Although solar activity is declining as the Sun approaches solar minimum, a series of large solar storms occurred in September 2017 that impacted both Earth and Mars. This was the largest event seen on the surface of Mars by the Radiation Assessment Detector (RAD) on the Mars Science Laboratory (MSL) Curiosity rover since landing in 2012, and was also observed as GLE72 on Earth, making it the first event observed to produce a Ground Level Enhancement (GLE) on 2 planets at the same time. We present RAD observations of the surface radiation environment since 2012, and discuss the impact of the September 2017 events on this environment, and its implications for human exploration and for mitigating the risk of space radiation and space weather events for future manned missions to Mars.