The map – a thermally enhanced satellite photo – below shows September 2015 sea surface temperature anomalies – that is the difference from average temperatures over a period. During the most resent El Niño. The oceans have a sun warmed surface layer overlaying the cold depths. Wind and planetary spin keep oceans and atmosphere constantly in motion. In places surface water sinks – driving deep ocean currents – and in others it upwells. Energy moves from the Sun to oceans and land from tropics to poles, to the atmosphere and out to space. It is technically a coupled, nonlinear system far from thermodynamic equilibrium. A characteristic behavior of the Grand Climate System is relatively stable states punctuated by abrupt shifts that owe more to internal dynamics of the system as a whole than external factors such as greenhouse gases. Traditionally called oscillations. They are shifts in patterns of ocean circulation triggered by small changes in the Earth system. Such as orbits and greenhouse gases.
Source: NOAA NESDIS
Annular modes are immense cyclones spun up over the poles by planetary rotation. Imagine seesawing masses of frigid air spinning off high latitudes. Where it meets warmer moist air it rains. Coriolis force spins up gyres in all the world’s oceans. The oscillations are ocean sea surface temperature modes. Data collected with more method than madness since the 1860’s.
This newish temperature index of Pacific Ocean states shows the warm V and cool surrounds of a warm state. Over the Pacific hot spot cloud is drying and dissipating adding gargantuan energies to the system. These temperature patterns shift between warmer and cooler irregularly. The developers of the index call it epochs. Based on multiple equilibrium states and sudden shifts – more likely evolving patterns in spatio-temporal chaos. This pattern has profound effects on global weather and climate.
Epochs triggered by changes to Earth system boundary conditions. As far as I can tell the limits to climate change are some -10 and +12 degrees C. In as little as a decade in some places. Low summer Northern Hemisphere insolation and a cooler north Atlantic with glacial ice sheet growth. Or cloud evaporating away. The answer to this problem in fluid dynamics is literally incalculable.