Graph showing daily averaged atmospheric carbon dioxide (CO2) levels from four observatories since 2010. The observatories are in Barrow, Alaska, USA (blue), Mauna Loa, Hawaii, USA (red), American Samoa (green) and Antarctica (yellow). The levels are given in parts per billion. Levels of carbon dioxide have risen due to the combustion of fossil fuels and deforestation. The thick black lines represent the average of the smoothed seasonal curves and the smoothed, deseasonalised curves for each of the records.