Green technology innovations, urban innovation environment and CO2 emission reduction in China: Fresh evidence from a partially linear functional-coefficient panel model

•We use a partially linear function-coefficient model to explore the nonlinear moderating effect of the urban innovation environment on the impact of green technology innovation on carbon dioxide emissions.•There are heterogeneous impacts of green technology innovations on CO2 emissions in different periods and different types of cities.•Green technology innovation can reduce CO2 emissions indirectly through industrial structure upgrading.•Government fiscal expenditure cannot significantly impact the CO2 reduction effect of green technologies.•The effect of green technology innovations on CO2 emissions is only significant when the human capital level of a city has reached a certain level. Green technology innovations have a better carbon emission reduction effect in cities with higher human capital levels.