Accurate Temperature Readings?

Question

On the subject of MMGW (man made global warming) I see temperature graphs going back THOUSANDS and THOUSANDS of years. Since there were no thermometers 100,000 years ago nor technicians to record the temperatures then:

1. How do we know what the temperatures were before the history of weather was tracked?

2a. How accurate are these techniques and is there anyway to verify the accuracy of these techniques? I mean they can say the global temperature was 30.56 degree in 75,235 BCE but without a time machine to go back then....we really don't know....yes?

2b. If the accuracy of these techniques are say +/-2 degrees then is it not dangerous and irresponsible to use this data is making decisions regarding MMGW?

Answer 1

I agree.  Every measuring instrument has an error factor.  But the data presented sometimes are missing that important data.  If we were to make a claim that that rate estimated was greater than anything we had experienced for a period of time, we will also want to know other information like the plus and minus error factor, how the measurement was taken, and how much we can trust the data through time.  

Example:  Estimated average yearly temperatures for Europe 50,000 years ago I would think would be a huge error factor if it is based on deep ice core samples from a spot in Antarctica.  Then you compare it to modern measuring techniques and you would introduce more problems.  

So any data graph should include the data estimated error factor, otherwise the data is almost useless if presented without it.  Just my opinion.

Answer 2

Read up:

http://en.wikipedia.org/wiki/Ice_core