Intriguing question! I've not come across any study that quantifies the contribution from Geothermal sources to global warming for the entire Earth. So I'm all ears for expert opinion.
Cyril, do you have a specific geological time period in mind or do you mean in general during the present time? As far as I understand, the Earth was much warmer (As hot as Hades!) in the geological past, and contributions from geothermal sources may have been considerable back then.
The heat flux from interoir of the earth does affect the earth's climate to certain extent, in the forms of volcanic eruptions, seafloor hot water vents (black chimney) and so on. However, these are not neccesarily heat from the outer core of the earth spefically.
Hope this helps, good luck!
As opined by Zhonghe Pang, heat from the outer core does not directly cause global warming but the rate of flow of geothermal energy across the surface from interior warms up the earth's climate.
Currently observed global warming is not enhanced by changes in heat flow emanating from the outer core of the earth.