Satellite temperature datasets are published monthly by the University of Alabama at Huntsville and the Remote Sensing Systems at Santa Rosa, California. They are known simply by the acronyms UAH MSU and RSS MSU and are the publicly available temperature datasets with the highest spatial resolution. Both go back to 1979, now comprising almost thirty years of data.

The data published shows for each month the temperature anomaly - the difference from the temperature measured to the average of a reference period, in this case 1979 - 1998. The following graphs were obtained by averaging the twelve temperature anomalies collected for each year, plus the average of the first semester of 2008.

Global Temperatures

Average Global temperature anomalies for each year since 1979 plus the average of the first 2008 semester with RSS data.

Average Global temperature anomalies for each year since 1979 plus the average of the first 2008 semester with UAH data.

According to the RSS dataset 2008 is being the coldest year since 1993 with an anomaly close to zero (+0.01 ºC). The data from UAH is also presenting 2008 so far as the coldest year since 1993, but with a slightly negative anomaly (-0.03 ºC). According to both datasets there are only eight years on record with average anomalies below 2008: 1979, 1982, 1984, 1985, 1986, 1989, 1992 and 1993. Less than one third of the data is colder than 2008.

Northern Hemisphere

Average Northern Hemisphere temperature anomalies for each year since 1979 plus the average of the first 2008 semester with RSS data.

Average Northern Hemisphere temperature anomalies for each year since 1979 plus the average of the first 2008 semester with UAH data.

Things are not as drastic in the Northern Hemisphere, here 2008 is being the coldest year since 2000 according to RSS and since 1997 according to UAH. On both datasets 2008 is staying in the warmest half of the available years. There are ten years warmer in the Northern Hemisphere than in 2008 according to UAH and thirteen according to RSS. Is is also clear from this graphs the warm seven year period between 2001 and 2007 when the average anomalies stayed above +0.20 ºC, that 2008 is promising to put an end to.

Southern Hemisphere

Average Southern Hemisphere temperature anomalies for each year since 1979 plus the average of the first 2008 semester with RSS data.

Average Southern Hemisphere temperature anomalies for each year since 1979 plus the average of the first 2008 semester with UAH data.

Here can be found the root of the current low temperatures; according to RSS there were only two years colder than 2008 in the Southern Hemisphere, 1984 and 1985. In the UAH dataset 2008 is so far the coldest year on record.

Of note is also the irregular difference between the Northern and Southern anomalies in 2008, by far the highest in the RSS dataset (0.41 ºC) and only surpassed by 1999 in UAH's. This awkward difference should decrease during the following times, to what side remains to be seen, although looking at the raw monthly data the Northern Hemisphere seems to be starting a cooling trend initiated an year earlier in the Southern Hemisphere.

Looking ahead

Will temperatures continue to go down? It remains an open possibility; if the current period of solar inactivity is in fact the major driver behind these recent changes, at least the continuation in time of these negative anomalies should be expected.

The present period of solar inactivity is bound to last, with the minimum twelve months or more away. The smoothed Wolf number is still going down, as so the solar flux. In six months there were just three sunspots belonging to solar cycle 24, the last appearing in April. Before the Sun returns to a visible level of activity, above 10 monthly wolfs, one or two full months without sunspots should be expected.