It is unknown whether or not Nikola Tesla really invented the time machine, as it has never been found.
Whether or not he invented it, it is certain he was a brilliant inventor, and made advances in the fields of electricity and magnetism. After Einstein published his theory of relativity, Time became easier to experiment with. We now know that time is easier to control the slower you go, however, going past the speed of light is impossible for any known material.
If we assume that time travel is possible, even if only in one direction and even if only for objects with mass less than a photon, then the question of global warming could be solved by sending excess CO2 back in time.
If we were able to travel through both time and space, the possibilities are endless. Unfortunately, it is also impossible with what we know today. Perhaps in a future where man is more intelligent and wiser, such travels will become possible.