Quote:
Our results show that the average temperature of the earth’s land has risen by two and a half degrees Fahrenheit over the past 250 years, including an increase of one and a half degrees over the most recent 50 years.


Let's see...

In the first 200 years the temp went up 0.5 degrees or 0.5/200 = 0.002 degrees/year. Then in the next 50 years (the last 50 years) it went up 1.5 degrees or 1.5/50 = 0.03 degrees/year. So in the last 50 years this would be 0.03/0.002 = 15 times the rate of increase as in the first 200 years.

It is obvious that man was emitting little greenhouse gases in that first 200 years and emitting a lot of greenhouse gases in the last 50 years. So, there IS a correlation between temperature increase and the amount of greenhouse gasses being emitted.

This would seem to indicate that greenhouse gases have vastly increased the rate of temperature increase. Of course, there is also a possibility that there is some other unknown factor that is causing the temperature increase. But in absence of any evidence of that factor, our best conclusion is that the cause is greenhouse gases.