Of all people involved in the promotion of the Hockey Stick, Sir John Houghton, head of the IPCC is probably the chief champion of MBH98 and MBH99 as the "scientific consensus" of how the global climate changed in the last millenium.
Here’s Sir John in front of that famous graph
Referring to the Hockey Stick, he lectured:
Global warming is a second and a more important example of this global pollution [other than the smog found in 19th Century London and most cities]. Carbon dioxide that I cause to be emitted, because I drive my car or use electricity or in many other ways, enters the atmosphere, and rapidly spreads around the whole atmosphere, much of it remaining in the atmosphere for 100 years or more. Now, because carbon dioxide is a greenhouse gas, it causes the average global temperature to increase, significantly affecting the climate. So everybody in the world is affected.
But you will see that the nature and rapidity of the change in temperature over the 20th Century is very different from that over the previous 1000 years. In particular the recent years have been the warmest over that entire period. 1998 was the warmest year in the global instrumental record, and a more striking statistic is that each of the first eight months of 1998 was the warmest of those months in the instrumental record – suggesting that the earth really is warming up.
So you see that Sir John links the results presented by the Mann Hockey Stick as key proof that
- the Earth is warming due to build-up of greenhouse gases, principally carbon dioxide
- 1998 is the "warmest year of the millenium"
- the 20th Century warming is "very different from that over the previous 1000 years"
- that the change in climate is predominently caused by mankind.
Speaking in Shanghai and being pictured above in front of the Hockey Stick, Sir John opined:
prised at how little it turns out we need to do to the climate to produce a substantial change," he said. "To see the signal of human activity emerge above the noise of natural climate change is in a way a scientific surprise."
Yup, it’s a scientific surprise indeed. Especially since the report he chaired produced this zinger:
The fact that the global mean temperature has increased since the late 19th century and that other trends have been observed does not necessarily mean that an anthropogenic effect on the climate system has been identified. Climate has always varied on all time-scales, so the observed change may be natural.
from IPCC Working Group 1 – The Scientific Basis, section "Observing Anthopogenic Change" found at this link
He even had time to lecture the skeptics:
"They should look at the evidence which has been collected by some of the world’s leading scientists," he said. "I think there are very few scientists who’d disagree with the IPCC. And most of those who do disagree have not published much.
I’ve good news for Sir John. Somebody has looked more closely at the evidence collected by some of the world’s leading scientists. There are now very many scientists who disagree with the IPCC (including some of the IPCC’s own authors). And those who disagree are now publishing like crazy.