Main climate threat from CO2 sources yet to be built

Scientists have warned that avoiding dangerous climate change this century will require steep cuts in carbon dioxide emissions. New energy-efficient or carbon-free technologies can help, but what about the power plants, cars, trucks, and other fossil-fuel-burning devices already in operation? Unless forced into early retirement, they will emit carbon dioxide into the atmosphere for decades to come. Will their emissions push carbon dioxide levels beyond prescribed limits, regardless of what we build next? Is there already too much inertia in the system to curb climate change?