The bishop on f5 is in the knight's way and it's not easy to break on e5 anymore. One idea that Black has in mind is to capture the knight on d3 and play Nf5 next.
1. c2c4 A natural opening move, but it's hard to say if it's better than the more restrained pawn advance to c3. 1.Nb3 and 1.d4 are good moves as well. 1... c7c6 This is more accurate than copying White's first move. 2. d2d4  2... h7h5 A difficult move. The idea is to play …g7-g6 without White having check on h6 and also move it to h4, restricting the development of White's queen on h1. But perhaps it would be better to fight for the center first. 3. c4c5  3... d7d5  4. h2h4 This is an important move sooner or later, in order to be able to play g3 and develop the queen. 4... e8f6  5. g2g3  5... g7g6  6. a1b3  6... f6g4 Carlsen complicates the game. The knight supports the …e7-e5 break and can go to h6 if attacked. 7. e1d3  7... c8f5  8. f2f3 