A major unanswered question with respect to climate change remains, what is the actual global surface air temperature? It is regularly reported "if it reaches 1.5°C, it will be the tipping point of the climate". I have tried to find out, visiting NOAA, NASA, WMO, ECMWF ECMWF, and the UK Met Office website with no luck.
I cannot find the answer to a very simple question from the main weather/climate institutions. There are plenty of references to temperature differences in respect to a set periods of time (a 30-year climate!), called anomalies.
From the UK Met Office "Absolute temperatures are not used directly to calculate the global-average temperature. They are first converted into 'anomalies', which are the difference in temperature from the 'normal' level. The normal level is calculated for each observation location by taking the long-term average for that area over a base period. For HadCRUT4, this is 1961-1990."
This is what NASA have to say "The term temperature anomaly means a departure from a reference value or long-term average. A positive anomaly indicates that the observed temperature was warmer than the reference value, while a negative anomaly indicates that the observed temperature was cooler than the reference value.
What can the mean global temperature anomaly be used for? This product is a global-scale climate diagnostic tool and provides a big picture overview of average global temperatures compared to a reference value."