By recreating the conditions in the Earths crust that result in diamond growth: pressure, heat, & carbon.
There are two methods of growing diamonds:
1. High Pressure-High Temperature (HPHT)
2. Chemical Vapor Deposition (CVD)
Each process is suited for certain sizes and colours of diamonds. Growing a diamond in a lab setting with abundantly available carbon and renewable energy has a low impact on the environment, with little to no harm towards ecosystems or wildlife.