by Javier, August 29, 2018 in WUWT
A no-assumptions look at the global warming evidence helps clarify the possibilities.
The planet’s surface has been warming since the depths of the Little Ice Age, and particularly since ~ 1850 AD. The surface temperature record, however incomplete or uncertain, reflects this warming. Hypotheses about why the warming is taking place can be grouped into three general categories:
- The energy input is increasing. This is the basis of the variable solar output hypothesis.
- The energy output is decreasing. This is the basis of the greenhouse gases hypothesis.
- The transfer of heat within the system is changing. This is the basis of some hypotheses for a reduced vertical exchange in the ocean, or for changes in the oceanic currents that redistribute the heat.
A combination of these categories cannot be ruled out.
Whatever causes the temperature change must necessarily affect its rate of change, the velocity at which temperature changes over time, measured in °C/decade. A velocity that varies continuously and can be positive (warming) or negative (cooling).
Figure 1. 9-year global surface temperature rate of change (4-year averaged) in °C/decade. The Pause is indicated by the khaki box. Source: Met Office UK, HadCRUT 4.