Since NOAA has announced that their data show July 2009 global-average sea surface temperatures (SSTs) reaching a record high for the month of July, I thought I would take a look at what the combined AMSR-E & TMI instruments on NASA's Aqua and TRMM satellites (respectively) had to say. I thought it might at least provide an independent sanity check since NOAA does not include these satellite data in their operational product.

The SSTs from AMSR-E are geographically the most complete record of global SSTs available since the instrument is a microwave radiometer and can measure the surface through most cloud conditions. AMSR-E (launched on Aqua in May 2002) provides truly global coverage, while the TMI (which was launched on TRMM in late 1997) does not, so the combined SST product produced by Frank Wentz's Remote Sensing Systems provides complete global coverage only since the launch of Aqua (mid-2002). Through a cooperative project between RSS, NASA, and UAH, The digital data are available from the same (NASA Discover) website that our daily tropospheric temperatures are displayed, but for the SSTs you have to read the daily binary files and compute the anomalies yourself. I use FORTRAN for this, since it's the only programming language I know.

As can be seen in the following plot of running 11 day average anomalies, July 2009 was indeed the warmest month during the relatively short Aqua satellite period of record, with the peak anomaly occurring about July 18.
Global SST
© Dr. Roy Spencer

The large and frequent swings in global average temperature are real, and result from changes in the rate at which water evaporates from the ocean surface. These variations are primarily driven by tropical Intraseasonal Oscillations, which change tropical-average surface winds by about 2 knots from lowest wind conditions to highest wind conditions.

As can be seen, the SSTs started to fall fast during the last week of July. If you are wondering what I think they will do in the coming months, well, that's easy...I have no clue.