Here's how to read this diagram: the value plotted at point x = 1980, y = 60 corresponds to the 60-yr trend (°C/yr). (Note: trend is per year, not per decade.) The data source is Hadley's global temperature data (HadCRUT3).
This is from a new paper in BAMS: "Influence of choice of time period on global surface temperature trend estimates," Brant Liebmann et al, Bulletin of the American Meteorological Society, Nov 2010 p 1485. As the authors write:
It is evident that time segments of a few decades or shorter can exhibit either warming or cooling trends, while trends for longer segments are mostly positive, though quite weak compared to those present in shorter segments.
Here's an different presentation of the same data, that shows total temperature change for any interval, versus (as above) the trend: