Description: This visualization contains the solution of week 2 assignment of ‘Data Visualization’ course from Coursera.
Below is a summary of the original data.

##       Year           Glob             NHem              SHem          
##  Min.   :1880   Min.   :-47.00   Min.   :-52.000   Min.   :-47.00000  
##  1st Qu.:1914   1st Qu.:-20.00   1st Qu.:-21.500   1st Qu.:-22.50000  
##  Median :1947   Median : -8.00   Median : -2.000   Median : -9.00000  
##  Mean   :1947   Mean   :  1.63   Mean   :  3.326   Mean   : -0.07407  
##  3rd Qu.:1980   3rd Qu.: 17.50   3rd Qu.: 16.000   3rd Qu.: 25.00000  
##  Max.   :2014   Max.   : 75.00   Max.   : 91.000   Max.   : 59.00000  
##     X24N.90N          X24S.24N          X90S.24S          X64N.90N       
##  Min.   :-61.000   Min.   :-61.000   Min.   :-48.000   Min.   :-158.000  
##  1st Qu.:-26.000   1st Qu.:-22.000   1st Qu.:-26.000   1st Qu.: -47.500  
##  Median :  2.000   Median : -3.000   Median :-11.000   Median :   3.000  
##  Mean   :  5.415   Mean   :  1.926   Mean   : -2.704   Mean   :   9.022  
##  3rd Qu.: 21.000   3rd Qu.: 23.000   3rd Qu.: 21.000   3rd Qu.:  58.000  
##  Max.   :110.000   Max.   : 72.000   Max.   : 58.000   Max.   : 211.000  
##     X44N.64N          X24N.44N           EQU.24N         
##  Min.   :-70.000   Min.   :-57.0000   Min.   :-70.00000  
##  1st Qu.:-27.000   1st Qu.:-19.5000   1st Qu.:-23.50000  
##  Median :  0.000   Median : -8.0000   Median : -3.00000  
##  Mean   :  9.163   Mean   :  0.7111   Mean   :  0.08148  
##  3rd Qu.: 34.500   3rd Qu.: 13.5000   3rd Qu.: 19.50000  
##  Max.   :129.000   Max.   : 77.0000   Max.   : 72.00000  
##     X24S.EQU          X44S.24S           X64S.44S          X90S.64S       
##  Min.   :-55.000   Min.   :-43.0000   Min.   :-62.000   Min.   :-237.000  
##  1st Qu.:-22.000   1st Qu.:-23.0000   1st Qu.:-27.500   1st Qu.: -41.000  
##  Median : -3.000   Median : -9.0000   Median : -9.000   Median :   5.000  
##  Mean   :  3.748   Mean   :  0.7926   Mean   : -7.593   Mean   :  -5.119  
##  3rd Qu.: 29.500   3rd Qu.: 22.0000   3rd Qu.: 16.000   3rd Qu.:  37.500  
##  Max.   : 81.000   Max.   : 76.0000   Max.   : 38.000   Max.   : 136.000

Global

The following graph represents the change in average global temperature as it varies form 1880 to 2014 as recorded. An continuously incerasing trend after 1970s is clearly visible from the plot below. The thin curve shows the actual variation and the thick curve shows the smooth curve generated from the same data.

ggplot(data=data2,aes(x=Year,y=Glob))+geom_line(colour="blue",size=0.5)+geom_smooth(colour="blue",size=1.25)+labs(x="Year",y="Temp(F)")+ggtitle("Global Average Temperature")

North vs South Hemisphere

Both northern and southern hemispheres have shown increasing trend of temperature, the northern being hotter for few decades now. The slope of increase for average temperature for northern hemisphere appears higher than the southern hemisphere indicating the effect of global warming in the same region.
The north hemisphere has more land in tropical and sub-tropical region where the temperature is generally high and these observations generate as an average of all these observations. So, it could be faulty to judge the graph on the basis of magnitute only.

ggplot(temp,aes(x=Year,y=value,colour=variable))+geom_line(size=1)+scale_color_manual(values = c("magenta","blue"))+labs(x="Year",y="Temp(F)")+ggtitle("North vs South")

Note

The x-axis here shows years from 1880 to 2014 on a linear scale and the y-axis shows temperature in Fahrenheit.
A subset of the original data was used and was done so by melt method from reshape2 and filter method from “dplyr”. This was important as all of the data was not necessary for visualization as it could have reduced the claroty and readibility of the plot.
The rest two questions have been answered in the plot description above.