 Okay, 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 take a look at the NINU 3.4 index that, as we know, is a measure of El Nino variability. I'll choose axis B here as an option to put these on roughly the same scale. And so, as we can see, there is a positive correlation between El Nino and Northern Hemisphere average temperatures. One of the more obvious examples is the 1997-98 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 leading to warmer land air temperatures in a given year. And the opposite, La Nina leading to relatively cold temperatures. So when we see the El Nino index, this red curve dips down to this extreme negative value. That was an unusually cold year, somewhere around 1920 or so. So we might expect that there's a positive relationship between these two series, in that we can explain some of the variation in the Northern Hemisphere temperature series with El Nino. Let's look finally now at the NAO index. And again, we can see a positive relationship. Unusually warm years in some cases appear to be associated with the positive phase of the NAO index. So we might expect that El Nino and the NAO can explain some of the remaining variation that our energy balance model simulation didn't explain. And our next step will be to try all three factors at once.