Does this mean that the current observation of rise in sea level due to global climate change is due to dark matter annihilation ?
Of course not. This has nothing to do with climate change (this was the clickbait part of the post :D ).
The point is that dark matter can contribute to the heat flow originating from Earth. We have measured this heat flow. Thus we can constrain the properties of dark matter.
Okay. I got it. Dark matter was always being annihilated inside the earth through out it's history. Hence we can't attribute the recent observation of the rise in temperature to the dark matter annihilation. But what if suddenly earth is being hit by more dark matter than usual ?
No we can't. There are models, for which dark matter can be captured by Earth and annihilate inside it. In this case (and only for those models), there is a heat flux that is generated. This contribute to the total heat outcome of the planet (that we know with some precision) and we must only make sure that there is no inconsistency with the observations.
Does it clarify?
We can estimate the local density of dark matter. There is no way this can suddenly change without messing up the entire cosmology.