<p><P>PROBLEM TO BE SOLVED: To provide a method for promoting the photosynthesis of photosynthetic organisms, excellent in handling properties, using a CO<SB POS="POST">2</SB>carrier which is high in CO<SB POS="POST">2</SB>absorption, and has CO<SB POS="POST">2</SB>releasing properties, and usable for reduction the amount of CO<SB POS="POST">2</SB>derived from a small-scale disperse type emission source. <P>SOLUTION: This method for promoting the photosynthesis of photosynthetic organisms includes a CO<SB POS="POST">2</SB>absorbing process of producing a CO<SB POS="POST">2</SB>carrier by making swelling gel which includes an element shown by following general formula (1) (in the formula, R shows a hydrogen atom or 1-4C alkyl group) absorb CO<SB POS="POST">2</SB>, and a CO<SB POS="POST">2</SB>releasing process of suppl
