Warning covers the next 24 h. It is based on the highest awareness level during the warning period.
Northern hemipshire temperature-anomalies from 4 different sources what at available on the net.
Noteble here are that every source use different timeframe as "normal" average and also that for how long time backvards data are available vary. Data are updated once a month.
Measured with NOAA-satellites.
Data from year: 1979
Data courtnesy of University of Alabama/National Space Science and Technology Center (NSSTC) .
Surface data: Global Historical Climate Network (GHCN)
Ocean data: Extended reconstructed sea surface temperature (ERSST)
Data from year: 1880
Data courtnesy of NOAA/National Climatic Data Center (NCDC) .
Data courtnesy of UK MetOffice/Hadley Centre .
Disclaimer: This is not a declaration for or against global warming, just shows the differences between different data sources.