evidence: Multiple independent lines of evidence indicate that the present-day increase in atmospheric CO2 is caused by human emissions from fossil fuels and land use change. A significant fraction of annual CO2 emissions remains in the atmosphere each year and has steadily accumulated since the onset of the industrial era, driving global warming. Ocean temperature-CO2 feedbacks are important in millennial-scale glacial-interglacial transitions but do not explain the current atmospheric CO2 increase.