This is a case where both are grammatical, but express different concepts.
The past tense gives the sense that the efforts are in the past; there were specific efforts made, "my efforts" refers specifically to those efforts, and those efforts are no longer existing. An example would be "I tried to find the travel option with the smallest carbon footprint when I traveled to my relative's wedding". Travelling to the wedding was a one time thing that happened in the past, so past tense would be appropriate.
The present tense gives the sense that the efforts still apply in the present. This could be because the efforts are ongoing, still possible, etc. An example would be sorting recyclables out of the trash. If you are still currently doing this, then the present tense is appropriate. Even if you currently aren't doing it, one can still speak in the present tense of the effectiveness of it, if one treats the discussion as being about the general concept of sorting recyclables, rather than the specific acts that happened in the past.
One issue is whether "my efforts" refers to already determined efforts, or what efforts one does. That is, "My efforts are inadequate" has the primary meaning of "There are particular efforts that I made, and those efforts are inadequate", or it could mean "Whatever efforts I end up making, they will be inadequate". While the present tense can work for either, it works more for the latter.
On....is a prepositional phrase. It often happens in English that tenses in prepositions mix with different tenses in other clauses. The tenses all convey slightly different senses or meaning of times, however. @Accumulation's answer does a very good job of describing these in detail, so I won't duplicate that effort!