I feel that the El Nino/Nina cycle provides a great tool for seeing into the future (next decade) as the short term temperature spikes give us a taste of what will happen as the temperature trend hits those spike levels.
The soil/forest carbon turnaround during the last El Nino is extremely worrying, as it seems to show that somewhere between 1.5 degrees and 2 degrees we will get big moves from carbon sinks to carbon sources - negating any anthropogenic reductions (I silently laughed as I wrote those last 2 words given the recent jump in Chinese emissions).
Some of these feedbacks can become self-driving, even if temperatures fall back. The loss of forest leads to reduced rainfall, the microbes that digest the organic material in permafrost are exothermic etc. So a big unknown is whether an El Nino event could kick off feedbacks that continue during the Nina part of the cycle.
I also see the feedbacks as being highly connected, with one of them kicking temperatures to the point where another feedback kicks in. The finding that climate sensitivity increases with temperatures lends some support to this view.
