In sum, it means that a complex of thoughts (memeplex) determine for us the future in which we will live ... leaving us to self-persuade ourselves of the inevitability of this future!
From the point of view of presentism fate would be the trajectory that an entity operates in space time under the effect of determinisms.
Outside it's Exponential economism and are material addiction technologism as the most effective short-term process to dispel the energy that has emerged as the dominant way of thinking.
Therefore, to speak of the destiny of humanity is somewhat amusing, since in such a scenario, our destiny is to be replaced by host more efficient than us.
Our destiny in such a case would be to finish the process of terraforming (what is global warming according to you?) Before disappearing ...
the final energy of the universe will eventually be zero. Only in the form of photons lost in the cold infinity without the possibility of drawing this energy lost forever "in this universe determined by its cosmological parameters".
The energy level of the universe will be exactly the same at the beginning as at the end, it is its distribution in space in view of the expansion of the universe that will vary considerably.
The scenario of Big Freeze you are referring to is only one of many hypotheses, the most coherent model (resulting from quantum gravity) is more in line with Big Crunch / Big Bounce / Big Bang, ie a universe in constant redefinition.