IF you had paid more attention in "science class" you might have learned that no measurement is ever exact. Nor is an exact measure needed.
I thought I explained this before, and I certainly have in other threads: we appear to be in a long term cooling trend. The effects that cause global warming are increasing much more rapidly and are of greater magnitude than the ones that have been producing cooling over recent time periods.
I don't know who taught you in "science class" and I don't know if it was a high school class or a lower level college course of some sort. But the title you give it does not inspire confidence in the accuracy of information transfer. That is why university science classes are taught by actual scientists. They are supposed to get the facts right, and explain how cogent theories are tested and "proved" or disproved.
It is of no relevance whether you "buy it" or not. We don't do science by consensus. If you are too lazy to educate yourself, then are doomed to live in ignorance.
On the odd chance that you are educable, here is a little something to get you started:
http://www.sciencemag.org/cgi/content/abstract/321/5889/680
I think I am going to start putting the worst meat heads on Ignore. You might be first since some of the most egregious seem to have gone back on their meds recently.