A 2016 study analyzed temperature records over land for the Northern hemisphere since 1951 expressed as a standardized value relative to the local average of the reference 1951 1980 period temperature anomalies meaning that a value of 1 represents 1 standard deviation above the local mean for the reference period The data are shown below for summer top and winter bottom temperature records The dotted green line is a Normal curve modeling the 1951 80 reference period shown in each following decade for easy comparison Blue indicates seasonally cool temperatures red indicates seasonally warm temperatures 1951 1980 33 5 33 1 1951 1980 Shifting Distribution of Temperature Anomalies Northern Hemisphere Land June July August 1983 1993 1994 2004 Select 23 0 32 8 34 5 47 7 22 3 10 3 2 7 14 5 0 1 6 5 4 3 2 1 0 1 2 3 4 5 6 5 4 3 2 1 0 1 2 3 4 5 6 5 4 3 2 1 0 1 2 3 4 5 6 5 4 3 2 1 0 1 2 3 4 5 6 Shifting Distribution of Temperature Anomalies Northern Hemisphere Land December January February 1983 1993 2005 2015 48 9 1994 2004 61 4 11 5 8 0 61 6 2005 2015 5 8 67 0 14 6 A similar pattern is noticed for winter temperature anomalies although it is Select 2 6 4 1 0 0 0 5 6 54 3 2 1 0 1 2 3 4 5 6 5 4 3 2 1 0 1 2 3 4 5 6 5 4 3 2 1 0 1 2 3 4 5 6 5 4 3 2 1 0 1 2 3 4 5 6 Fig 6 Frequency of occurrence vertical axis of local seasonal mean temperature anomalies in unit of local standard deviation of Northern Hemisphere land areas Upper row is for summer and lower row for winter A Normal distribution is Select 58 2 model for the distribution of local seasonal temperature anomalies in a given time period Over time the distribution of summer temperature anomalies in Northern Hemisphere land areas shows Select standard deviation compared with the 1951 1980 reference period as in the summer mean and