Climate change is the rule rather than the exception. It is constantly changing regionally even while remaining generally stable globally. Genetic drift is one of the big movers of evolution. A population has many individual differences, some of which may be beneficial in a dry climate to the extent that more individuals with that variation survive and reproduce during a drought. The population as a whole will drift in that direction.
We’ve got climate change over short or long periods of time regionally in many parts of the world. Desertification in East Africa had its influence on human evolution.
Good point - I should have included human-generated CO2 driven climate change. (That is what the watermelons always infer with climate change, not natural transition or variation.)
As for population genetics and selection pressure, I am familiar with this topic. Selection pressure changes the frequency of alleles in the population. These alleles are all part of the species’ gene pool. It is hardly evolution. It, in no way, contributes to speciation.
You are not saying that small temperature changes or atmospheric humidity increases increase mutation frequency, are you?
Sickle cell anemia is a classic example of a mutation that changes frequency based on environment/selection pressure - it is beneficial in fighting malaria. - But Malaria did not cause the sickle cell allele to come into being. That thought is Lamarkian.