Genuine science is always based on reality, never dogma. And there are two issues regarding reality:

1. Nature gives consistent answers based on empirical analysis.  So those answers will tend to be reliable.
2. Human beings are fallible. That means they make mistakes and do not always make precise measurements.

A contradiction? Not really. Look at these two charts:

http://www.cmar.csiro.au/sealevel/sl_hist_few_hundred.html

http://en.wikipedia.org/wiki/File:Hockey_stick_chart_ipcc_large.jpg

The light blue areas in the first graph, and the grey areas in the second, are uncertainties resulting from the fact that there were fewer measurments relative to earlier time periods than later ones. There were far fewer tide gauges in the late 19th Century than in the late 20th Century. And there were far fewer proxies extending back to the Middle Ages than those which referred only to modern times. And in both charts, there are more precise measurements of sea level (from satellites) or of temperatures (from direct thermometer readings).

Scientists take pride in their honesty, so they allow for errors and uncertainty in their data, even while attempting to increase the accuracy and detail of their measurements. Even if the actual sea levels or temperatures centuries ago were not exactly known, we can still give approximate estimates that are better than knowing nothing at all.

Contrast these two charts with this one:

http://www.publications.parliament.uk/pa/ld200506/ldselect/ldeconaf/12/12we18.htm

Where is the uncertainty? This chart seems to depict EXACT measurements of sea levels from hundreds of years ago, which is really impossible! But those who are scientifically illiterate (like many members of the British House of Lords, I would guess), would not realize that!

Which explains why I commented on this chart and others here:

How the hell is it that denialists are willing to accuse the makers of the “hockey stick” graphs of faking data, yet they never noticed anything from their own people like THAT?!

Ironically, when you have no uncertainty allowed for in the data, THAT is a sign of fakery!

Related Articles

• Global Average Temperature: What It Isn’t (wmbriggs.com)
• How to Live with Uncertainty (psychologytoday.com)
• Dogma versus science (scienceblogs.com)
• The Use Of Uncertainty (randi.org)