The version of global warming theory being pushed by the IPCC is that anthropogenic emissions of greenhouse gases are causing a radiative energy imbalance of the climate system, leading to warming.
The radiative forcing history being used in the latest IPCC climate models looks something like the following, with red areas representing times when the climate system’s “stove is turned up”, that is, with heat accumulating in the system.
(Actually, the correct analogy would be that the stove setting remains the same, but the lid partially covering the pot is covering it a little more over time…but that’s too hard to explain.)
As can be seen, in the last 10 years the estimated forcing has been the strongest. Yet, most if not all temperature datasets show little or no global-average warming recently, either in the atmosphere, at the surface, or in the upper 700 meters of the ocean. For example, here are the tropospheric temperatures up though a few days ago:
So what is happening? You cannot simply say a lack of warming in 10 years is not that unusual, and that there have been previous 10-year periods without warming, too. No, we are supposedly in uncharted territory with a maximum in radiative forcing of the climate system. One cannot compare on an equal basis the last 10 years with any previous decades without warming.
There are 5 possibilities for the recent cessation of warming which are most discussed:
1) cooling from anthropogenic aerosols has been cancelling out warming from more greenhouse gases
2) natural cooling from internal climate fluctuations or the sun is cancelling out the GHG warming
3) increased ocean mixing is causing the extra energy to be distributed into the deep ocean
4) the temperature ’sensitivity’ of the climate system is not as large as the IPCC assumes.
5) there is something fundamentally wrong with the GHG warming theoryitself
Of course, some combination of the above 5 explanations is also possible.