The strongest reasons for doubting the man-made global warming hypothesis come from pre-industrial climate change. During the past 10,000 years, since soon after the end of the last ice age, there have been bigger ups and downs in global temperatures than during the 20th Century. Yet according to the IPCC, citing measurements of gas trapped in polar ice, the concentration of CO2 varied by only about 20 ppm throughout those 10,000 years – less than a quarter of the change during the 20th Century.When I look at the graph, it is pretty clear to me that the recent rise in temperatures is not unusual. The idea that this can only be explained by the rise of CO2 in modern times just doesn't pass the smell test.
So whatever caused the pre-industrial climate changes, it was not CO2. The record is well accounted for, in fact, by (1) a change in the Earth’s attitude in orbit, which brought a gradual cooling to the Northern Hemisphere, and (2) solar variations that superimposed on that trend a succession of warmings and coolings. Yet to offer such natural explanations for past events does not logically falsify the man-made global warming hypothesis, because its supporters say it represents an important new factor in climate change.
If increasing CO2 had no effect whatever on the climate, that might be surprising, but the claim of the hypothesis and its computer models is that the new contribution from man-made greenhouse gases has become the main driver of recent climate change. Implied here is a falsifiable statement, namely that there is something very unusual about the recent warming of the world. That is certainly the sense of many scientific and political pronouncements about global warming.
Here are four ways in which the recent warming might be judged unusual:Data on climate changes of the past 10,000 years are available from various parts of the world, but to make the test as favourable as possible for the man-made warming hypothesis, let’s go to the Arctic. That is where the computer models predict the strongest and most rapid warming, and where the media have publicized repeated claims that Greenland is melting away and the polar bears are drowning.
- by reaching unprecedented temperatures
- by an especially large recent rise
- by an especially rapid recent rise
- by an accelerating rate of rise
Below is a graph using a particularly careful reconstruction of Greenland temperatures during the past 10,000 years, by Bo Vinther of the Niels Bohr Institute in Copenhagen and his colleagues (2009). Ice drilled at the sites called Agassiz and Renland, 1500 km apart on either side of the Greenland ice sheet, provided the data. Anyone who suspects I may misrepresent the results is welcome to compare my graph with Fig. 2c in the 2009 Vinther paper.
Go read the original post. He has a lot more details.
2 comments:
I enjoy reading this kind of stuff, but I have a little trouble with the interpretation of temperature evidence. I also have read that there was a lot of carbon and other gases in the air during certain cycles (from volcanoes) which may have affected the temperatures and climate in a non man made way.. Scientists are looking into a dark hole with flashlights and I am certain that they don't see the entire hole. I also hope that they are true scientists and will change their theories and opinions when new evidence comes to light.
I have another theory: I believe that they have miscalculated the rate of ice and glacier melt and that has thrown off all the other modeling.
My main concern is that we don't fly off the handle, but that we don't sit too long and let the people who are profiting the most tell us that the handle is a perfectly safe place to roost (old joke).
Thomas: I don't buy the "global warming" crisis because it is too simplistic. Greenhouse gases do warm the earth. We would be a frozen ball without greenhouse gases. But there are many other things going on.
As you point out, volcanos emit lots of stuff: CO2, SO2, dust, etc. The SO2 and dust provide nuclei for clouds. If you form high thin clouds they will cool the earth by reflecting light. If you form low thick clouds they will warm the earth by trapping infrared radiation. It isn't simple. Add to this the sun's variation, the changes of the earth's orbit and tilt. Add to this the circulation patterns for air and ocean. Add in biological responses to atmospheric changes. It is very, very complicated.
Here is an excellent article by Luboš Motl, a Czech polymath, who looks at the idea that CO2 created a runaway greenhouse effect on Venus. As you read that, you discover more complexities!
As for you ideas about miscalculating glacial melt, there certainly was a lot of that in the last IPCC report. The IPCC has now admitted its error.
You are right to worry that we don't under-estimate a serious problem, just like we shouldn't over-estimate a serious problem. We need to get it "right". (And getting it right is approximate with lots of wiggle room I would argue. We just have to avoid extremes.)
So I'm big on conservation. I'm big on alternative energy. I'm really big on spending money on basic science. I'm for teaching kiddies that there is this worry looming out there.
But I'm not big on fanaticism, e.g. "the science is decided". No, keep you mind open to alternative possibilities.
I'm not big on committing all resources to "one solution" (especially one that tells the under-developed world they can't have the lifestyles we have and that gives the developed countries a special dispensation to be greedy energy pigs). I'm cynical about "global warming" because I've been through a long series of hysterias: in the 1960s it was "overpopulation" with predictions of mass starvation by the 1980s; in the early 1970s it was the danger that recombinant DNA experiments would let loose a world-wide plague; in the mid-1970s it was "resource exhaustion" with a collapse of industrial society when the oil ran out; in the 1990s it was a fear that robots would suddenly become intelligent and dominate us; in the late 1990s it was a worry that nano technology would let loose self-replicating nanobots that would turn our world into a "gray goo"; in the 2000s it was "the coming plague" such as SARs, bird flu, one of the hemorrhagic fevers, etc...
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