Describe the bug
@ESMValGroup/esmvaltool-coreteam do I have time to quickly fix volume statistics for 2.5? The current implementation performs quite poorly and I have been running the function in one year of data with 75 levels for half an hour and it's not done yet. I think that any approach such as da.average(axis=[all axis except time], weights) would be better than the double loop that is implemented right now.

Please attach

• The recipe that you are trying to run, you can find a copy in the run directory in the output directory
• The main_log_debug.txt file, this can also be found in the run directory in the output directory