set term pngcairo font 'Sans,14' size 1024,768

# Parse the time series output from JGC's perl script
# and setup the x axis so there's a tic every 20 years
set xdata time
set timefmt "%Y.%m"
set format x "%Y"
set xrange ['1840.01':'2020.01']
set mxtics 0
set xtics "1840.01",631100000,"2020.01"

# Use pm3d to map the values to a colour.
# We use a narrow cbrange around white, to give more vivid colours
set view map
set pm3d explicit
set cbrange [-3:3]
set palette defined (-3 "#0000FF", 0 "#FFF0F0", 3 "#FF0000")
unset colorbox

set xzeroaxis
set ylabel "°C difference from 1961-1990 average"

set title "Global temperature trend"
set output "global.png"
# The last :2 specifies that the palette colour is determined by the y value
splot "MetOffice08122009TrendGlobal.dat" using 1:2:2 notitle with lines palette

set title "Northern hemisphere temperature trend"
set output "north.png"
splot "MetOffice08122009TrendNorth.dat" using 1:2:2 notitle with lines palette

set title "Southern hemisphere temperature trend"
set output "south.png"
splot "MetOffice08122009TrendSouth.dat" using 1:2:2 notitle with lines palette