This is a concept that I have struggled with a lot over the last few years, and I still haven't found a good answer. To me, the absurdity (or futility, which is the term I prefer, as did Tolstoy) of life is not in the short length of a human lifespan (although that is an additional reason), but in the finite nature of our universe. We now know with a high degree of certainty that our inhabitable universe is finite, and one day all of the energy of the universe will be spent, exhausted, and cease to function. This is an outcome we cannot currently reconcile or outrun. Ergo, there WILL come a day that no matter what humans have endeavored to achieve, it will be washed away by the entropic heat death of the universe, and any outcome will be eternally useless. And if we have prior knowledge that there will come a day when all prior action is rendered meaningless, and no further action can take place, then can action really have meaning in the present?
I don't think that it can.
I just cannot absolve myself of the knowledge that the importance of 'now' will most certainly be rendered irrelevant one day, retroactively robbing the present of whatever worth it has.