Drew Shindell is a physicist and an ozone specialist and professor at Duke University's Nicholas School. His H-index is 79 and he is listed as an ISI Highly Cited Researcher... (wikipedia)
So in seven years, we've caught up with El Nino-like conditions.
It's fair to say that it probably is the warmest since we have modern meteorological records.
It's basically all of the temperatures at the surface that we can get our hands on.
Instead of being this tiny player, (ozone) can be more like 30 or 40 or even 50 percent of the cause of warming that we're seeing in the Arctic now. It's very dramatic.