2021 will be the coolest year since 2018, ending up between 0.7C and 0.8C warmer than the baseline climate of 1961 to 1990. This spread mainly depends on which SST dataset you use.
There are two versions of HadSST namely version 3 and version 4. My calculations of temperature to date were always based on Version 3. Version 4 gives higher 21st century temperature anomalies than Version 3 but is said to be more accurately aligned to floating buoys. Neither dataset had been updated since September until 2 days ago. Version 3 was updated just for October while HadSST4 was updated for October and November. Consequently I calculated two sets of results using my spherical triangulation method. The monthly comparisons are shown below.
The overall effect is a systematic increase in recent global temperatures by ~ 0.05C . The H4 global temperature for October is 0.97C and the H3 temperature is 0.92. The November temperature is only available for H4 and is 0.88C.
The annual temperatures for 2021 (11 months for H4 and 10 months H3) are shown below.
Using H3 results in 2021 being the 6th equal warmest year, while using H4 2021 becomes the 4th warmest year.
Here is a spatial comparison between the two results
Here is an animation for November 2021 V4S4 (HadSST4)
Australia looks much cooler than normal!
I will probably use HadSST4 in future as it seems to be better accepted and supported. Here are the arguments as to why many climate scientists believe it is better.