A statement by Nick is getting repeated and discussed in comments on a previous post discussing RSS. The statement is:

My point was that exceeding the 1998 average is less formidable than exceeding the 1998 peak value of 12-mtm average. 1998 cooled towards the end.

The post on which that comment appears discusses RSS specifically. And when applied to RSS, Nick’s statement happens to be incorrect. (It would be correct for UAH.)

To clarify this, I have updated my graph to show 12 month lagging averages of temperature by adding red circles outlining the averages for months contained in a single calender year. For example, the averages computed based on jan-dec 1998 are circled in orange (click figure to enlarge):

To be specific, I have computed 12 month averages based on the values from RSS available here.

Notice the peak value for the 12 month average for RSS is circled. That’s because the average computed using Jan-Dec 1998 corresponds to the 1998 average temperature. So, when discussing RSS, exceeding the calender year record is no less formidable than exceeding the all time record because they are the same.

As for this statement by Nick:

If 2010 does not cool at the end as 1998 did (big if), then 2010 may still set a RSS record.

This is true. If the Oct., Nov., Dec. temperatures do not decline relative to the September value, the 2010 RSS average will exceed the both maximum all 12 month average RSS temperature and the 1998 calendar year anomaly. In fact, Oct-Dec average need to drop a nearly 0.08C relative to the most recently reported RSS anomaly to avoid breaking the 1998 record. La Nina has arrived and this may well happen– but it also may not.

Still: with regard to the “peak” vs “calendar year” issue: either will break both the calendar year record and the all time high record, or it will break neither. They are both the same record.