We have examined the effects of ozone precursor emissions and climate change on the tropospheric ozone budget. Under RCP 6.0, ozone in the future is governed primarily by changes in nitrogen oxides (NOx). Methane is also important, and induces an increase in tropospheric ozone that is approximately one-third of that caused by NOx. This study highlights the critical role that emission policies globally have to play in determining tropospheric ozone evolution through the 21st century.