It might not take that long again, but there'd have to be 6 month full time period. (slaw.ca)
Putting $ 1,000 per month into an account that earned an interest rate equal to a three - month Treasury Bill starting in 1980 would have given a reluctant cash investor about $ 789,000 over the full time period. (regentatlantic.com)
Figure 2: The data (green) are the average of the NASA GISS, NOAA NCDC, and HadCRUT4 monthly global surface temperature anomaly datasets from January 1970 through November 2012, with linear trends for the short time periods Jan 1970 to Oct 1977, Apr 1977 to Dec 1986, Sep 1987 to Nov 1996, Jun 1997 to Dec 2002, and Nov 2002 to Nov 2012 (blue), and also showing the far more reliable linear trend for the full time period (red). (skepticalscience.com)