What GM would you pick to save Earth?

But Magnus can play without a board and pieces....
And anyways, this is why I wanted to send the Backyard professor. The aliens would have loved that.
GM Jonathan Rowson could save the planet earth. https://en.wikipedia.org/wiki/Jonathan_Rowson
Although no longer an active player, he is Director of the Social Brain Center of the Royal Society of the Arts in London. His Doctoral Thesis centered on "featured an analysis of the challenge of overcoming the psycho-social constraints that prevent people becoming 'wiser'." His 3 chess books, "Chess for Zebras," "The Seven Deadly Chess Sins," and "Understanding the Grunfeld," helped me overcome some of my psycho-social constraints! Now only if I could become wiser.

.. That would be the one, whom, the '800 pound, gorilla', pays heed to.
HE should learn not to point at squares during a game.

I would renegotiate the time of the match to be in the future, 23 years. I would exhume Fischer's body again, extract some dna, make a Fischer clone, and train him using the finest teachers and software (Kasparov and Carlsen, Anand, Kramnik and So all as teachers) from a very early age, to ultimately meet the alien chess threat, and WIN!
It only makes sense to pick Carlsen. He's definitely the strongest in the world right now, and very possibly of all time taking into account the information, technology, and knowledge he has access to. World Champion, highest rating of all time, World #1 for years. By a measurable margin the best in the world, and would be our best hope to save the planet.
i'd like to reiterate that magnus has the best jokes.