I've read that when global temperature increases significantly, liquid magma can make it's way closer to the surface of earth, causing increased volcanic activity and earthquakes. Is there scientific evidence of this?
Define 'significant' effect. Yes, in principle, both volcanoes and major fault lines can, in some cases, be affected by higher global temperatures. It works like this: higher temperatures cause glacial melt and thermal expansion of seawater, which causes sea level to rise. In ocean sediments and coastal aquifers this raises the hydrostatic pressure, increasing groundwater circulation, and hence providing more 'lubrication' to fault planes, and increasing the seepage above magma chambers. However, the effect is small.