The HadCRUT5 data show about a 0.1C increase in annual global temperatures compared to HadCRUT4.6. There are two reasons for this.
- The change in sea surface temperatures moving from HadSST3 to HadSST4
- The interpolation of nearby station data into previously empty grid cells.
Here I look into how large each effect is. Shown below is a comparison of HadCRUt4.6 with HadCRUT5.
Next we estimate the effect of both HadSST4 and interpolation. The previous post showed that my 3D triangulation method agrees almost exactly with HadCRUT5, so I now apply it to HadCRUT4.6. Any differences identifies the HadSST4 component.
Conclusion: There is an increase of recent global temperatures of about 0.1C when moving from HadCRUT4.6 to HadCRUT5. Half of this increase is due to interpolation and half is due to using HadSST4 instead of HadSST3.