The decrease is seen in the land only data. Data from the sea shows a decline but not as much. This is expected given the ocean’s thermal lag. Data from the RSS group that provides satellite temperature services show that late-2016 temperatures have returned to the level it was at post-1998, Fig 1. Click on the image to enlarge.
This clearly shows the recent El Nino for what it is – a short term weather event. Now that it is over it can easily be seen that the lower Tropospheric temperature displays no long-tern trend between 1999 – 2016. The same is seen in the UAH analysis of the satellite data. Fig 2.
Many have noticed that the strong El Nino of 1998 resulted in a “step-change” in lower atmospheric temperature. There is no reliable statistical evidence for an increase before it in the satellite data that was available in 1979. After 1998 the temperature did not return to its previous level but remained at a higher, stable level. It remains to be seen if the temperature will undergo another step-change. It’s very early days but on the sparse data available I think it seems unlikely.