Some climatologists have criticized the attention that the popular press gives to "warmest year" statistics; for example, Gavin Schmidt stated "the long-term trends or the expected sequence of records are far more important than whether any single year is a record or not." Of the 20 records, Schmidt stated that the 2014–16 El Niño event was "a factor ...
but both 20 would have been records even without it"; he attributed about 90% of the warming in 2016 to anthropogenic climate change.
Volcanoes are the largest source but there are also anthropogenic sources. Some aerosols like carbon black have warming effects.
Land use change like deforestation can increase greenhouse gases through burning biomass. Incoming solar radiation varies very slightly with the main variation being an approximately 11-year cycle.
Global mean surface temperature change from 1880 to 2017, relative to the 1951–1980 mean.
Global surface temperature change for the period 1980–2004.
Land air temperatures are rising faster than sea surface temperatures.
Over 1979 to 2012 the trend for land was about 0.254 ± 0.050 °C per decade per Cru Temp4 or 0.273 ± 0.047 per GHCN while the trend for sea surface temperatures is about 0.072 ± 0.024 °C per decade per Had ISST to 0.124 ± 0.030 °C per decade per Had SST3 The IPCC Fourth Assessment Report found that the instrumental temperature record for the past century included urban heat island effects but that these were primarily local, having a negligible influence on global temperature trends (less than 0.006 °C per decade over land and zero over the oceans).
The blue line is the monthly average, the black line is the annual average and the red line is the 5-year running average.
Data source: Greenhouse gases trap outgoing radiation warming the atmosphere which in turn warms the land.