The question of how do we measure global warming is actually quite simple. Located in Hawaii is a measuring station as it is in the middle of the Pacific allowing for the best location of air passing from the continents.
First of all you should know that CO2 is the greenhouse gas that we are most worried about in global warming but it actually only takes up around .039% of of which is such a small number it makes measuring quite difficult. Chemist and other sciences use something called "parts per million" to measure such small amounts. Just to give you and idea, environmentalist and most scientist agree that 350ppm (part per million) of CO2 in the atmosphere is the safe amount to have. The fact that we have passed 350ppm is that reason for so many extinctions and the climate change we are seeing.
If you were to put one drop of water in a 50 litre gas tank (size of a compact car) that would be equivalent to 1ppm (part per million). Or you could also say that 30 seconds out of an entire year is 1 ppm (part per million). This is very important that average people understand this because if it sounds just like scientist talk then it will feel like something you can do nothing about. As you can see it is actually pretty easy to understand the measuring system.
So this leaves us at the ability the non-scientist population to be able to see the CO2 ppm everyday with the chart I posting above. Remember 350ppm is the recommended safe mark for humans. Take a look at where we are now and you might think that it is safe to be there because you everyday life is going on as is but it is time to realize that we are losing somewhere between 20,000 and 50,000 species a year as compared to 4 species a year before 1800. Nothing to panic about just a way for you to see that it's now time to change the way we live.