In the USA, a sizable share of the population denies the human causes of climate change and opposes policies to address it. System justification, where individuals fight to protect a socio-economic order, undergirds this opposition. We argue that sexism, representing an investment in gendered hierarchies, contributes to climate change denial and policy opposition. Using nationally representative surveys from 2016 to 2018, we show a consistent relationship between sexism and opposition to climate change beliefs and policies. These results are consistent across measures of both climate change beliefs and support for climate policy. We then show that sexism is correlated with climate denial and opposition to climate policy within a wide variety of subgroups of interest: for both Democrats and Republicans and for groups sorted by ideology, gender, education, and age. We then extend our analysis back in time, looking at data from 2012, finding similar effects prior to the 2016 election. The consistent findings point to the central role that system justifying beliefs about gender play in shaping attitudes about climate change in the USA.