBC - Radio 4 - Frontiers 31/05/2006 -- Anthropogenic Climate Change

    In this week's episode of Frontiers, Peter Evans meets climatologist Professor Bill Ruddiman whose views about climate change have divided scientific opinion.

    Bill's argument is that 8000 years ago, Neolithic farming produced major emissions of carbon dioxide and methane. Land clearance and rice cultivation led to such large amounts of carbon dioxide and methane being released into the atmosphere that they countered the natural decreases that would otherwise have happened.

    RealAudio of this show here:

    Posted 9 years ago #
  5. truthmod

    If the effects of the relatively small and "primitive" population of humans thousands of years ago was enough to effect the climate, it's pretty scary to think of the the drastic effects that modern humans are wreaking...

    And yet some people still think we're too small to change something as big as the planet.

    Posted 9 years ago #


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