correction
None of the scientists say that the increase should be constant. They say that while continuing to fluctuate the trend should be up. That means that it is entirely possible for there to be some colder years following warmer ones but that if you take an average over any number of years greater than 4 or 5 it should be warmer than the preceding period. Thats why you get reports like this one:
http://news.nationalgeographic.com/n...mest-year.html
which says that the 9 past years were all in the 25 warmest ever recorded.
This is sort of like the debate about smoking and cancer. It is a statistical argument. You can always find a counterexample (someone who smoked and didnt get cancer or someone who didnt smoke and did get cancer) but overall the evidence shows that there is a correlation. On global warming there are many many fewer data points (i.e. years of weather data) than there are smokers so that the "proof" (such as it is) is correspondingly weaker. However, it is safe to say that the scientists who study this are becoming increasingly convinced and the naysayers are being steadily won over. But there will always be some who dont want to believe it, and they will always be able to point at examples which support their case because that is the nature of statistical evidence. If you are one of these, however, ask yourself this - Why do YOU think the past 9 years are all among the warmest ever recorded? Why do YOU think the Greenland ice cap is melting and chunks of the Antarctic ice the size of Rhode Island are breaking off?
For me, the evidence is pretty clear, but even if it isnt for you most of the things we should do if we believe it (burn less oil, etc.) are all things that would be a good idea for other purely capitalistic reasons (as well as national security ones - wouldnt you love not to NEED oil from the middle east if it were possible?)