 So let's look at the other factors that might potentially explain some of the variation in this temperature series First of all, we'll look at the Nino 3.4 index. We'll plot that here. That, as we know, is a measure of El Nino variability And you can see that measure on the right axis And so as we can see, there seems to be somewhat of a correlation between Northern Hemisphere land temperatures and El Nino Well, the more obvious examples Is the 9798 El Nino, one of the largest El Nino events on record. That was also associated with an unusually warm year But we see other evidence of relationships between El Ninos and warmer cooler air temperatures So we see the El Nino index, this yellow curve, dips down on this extreme negative value That was an unusually cold year in 1917 So we might expect there's a positive relationship between these two times, two time series That we can explain some of the variation in Northern Hemisphere temperature series with El Nino Now let's finally look at the NaO index. Let's plot that here, year and NaO Make that a line plot. That's here in green. Let's turn this one off Again, we can see somewhat of a positive relationship Usually in warm years and in some cases appear to be associated with a positive NaO index So we might expect that El Nino and the NaO can explain some of the remaining variation in our energy Our energy balance model simulation didn't explain and so our next step would be to try all three factors at once