2014’s Mars Evacuees is the first of two volumes in Sophia McDougall’s Mars Evacuees young-adult military SF series.
The Morrors appeared from deepest space to save humanity from unchecked global warming, in return for which they asked only minor territorial concessions. Merely in the coldest regions of Earth. Well, they demanded rather than asked and their territorial demands were major rather than minor. Since the Morrors required more arctic territory than existed at their arrival, they set about cooling the entire Earth to better suit their needs.
For the last fifteen years, longer than Alice Dare’s entire life, humanity has been fighting a losing battle against the aliens.