Translate the following English sentence to French:
"On the basis of the experience gained over the past eight years, an attempt is being made to increase the effectiveness of action on behalf of the environment in the third development phase of that financial instrument."
Sur la base des expériences acquises au cours des huit dernières années, ce qui est recherché consiste à accroître l' efficacité des actions en faveur de l' environnement à la phase III de la mise en uvre de cet instrument financier.