Pre-Industrial Climate Debate Warms Up
As reported last month in Nature,
Scientists have come up with new evidence in support of the controversial idea that humanity’s influence on climate began not during the industrial revolution, but thousands of years ago.
Now, in a guest post at Real Climate, William Ruddiman summarizes the new evidence that will appear in an upcoming special issue of the journal, Holocene. He writes:
Arguably, the most significant new insight emerging from this issue comes from several papers that converge on a view of pre-industrial land use that is very different from the one that has prevailed until recently. Most previous modeling simulations relied on the simplifying assumption that per-capita clearance and cultivation remained small and nearly constant during the late Holocene, but historical and archeological data now reveal much larger earlier per-capita land use than used in these models.
Why is this important? As a recent article in Science News (previewing some of the new research) puts it:
Climate scientists often select 1850 as the putative start of the industrial revolution. But the world in 1850 was not a pristine globe untouched by human hands.
Ruddiman acknowledges in his Real Climate post that debate on the early anthropocene hypothesis is far from over. Still, he writes:
the new evidence points the way toward three avenues of exploration that promise to deliver a resolution of this issue: (1) more thorough investigation of historical records of pre-industrial land use; (2) additional archeological work to fill in gaps in spatial/temporal coverage of the spread of agriculture, and (3) further modeling work to transform historical and archeological data into quantitative estimates of the effects of early agriculture on atmospheric CO2 and CH4 concentrations.
It’s pretty neat that environmental history and archaeology–two disciplines of great interest to me–are being seen as increasingly important contributors to climate science debates.
“Climate scientists often select 1850 as the putative start of the industrial revolution. But the world in 1850 was not a pristine globe untouched by human hands.”
Non-sequitur, Keith. Or straw man. William Blake wrote about “dark Satanic mills” half a century before 1850. I have any number of books from the past few decades that discuss air pollution in London in the 13th century from burning coal (e.g., Edward I in 1272 threatening coal burners with torture and death) and the fact that heavy metal contamination from ancient Roman metal smelting can be clearly seen in Greenland ice cores.
E.O. Wilson and Jared Diamond have written about environmental devastation in Pacific islands caused by Polynesian civilizations (Diamond most famously about Easter Island and Wilson about loss of Hawai’ian biodiversity when the first human settlers brought invasive species), and there’s a large literature as well about the environmental impacts of indigenous civilizations in North and Central America.
So there’s nothing new in saying that the world wasn’t pristine before the coal revolution. Ruddiman’s hypothesis is very interesting for scientific reasons, but it isn’t relevant to contemporary environmental politics and I doubt that it’s very relevant either to the science of climate change due to fossil fuel consumption.
I think that one other interesting aspect that may arise from this work is a greater appreciation of non-European prehistory. Most of us look at the past through a decidedly European oriented lens in which many past civilizations, such as those on the American continents, are largely ignored.
I left something relevant out of my previous comment: Despite the fact that the world wasn’t “pristine” before 1850, there’s a good reason to pick a date in the mid 19th century as the start of industrial anthropogenic interference with climate: that’s when burning fossil fuels started to be a large enough effect to strongly perturb the composition of the atmosphere. Since fossil fuel consumption since that time has been so much greater than all other forms of anthropogenic forcing combined, it’s relevant to mark the mid-19th century as a point where the game changed dramatically. Nothing in Ruddiman’s work challenges this.
Ruddiman is talking about an increase of 24-40 ppm CO2 over the course of 5000 years, compared to an increase of more than 100 ppm since 1850.
Carbon dioxide is not the only anthropogenic contribution. Early farmers may have influenced albedo, transpiration (water availability) and methane (cattle and rice farming). For that matter, pre-farming techniques such as burning may well have impacted climate.
Jonathan (1),
You’re being a literalist with that quote I used from Science News. Whats’ being referred to there is a cultural lens/mindset that really only has been slowly abandoned in the last few decades.
Additionally, ever since publication of George Perkins Marsh’s Man and Nature, many people have labored under the notion that nature exists apart from humans. That duality, combined with the myth of Pre-columbian eden (and minimal ancient human footprint), is slowly melting away.
I disagree with your assertion that Ruddiman’s assertion is not relevant to contemporary env politics and even the larger climate debate. But it’s better for me to devote a future post why I think this.
Keith. I didn’t mean to be a silly literalist. I think you and I agree and are putting our emphasis differently: You write, “there is a cultural lens/mindset that really only has been slowly abandoned in the last few decades.” I agree that there’s a been a real change over the past few decades in the way people look at preindustrial environmental impacts but in my view that battle is largely over whereas you seem to see it as still underway.
I do look forward to your thoughts about why protohistorical environmental impacts are relevant to contemporary politics.
KK: Today, I couldn’t post a comment from iPhone, although it works fine with other mobile sites, You may want top check.
I ma be able to clear up some misapprehensions for Jonathan.
1) Bill demonstrably has zero doubt about the Industrial revolution warming. Among other things, he created the panel for the GSA, which wrote their statement:
http://www.geosociety.org/positions/roster/pos10.htm
http://www.geosociety.org/positions/pos10_climate.pdf
2) See:
http://www.skepticalscience.com/fixednum.php
As a quick scan, Bill’s hypotheses likely argue *against* (bad) memes 2, 21, 31, 32, 36, 43, 69, 85, 111, 163. That is, he argues that humans have long affected the climate … even if we;re affecting it much more strongly since the IR started. While it is nontrivial to analyze, given the long residence time of CO2 in the atmosphere (and the stronger effects of CH4 while it is resident), a relatively small difference of CO2/CH4 over thousands of years cannot be ignored, just as a a big change in a few years cannot.
When Bill’s PPP came out, at first, some of the usual climate anti-science folks welcomed Bill’s work … because they didn’t understand it. I think they late realized their mistake.
3) However, while people have long understood that pre-1850 wasn’t pristine, there has been continuing arguments pro/con on whether or not humans could have a had a significant effect on global climate itself. People have to do the hard work of bounding uncertainties, to show that the effects seen lie outside the natural variabilities. that seems to be happening, but a few scientists seem to remain deadset against it. Again, it is not an argument pristine-vs-non-pristine, but of “how *much* effect could/did humans have, and when?”
Bill is in essence saying that human effects held off the usual long slow slide towards the next ice age, and kept temperatures within a fairly narrow range … for which our agriculture and infrastructure have been tuned … and which we are about to leave at the high side, beyond any experienced during civilized history. For thousands of years, we have been living with a global thermostat, as human emissions more-or-less balanced decrease in solar insolation @ 60N.
4) This is absolutely relevant right now.
a) Climate models not only include physics, but use paleoclimate data to bound uncertainties. In particular, “natural climate variability” at various timescales and “climate sensitivity” are fairly relevant items …
b) For a given emissions scenario, narrower uncertainty bounds amount to differences of Trillions of dollars of cost over the next century, hence are quite relevant to policy.
c) Bill didn’t go into the additional hypothesis regarding plague-induced CO2 jiggles, but that will be seen in another article in The Holocene by Nevle, et al; that isn’t onliine yet. That’s especially exciting, as it may help explain the CO2 plunge ~1600AD, *before* the Maunder Minimum.
http://i39.tinypic.com/if0m5g.jpg
Hopefully, Bill will post again when that come out.
Just using guesstimated World Population figures would pretty much dictate that humans didn’t begin to have much of an impact until the 14th Century when we started cranking out the second billion.
http://bixby.berkeley.edu/wp-content/uploads/2009/03/current-pop-jpeg.JPG
Doubt the “human” contribution was much more than a few huge grass fires in Asia or N.America, or a Chinese civil war or two (or a volcano or two). Can’t see that we really mattered very much for most of the past 6 million years.
Look up the “pioneer effect” The clearing of the Americas and Australia for agriculture had significant effects pre 1850.
@John Mashey: Nice, informative comment, which provides much food for thought. I appreciate the effort you put into trying to clear things up for me.
If I gave the impression that I thought the Ruddiman hypothesis conflicted with contemporary AGW or that Ruddiman doubted contemporary AGW, that was unintentional and I’ll offer an apology to Ruddiman if I have given anyone that impression. I have read a good deal of his work and taught from his textbook on climate, and I agree with you that he’s utterly clear that contemporary anthropogenic warming is real and dangerous.
I have some reactions to your comments, but I can’t edit them down to a manageable size, so I’ll wait until I can distil them better before commenting further.
re: #10
Thanks. As usual, it takes more work to make something shorter.
In any case, all this is a great example of real science at work, with dueling papers trying to illuminate uncertainties. As KK notes, environmental history & archaeology are playing bigger parts. The really tricky part is the huge dispersion of the relevant sources across the literature.