It's true that some scientists have made very dour (and wrong) predictions about, for example, over population.

But no-one argues the fact that the average global temp has increased dramatically, compared to the previous thousands of years, in the last 100 years. That's lightening fast on a geologic scale, but still pretty slow on a human scale.

My point is: don't throw the baby out with the bathwater. Just because some people overstated the case doesn't mean it's all bunk.