—The preceding unsigned comment was added by  (talk • contribs) .

Carbon at ambient pressure does not melt but sublimates. A liquid phase only exists above 10 MPa.  

If we don't restrict this to elements and allow compounds, there's tantalum hafnium carbide (Ta4HfC5) with a m.p. of 4215 °C . (Note though that even Britannica weasels around calling it "the" highest.)