If your library has a copy of the 1991 IPPC First Assessment Report, you should take a look at the section on historical climate. It has a graph of temperature reconstruction for the last 1,000 years or so. It corresponds to what you find in every other standard work before 2000. Like this one:
(You can’t get the 1991 IPCC report online, although you can see subsequent reports).
Now take a look at the IPCC Third Assessment Report from 2001 (the “TAR”). In chapter 2, on page 134 you see this temperature reconstruction:
Whew! How did that happen?
It’s possible that this is science progress – new research uncovers new data and overturns old paradigms. Decades of work and hundreds of peer-reviewed papers did produce the consensus you see in the first graph. Maybe they were wrong.
This isn’t the place to write about the Hockey Stick debate, as its known. You can read about it for days – weeks even – and honestly, it’s probably worth every minute.
One place to start is with the Wegman report, one cherry-picked extract: “Overall, our committee believes that Mann’s assessments that the decade of the 1990s was the hottest decade of the millennium and that 1998 was the hottest year of the millennium cannot be supported by his analysis.”
Edward J. Wegman analyzed the Mann et all 1998 paper – the paper upon which the IPCC based its new temperature reconstruction. But don’t take my cherry-picked word for it, read the whole thing for your yourself, make up your own mind.
And while we are on that subject, Wegman might well have great stature in the science community, but you have to judge for yourself, after all he’s not infallible. Other links for the hockey stick debate: the wonderful people at Real Climate, “Climate Science from Climate Scientists“; and Climate Audit (the link is a new mirror site, it just got overloaded due to popularity). Real Climate includes Michael Mann – no, not the director of Heat with Pacino and De Niro – he’s the author of the controversial 1998 paper that started the whole debate. And Climate Audit is run by Steve McIntyre, whose joint investigation with Ross McKitrick got the whole debate finally kicked into the hands of the NAS and Edward J. Wegman.
The history of our climate has a huge impact on the science of climate.
Here’s a climate reconstruction of the last 1,000,000 years:
Here’s a comment from this reference work (Holmes) in respect of these reconstructions:
The recent past has known dramatic and fundamental changes of climate and environment which have affected the whole Earth, from the top of the highest mountains to the bottom of the deepest oceans. Morever, many of these changes have occurred at surprising speeds. Although the Earth’s environment may now be changing in response to human activities, even without them, rapid and dramatic changes in the environment would occur quite naturally.
The earth’s recent history and its implications will be an important theme of this blog.
A note for those new to temperature history. Proper temperature measurement on a worldwide basis only goes back into the second half of the 19th century. And the longest temperature series (from Central England) only goes back to the mid 17th century. So all attempts to measure the past history of our climate rely on proxies. Temperature proxies include ice core data and tree rings. Proxies aren’t like perfect thermometers and the further you go back the more difficult the analysis becomes.
In the cause of science and the spirit of balance I think the IPCC should display the million year temperature reconstruction prominently in its next assessment report.
Sharp-eyed observers will think this unlikely to happen.