Effects of a different CMBR temperature?

[malloyd]

Originally Posted by vicky_molokh

IOW, even if you raise it to 30K or even 100K, this will have zero noticeable effect on planetary climates?

Well for terrestrial planets. It may matter for iceballs. It's much the same issue as the second stars of binary systems usually don't matter for the habitable planet's temperature.

Two temperature sources add as the fourth root of the sum of their fourth power. So if you have two sources that would heat something to 100K in isolation, their combination heats the thing to 119K, which could matter, but if you have a one source that heats it to 300K and add another that would heat it to 100K, the combination heats it to 300.9K, which is likely negligible.

Edit: Is there a goal here? If you want a setting where space happens to be warm, I wouldn't suggest tampering with cosmology. Look for an excuse to bathe the entire region of the setting in a hot gas cloud instead. Yeah it's a little tricky to justify why whatever heated a cloud light-years across didn't kill everything in the region, but you can probably come up with something. If another galaxy collided with the Milky Way you might be able to get a jet of gas getting tossed off in the direction of one of the Magellanic Clouds that would still be fairly warm when it got there with less handwaving than changing the expansion of the universe. Sure it'll pass through, or cool back down again in 10 or 100 million years, but your metaplot doesn't need that much time anyway, right?