It may be only a temporary thing.. while the Global Warming is going on.
The general increased heat is because the earth getting closer to the sun.
The reason: is the continuous loss of the earth central heat leading to the sun's gravity effect on the earth becoming greater than before.
So although the sun is also losing heat, but the relative loss of the earth heat is more, and the earth center becoming colder than before, while the Global Heat is more on the surface.
The effect of the increased heat on the earth surface is negligible in relation to the loss of the earth central heat (by volcanoes and radiation): this will lead to:
1- the earth becoming slower in spinning around itself.
2- the gravity of the sun will influence it more and will pull the earth to be nearer to it gradually.