Friday, 23 December 2011

Precipitation and El Nino

Recently there has been a number of blog postings linking temperature and El Nino. Tamino ( based on a paper by Foster and Rahmstorf used the link to show that global warming had not levelled off. Meanwhile Frank Lansner at WUWT did a similar analysis to show that there had been a levelling off.

One thing which always surprises me is the importance given to temperature by comparison with that given to precipitation. This is very much the case with the previous IPCC report and I am posting it here in the hope that this will change. Within certain wide limits what matters to people is not temperature, and by inference evaporation, but the balance between evaporation and temperature.

The following graph shows a regression plot of precipitation and an El Nino index. The precipitation is based on the NCDC global precipitation anomaly with a 5-month centred moving average. The El Nino index is the NOAA's Oceanic El Nino Index (ONI).

This shows that global precipitation and El Nino are correlated.

The next plots shows the variation in precipiation and the ONI. The precipitation is as above and the ONI is inverted (i.e. the original value multipied by -1).

As can be the two are closely related in both magnitude and timing. The fact that the two are synchronous suggests that neither is forcing the other but that both are a result of a common factor.

In TAR4 very little information was given on the simulation of precipitation by climate models. One of the reasons might have been the fact that the models did not represent the sort of variations shown above.

This should be addressed in TAR5.

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