Do you run your home server 24/7? If you do, you are probably wasting a whole bunch of CPU cycles and energy. There’re plenty of technology available to reduce carbon, for e.g. on AMD powered WHS, you can enable AMD’s Cool‘n’Quiet technology in the BIOS to reduce energy footprint, but that would still left wasting a bunch of CPU cycles.
So what does all that have to do with CPU cycles? Well, that is exactly what BOINC was designed to do. It runs in the background and makes use of those otherwise wasted CPU cycles. And for a good cause. For those who may not be aware of BOINC:
“Use the idle time on your computer (Windows, Mac, or Linux) to cure diseases, study global warming, discover pulsars, and do many other types of scientific research. It's safe, secure, and easy.“
More info: BOINC