Why are carbon dioxide and methane (among other elements) constantly cited as the major cause for warming but natural occurrences such as El Nino and La Nina are cites as the cause for why warming has slowed down or stopped?
Because they are different classes of elements.
ENSO is a pseudo-cyclical process that significantly affects the transport of heat on Earth. The changes they make as to where the heat goes has direct effects (droughts, storms, weather pattern changes, ocean temperature profiles, etc) and may possibly affect the amount of heat that radiates to space. For example, suppose one phase of the cycle moved heat from the deep ocean to the upper atmosphere. More of that energy could find its way to space. On the other hand, suppose another phase of that cycle was doing the opposite: moving heat energy from the atmosphere to the deep ocean. Less of that energy would get the chance to reradiate away from the planet. If, as BTK 2013 suggests, thermal energy is being sequestered in the deep ocean and thus the temperature of atmosphere is not rising as quickly as it formerly had done, the net result may be WORSE for us in the long run. But I have wandered off the point.
GHGs are responsible for trapping solar energy in the Earth's atmosphere. That would happen whether the Earth's atmosphere was utterly motionless or was boiling like a forgotten pot on the stove. ENSO is one of the multiple processes that move the climate's energy about. It will effect some control over where that trapped heat goes. If it puts it in the ocean and makes it unavailable (for the nonce) to heat the atmosphere, we will not feel it getting warmer. Thus, when I say we will have to wait for the LaNina/negative PDO to cease, I do not say that those processes are the source or the sink of our warming. They are just one of the dealers shuffling the deck.
