Baseline Impact

 Temperatures are rising non-uniformly globally.  This compares the extra tropics and tropics using the GISS LOTI data  from 1941 to 2011 using the full average as a baseline.  Using a simple linear regression and extending the X-axis to the year 2080, both the tropics and southern extend would be expect to warm to ~0.75 degrees above the baseline.  The Northern extent would be expect to warm more to ~ 1.25 degrees above the baseline.

 Using the same data with a 1980 to 2011 average for a baseline the linear regression indicates about the same warming would be expected in the tropics and Southern extra-tropics with more more warming expected in the Northern extra-tropics, ~2.8 degrees of warming instead of 1.75 degrees.

Using the full data series with the1880 to 2011 average as a baseline, then southern extra-tropics amy be expected to warm by about the same 0.75 degrees, the tropics less to ~0.55 degrees and the northern extra-tropics to ~1.1 degrees.

There is obviously a larger oscillation in the northern extra-tropics with a physical explanation, the Northern extra-tropics have more land and less ocean than the rest of the world, so they have lower heat capacity or thermal mass.  The northern extra-tropics would be more sensitive to change than the rest of the world.

So will the region of the Earth with the least thermal mass drive the rest of the world to a much warmer temperature or will the more stable southern extra-tropics dampen the impact of the larger swings in temperature in the Northern extra-tropics?  Which choice of baseline would be a better indication of the expected change?