For example. Girma shows HadCrut3 from 1850 to 2011 inclusive.
I calculate the trend to be 0.45 C/century. I don’t think Girma is doing any calculations at all. His 0.6 per century is way off what his graph shows.
You cannot arbitrarily pick the beginning and end years in a trend calculation of data that shows oscillation. The start and end years must be at the same stage of the oscillation cycle. We know that the 1880s where global mean temperature peaks. We also know that the 2000s were global mean temperature peaks. As a result, these two years may be used as start and end points in calculating the global warming trend :
Graph => http://bit.ly/xxMj6K
Data (0.06 deg C per decade warming) => http://bit.ly/wav7fq