What causes a star to be blue or red-shifted?

Redshift and blueshift describe how light shifts toward shorter or longer wavelengths as objects in space (such as stars or galaxies) move closer or farther away from us. ... If an object moves closer, the light moves to the blue end of the spectrum, as its wavelengths get shorter.

burning of wood and coal

explanation:

the panel also concluded there's a better than 95 percent probability that human-produced greenhouse gases such as carbon dioxide, methane and nitrous oxide have caused much of the observed increase in earth's temperatures over the past 50 years.