  In this note we address the worldsheet description of 4-dimensional N=8
supergravity using ambitwistors. After gauging an appropriate current algebra,
we argue that the only physical vertex operators correspond to the N=8
supermultiplet. It has previously been shown that worldsheet correlators give
rise to supergravity tree level scattering amplitudes. We extend this work by
proposing a definition for genus-one amplitudes that passes several consistency
checks such as exhibiting modular invariance and reproducing the expected
infrared behavior of 1-loop supergravity amplitudes.
