Hi Rog, Roger,
Here is a bit more information on the topic of S. Hemisphere temps. I understand that you know much of this, but I thought that some might find the background helpful. I don't mean for it to sound pedantic.
Below is a link to three graphs from the Hadley Center in East Anglia, England. Part of the Met Office, The Met Office Hadley Center “provides a focus in the UK for the scientific issues associated with climate change.” These graphs are from the Hadley web pages.
The graphs chart global temperature data from 1850 to the present,and show temperatures of the Northern and Southern Hemisphere, (land plus ocean surface), as well as global, land plus ocean surface.
In all three graphs, the last century’s upward trend is obvious. Also obvious is the difference between the N. Hemisphere/S. Hemisphere trends. The ocean is much slower to show a temperature increase because it absorbs and dissipates incoming energy. Land surfaces warm at a faster rate, and the difference in the NH/SH trends is due largely to the greater amount of ocean in the SH. With its larger percentage of land, the NH warms faster.
In this larger graph, without error bars, it is also apparent, especially in the SH and the combined global graphs, that recent annual temperatures are cooler. This downturn, however, does not mean that the climatic warming trend has stopped. Only time will tell if the recent Hadley data turns out to be a cooling trend, but the recent ten-year period is the warmest (globally) decade in the 167 year Hadley record.
As Rog pointed out, the influence of an El Nino or La Nina can have a large impact on short-term global temperatures. As seen in this graph from NASA, the relatively strong 1997-98 El Nino had a large influence on the 1998 spike in global temperatures. But the influence was short term. In the same way, the graph shows that the current mature La Nina is having a pronounced downward effect on global temperatures. A representative from Hadley estimates the downward temperature effect of the current La Nina as high as 1.5C. (The wording of that estimate could be clearer, however, and the 1.5 C number may be in error.) But, at any rate, La Ninos and El Ninas transport a large amount of energy between the climates sub systems.
The sun is also currently near the minimum of the 10-11 year solar cycle. The effect of this solar cycle on earth temperature is estimated to be about .1 C over the range of the cycle, but the energy does not accumulate. The small signal, in either the rising or falling phase,is difficult to disentangle from other causes of global temperature changes, but the sun is currently near the bottom of the cycle.
Another temperature record is available from the Goddard Institute at NASA. GISS (Click on the top right "Graphs" and scroll) does not graph combined land and ocean temperatures for the individual hemispheres, but GISS does separate land-based temperatures by hemisphere. Again, because land temperatures warm and cool faster than ocean, the “land temperature only” charts will show a stronger trend than the Hadley graph above that showed land plus ocean temperatures. The Hadley and GISS data for land based Southern and Northern Hemisphere temperatures can be compared. In the Hadley data the last number on the right is the annual anomaly. The annual anomaly in the GISS data is identified.
Hadley NH land based temperatures
GISS NH land based temperatures
Hadley SH land based temperatures
GISS SH land based temperatures
There are small differences in the Hadley and GISS temperature record output, and there are small differences in the data collected, and how the data is interpreted. The treatment of the Arctic is one of the larger differences. The Hadley record does not include much of the Arctic latitudes, but GISS interpolates areas of the Arctic waters from adjacent temperature stations. Since the Arctic latitudes warm more than mid and tropical, and have recently experienced pronounced temperature increases, the different methods of data treatment would be expected to influence results in the Hadley and GISS records, and they do.
Another difference in the Hadley/GISS series is the period on which the records are based. GISS temperature anomalies (temperature measurements above or below the base period norm) are calculated against the years 1951 to 1981. Hadley calculates its anomalies based on temperatures between 1961 and 1990. Since 1961-1990 was a warmer period, the Hadley anomalies are lower numerically. A comparison of the two records requires a conversion to a common base. When this is done the records are remarkably similar, although Hadley numbers are slightly and consistently lower. Nevertheless, and perhaps more importantly, with a few exceptions, the two records move in nearly parallel fashion.
Unlike the references above which link directly to Hadley and GISS, the following graph is taken from the website Open Mind. The host, or moderator of this site, Tamino, is a mathmatician who often posts on climate issues. Tamino recently converted GISS, HadCRU, (Hadley), and the NCDC (National Climate Data Center) temperature records to a common base and charted the curves. The generally cooler HadCRU temperatures are apparent, as well as HadCRU’s relatively high anomaly for 1998. HadCRU’s 2005 and 2007 anomaly is also lower than GISS or NCDC. Consequently, the HadCRU record, is often the record used as evidence that global warming "stopped" in 1998. With a lower 1998 anomaly and higher anomalies in 2005 and 2007 the GISS record is not as compatible with this argument. Through calculations of regression-line fit and residual computations, Tamino concludes that none of the three temperature records provide statistical evidence that the recent warming trend, that began in 1975, has stopped. Only more time and data will tell. The brief analysis is an interesting read.
This page also includes sea surface temperatures and some documentation and explanation of Hadley’s temperature data and its treatment.
Finally, climate data are best sampled over at least twenty-thirty years, and even this time period seems paltry when considering earth’s climate history. If the warming trend since 1975 continues statistically, the GISS graph above, charting the static annual global temperatures over the last decade is worth a second look. The graph clearly shows the annual variability in global temperature, and the potential of El Nino or La Nina to drive short-term internal variation. But this variability is statistical noise, or weather, rather than climate. And like this graph of static but high annual temperatures, the Hadley data also point to a very warm first eight years of the twenty-first century. For example, using the three data sets, HadSST, (Sea surface), HadCRUT3, (Land and sea combined) and CRUTEM3, (Land only) for the Southern Hemisphere; a comparison of the sum of the eight annual temperature anomalies 2000 through 2007, with the sum of the ten temperature anomalies 1990 through 1999, reveals that the eight anomalies from this uncompleted decade, add to a higher positive sum than the ten anomalies from the full decade of the nineties; in all three data sets. Through eight years of this decade, SH oceans, SH land, and SH land and ocean combined, are, in sum, warmer than the full decade of the nineties. The same is true for global temperatures, but I didn’t check the N. Hemisphere.
I apologize for the long post. I tried to keep it narrow.