What causes the convection currents in the mantle?

Extensive and unusual cold snaps have occurred here recently. is this evidence that global warming is lessening or not occurring? no—although the long-term trend is for warming, short-term weather patterns can still be variable. no—melting of glaciers and ice caps is making the oceans cooler, which can cause cold snaps. yes-- if global warming really were occurring, cold snaps wouldn’t happen. yes—due to global warming, weather patterns should be become less—not more—variable.