From the monthly mean temperature record it is possible to determine the mean temperature for the entire decade. In a word - no. It has been alleged that the Medieval Climate Optimum, when Greenland was actually green and Viking settlers managed to grow crops there, was a localised phenomenon rather than a global warming. However, proxy records from well dispersed regions show similar concurrent warming. There is no evidence of such startling occurrences.
Earth is a moderately large heat sink and takes time to display the effect of various influences.
There's a very easy way to find out. The next graphic represents Earth monthly mean temperatures with a zero mask applied so you can see exactly what we are doing. Note that this offset almost completely masks the positive anomaly. This one anomaly still only makes a difference of one-twentieth of one degree in the mean temperature for the decade but it was apparently sufficient to drive the mean from cooler than average to slightly warmer. It is simply not reasonable to assume that the cumulative effect of five decades of intense industrialisation and fossil fuel use will manifest itself in just one 18 month period.