Mid century cooling, global dimming and the PDO?

The independent factor (solar irradiance) is either enhanced or diminished by the oscillation cycles, depending on several conditions. It's likely that the negative arctic oscillation enhanced the decrease in solar irradiation, causing a deeper cooling. It's very much like the tides: depending on coincidence of cycles and independent factors, effects can be greatly enhanced or nearly cancelled. Interesting in your second link: how the ENSO and PDO cycles combine their effects.

I believe the main drivers of Earth's climate are soar activity & the path of the Sun-Earth system through interstellar space. There are dark bands in te galaxy. As the Sun-Earth system wanders about the galaxy's center it passes through these dark bands & they impact the amount of Sun energy that hits the planet. Cooling ensues absent any other effects. The Sun's activity is essential to the amount of solar energy hitting the Earth. The amount of irradiation depends on the Solar cycles as indicated by sunspot activity. I don't recall whether its increased activity that increases the energy flow or increased sunspot activity decreases the energy hitting the Earth. It is irrelevant to the premise that the Earth's climate is due to extra-planetary conditions. Up or down, warm or cool, its all due to elements beyond our control. If AGW affects climate at all it will be minuscule in the face of these far larger & more pervasive phenomena. But of course at the moment there is little grant money to study these. The pursuit of remedies for AGW is a red herring & could be a fatal diversion.