Green subsidies - green first of all is speaking about environmentally friendly, subsidies are incentives, usually provided by a government to promote some sort of beneficial or preferred activity. So here, it is talking about incentives or benefits given [to car manufacturers] to produce more environmentally friendly cars, or making hybrids cheaper to buy. Big plus is slang, meaning that it is a "pro", the pro in pros & cons, for & against. A close Chinese equivalent would be 好处. Decadent - indulgent sounds about right, more specifically it may be describing the dessert as something to be indulged in, to enjoy the pleasure of.