Different species I belive. Ticks in Texas are differnent from ticks in Ottowa. Most lyme disease in the US is concentrated in the northeast and northern great lakes states and into Canada (though it is spreading over the past few decades).

https://www.cdc.gov/lyme/data-research/facts-stats/lyme-dise...

They seem to be much less active on hot days compared to cooler days in my experience - though I can't say why. I've definitely observed a difference over the years though.

That said, whether it is hotter or cooler doesn't make much of a difference in terms of how you go about your day - you pretty much have to assume you can encounter them regardless.

They are a huge problem in Minnesota as well.

It's the length and depth of cold days in the winter that can potentially limit their breeding populations, is my understanding. So the issue is that more northerly areas are getting much more variance in temperature and lacking long deep consistent cold periods.

Up and down cycles in temperature have always been a thing on the North American continent but climate change has made it even more variable. We will still get places where it gets very very cold but not for the consistent chunks of time it takes to set back tick populations significantly.

TLDR I don't think it's the heat or cold per se but the variance.

And yes climate change is absolutely the prime factor in their spread. Into places where they were not ever a threat before.