CCFL-lit LCDs are so inefficient compared to modern LED-lit LCDs that you’ve probably spent enough more on electricity by now to have bought a more efficient monitor.
I can’t speak to the environmental impact, though. Producing the new monitor emitted some amount of CO2, and powering each monitor takes some amount of CO2 per unit time. At some amount of use, the newer monitor will have lower lifetime CO2 generation than your old monitor.