NOAA weekly average, March 17-23: 425.37 ppm, up by 4.62 ppm from last year (420.75 ppm)
Scripps weekly average, March 17-23: 425.49 ppm, up by 5.03 ppm from last year (420.46 ppm)
CO2 levels did decrease slightly compared to the previous week, but not enough to drop out of the top-10. The table of largest weekly increases is now dominated by the first three months of 2024.
Scripps data has been unavailable on 3 of the 7 days, and both Scripps and NOAA have shown rather large fluctuations from one day to the next. The data is still good, but this is the time of the year where variability is generally the highest (because CO2 levels now are most strongly dependent on the weather), and it shows.
The ten largest weekly increases on record at NOAA:
#1: 5.75 ppm, 2024-02-04
#2: 5.66 ppm, 2024-03-10
#3: 5.53 ppm, 2024-02-18
#4: 5.07 ppm, 2016-07-31
#5: 4.80 ppm, 2016-06-12
#6: 4.64 ppm, 2024-02-11
#7: 4.62 ppm, 2024-03-17
#8: 4.56 ppm, 2016-04-10
#9: 4.54 ppm, 2016-05-22
#10: 4.45 ppm, 2019-04-28
...
#25: 4.01 ppm, 2024-03-03
OUTLOOK
The end of March also marks the end of the anomalously low CO2 levels we saw in early 2023. At this time last year, we switched from unusually low to unusually high levels. As a result, the time of records should now be over, and I guess we won't see many (if any) more 5+ ppm increases this year. Expect a lot of increases near 3 ppm over the coming two months, but be prepared for the occasional surprise...
In 2023, the week starting March 24th had an average CO2 level of 421.50 ppm at NOAA (420.99 ppm at Scripps). If we stay at the current levels, the weekly average would increase by 3.87 ppm at NOAA (4.50 ppm at Scripps). Levels would have to increase by another 0.6 ppm for a top-10 result (or by 0.15 ppm for a top-25).
The week starting March 31st had an average of 422.64 ppm at NOAA (422.34 ppm at Scripps). Even a weekly average of 427 ppm would no longer be in the top-10 at that point, and we would have to get to 428.4 ppm for a new all-time record. Those are levels that we may not reach this year, not even at the yearly maximum in May.