Much has been written this year about the 2015/2016 El Nino and about the apparent record global temperature anomalies. Professor Michael Mann of Penn State University was quick to provide his opinion that the El Nino contributed only about 0.1oC, or about 15%, to the 2015/2016 global average temperature anomaly increase. Others provided estimates ranging from 0.07oC to 0.2oC. The balance of the temperature anomaly increases was attributed to the continuing increase in atmospheric CO2 concentrations as the result of human fossil fuel combustion.
However, the 2015/2016 El Nino is now over; and, global temperature anomalies have dropped sharply: by approximately 0.4oC overall; and, by approximately 1.0oC over land only. The sea surface temperature anomalies are expected to decrease further, although more slowly, especially if a significant La Nina develops in 2017. The equatorial Pacific is in a weak La Nina condition at present, but La Nina conditions appear to be weakening.
Regardless, Mann and others who minimized the potential contribution of the 2015/2016 El Nino to the rapid global temperature anomaly increases in those years are now faced with explaining the large, rapid decreases in the global average anomalies following the end of the El Nino. It would be difficult enough to explain rapid anomaly increases in association with slow increases an atmospheric CO2 concentrations; but, even more difficult to explain rapid anomaly decreases in association with slow increases in atmospheric CO2 concentrations.