Maybe so, but not 573 lbs.
Carbon has a molecular weight of 12 grams. O2 has a molecular weight of 32 grams. Carbon dioxide thus has a molecular weight of 44 grams (12 g of C + 32 g of O2 = 44 g). 573 lbs (260 kg) of CO2 is thus equivalent to 5906 mols (260 kg / 0.044 kg). 70.9 kg of carbon (12 g/mol * 5906 mol) and 189 kg of O2 (32 g/mol *5906 mol) combine to form 260 kg of CO2.
We can thus conclude that the Belgian estimate is based upon the assumption that, during the cremation process, roughly 70.9 kg of carbon goes up in flames. The body of a 100-kg man (like myself) contains approx. 18 kg of carbon. So we must assume that roughly 53 kg of carbon from other sources, including the deceased person's burial clothing, cerements (grave-clothes and shroud), the wooden coffin - but also supplemental fuel to initiate combustion and to keep the fires stoked - are likewise consumed in the process.
In short, about only about one-quarter of the carbon dioxide emissions can be attributed directly to the human body, and the remaining three-quarters from "other sources."
In view of these considerations, it thus appears that the Belgian estimate is actually a rather conservative figure!
Regards,