Is it important that climate scientists are "careful scientists"?

We know that the global warming or climate change issue is a very big one. In fact, many have claimed it's the single most important issue in the history of mankind with perhaps civilization as we know it being threatened. I'd like to ask about the very important claim that recent warming is unusual or... show more We know that the global warming or climate change issue is a very big one. In fact, many have claimed it's the single most important issue in the history of mankind with perhaps civilization as we know it being threatened. I'd like to ask about the very important claim that recent warming is unusual or unprecedented.

In Climategate email "0983566497.txt" Chick Keller says to Mann, Jones, Briffa, et al:

"Anyone looking at the records gets the impression that the temperature amplitude for many individual records/sites over the past 1000 years or so is often larger than 1°C. They thus recognize that natural variability is unlikely to generate such large changes unless the sun is having more effect than direct forcing, or there is some fortuitous but detectable combination of forcings. And they see this as evidence that the 0.8°C or so temperature rise in the 20th century is not all
that special."

"I note that most proxy temperature records claim timing errors of +-50 years or so. What is the possibility that records are cancelling each other out on variations in the hundred year frame due simply to timing errors?"

"...many careful scientists will decide the issue is still unsettled and that indeed climate in the past may well have varied as much or more than in the last hundred years."

The above email is discussing past temperature reconstructions like Mann's "hockey stick" which essentially averaged out variability and produced the relatively flat "handle" of the hockey stick from 1000AD-1900AD. This of course led to the conclusion that the warming from 1900AD was not only unusual but unprecedented.

On a NASA website, they go even further by comparing the past century warming to the rate of warming coming out of the past ice age: "As the Earth moved out of ice ages over the past million years, the global temperature rose a total of 4 to 7 degrees Celsius over about 5,000 years. In the past century alone, the temperature has climbed 0.7 degrees Celsius, roughly ten times faster than the average rate of ice-age-recovery warming."

Given the discussion in the above email, how can that NASA statement be justified b comparing a 5000 year period to a 100 year period?

And if you think this issue is simply an old one (that Climategate email is from 2001), there was a study just announced yesterday. Google: Warming since 1950 ‘unprecedented' The story is about a study just announced yesterday. Scientists studied 1000 years of temperature records for Australia and concluded that it suggests "...a strong influence of human-caused climate change in the Australasian region," based on not finding any natural variability to suggest otherwise.

This is odd because if you go to a website like skepticalscience.com, you can read statements like this: "While Greenland showed strong warmth 1000 years ago, global temperature during the Medieval Warm Period was less than today." So one group of scientists point to Australia and claim support of AGW and another point to Greenland and claim the contradictory evidence doesn't matter.

I've just focused on one very narrow issue but it is an extremely important one. If recent warming is not unusual, then the worry about AGW would drop dramatically.

So I'll go back to my original question: Is it important that climate scientists are "careful scientists"? What evidence can you present that they are or are not?
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