Also, the onset of glaciation or deglaciation appears to be triggered by orbital effects that have big seasonal / regional impacts but apply almost zero RF in the global mean. (realclimate.org)
The two principal mechanisms by which the orbital effects on the regional / seasonal distribution of insolation instigate climate change are melting / growth of ice sheets (thus albedo change — > temperature change) and the slow feedback effect of GHGs responding to temperature change, thus increasing the greenhouse effect. (dotearth.blogs.nytimes.com)
This is an issue because we know there is a substantial long - term natural cooling trend for high - latitude summers because of Earth orbital effects, but the trend is nearly zero in the global annual average. (dotearth.blogs.nytimes.com)