We synthesize results from many studies to review how California grasslands may respond to changes in the atmosphere and climate. Biomass production in these grasslands is not highly responsive to increases in atmospheric CO₂, small increases in temperature, or increases in winter precipitation. Rather, changes in the length of the rainy season would be more likely to affect production, as would increases in nitrogen deposition. Species compositional changes may be more dramatic than changes in production, but are also generally more difficult to predict due to the specificity of responses and the relatively high number of species in California grasslands. Studies to date have largely focused on changes that might occur within the current vegetation type. Non-native species and native woody species, however, may have the opportunity to enter and spread under new climate and atmospheric regimes, which might lead to greater changes in the functioning of the ecosystem. Model simulations suggest that changes in fire regime could strongly promote or constrain any shifts in vegetation types. Climate change could thus lead to shifts in vegetation by altering fire regimes.