Despite the absence of a time series for Martian global temperatures, K. I. Abdusamatov has proposed that "parallel global warmings" observed simultaneously on Mars and on Earth can only be a consequence of the same factor: a long-time change in solar irradiance."[73] While some climate change skeptics take this as proof that humans are not causing climate change, Abdusamatov's hypothesis has not been accepted by the scientific community. His assertions have not been published in the peer-reviewed literature, and have been dismissed by other scientists, who have stated that "the idea just isn't supported by the theory or by the observations" and that it "doesn't make physical sense."[74] Other scientists have proposed that the observed variations are caused by irregularities in the orbit of Mars or a possible combination of solar and orbital effects.[75]