Humans and environment: more news

About a month ago I posted a link to a story about humans might have increased atmospheric carbon dioxide by enough to cause global climate change thousands of years before industrialization caused the current and ongoing spike in CO2 levels. The mechanism was believed to have been massive burning of forests to clear land for farming. A new paper, however, examines the factors contributing to the rise in CO2 over the last 7000 years. By examining the ratio of two isotopes of carbon in ancient air (trapped in bubbles in ice cores from Antarctica), researchers can figure out, in broad terms, the origin of atmospheric CO2. The results of a recent analysis of nearly 200 samples indicate that human land use played only a small part, and that the pre-industrial rise was mostly natural (due to a natural increase of vegetation after the ice age ended and the effect this had on ocean chemistry). This news story from Science magazine has the details.

This is particularly interesting in the context of a new framework for evaluating the impact of humans on their planet. A team of scientists published an article in Nature this week describing the environmental limits that mark out a “safe planetary operating space.” They identified nine factors (one of which is biological diversity, so at least it’s not entirely about a safe operating space for humans alone). Check out Nature‘s Planetary Boundaries special feature. It looks like at least some of the content is available even to non-subscribers. However, in case that changes at some point, here’s a story from Science Daily.

And while we’re on the topic of the effect we have on our planet, this week New Scientist also published a series of articles on population, at least some of which appear to be available to all.


  1. Hi Ian–Right, the more recent story indicates that pre-industrial human impact on CO2 levels was fairly small, in contrast to the earlier story.

    Regarding the influence of post-Ice-Age vegetation, it seems to be a bit mixed. As best I can gather from the abstract of the paper in Nature, a decrease in CO2 in the early Holocene is partly the result of carbon uptake by plants, as you suggest. However, a CO2 increase in the later Holocene is due partly to “carbonate compensation of earlier land-biosphere uptake.” (The abstract is at

    And yes, I’ve read Collapse–I’m a big Jared Diamond fan and I appreciate his cautious optimism (although these days it’s easier to feel more caution than optimism). Guns, Germs, and Steel was one of the most enjoyable reading experiences I’ve ever had.

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