Thanks for your comment, but I am not sure what part of the analysis or discussion is not clear. Are you saying that the three consecutive years of La Nina has never happened before? Three-year La Ninas are rare but not unprecedented (see, 1974-1976 and 1999-2001). Regardless of how rare they are, the main point is that La Nina does not affect long-term global warming caused by increasing greenhouse gases - it merely tends to cause a temporary downward fluctuation in globally averaged temperature. 

However, if you are wondering if the recent three-year La Nina may have some relation to the long-term ocean trends that could have a relationship with increasing greenhouse gases, then this post discusses the debate on this important topic.