Question: What is the 100 year for Carbon dioxide?
SQL: SELECT "100-yr" FROM "1-21350772-2" WHERE "Gas name" = 'Carbon dioxide';

Question: What is the 20 year for Nitrous oxide?
SQL: SELECT "20-yr" FROM "1-21350772-2" WHERE "Gas name" = 'Nitrous oxide';

Question: What is the lifetime (years) for chemical formula CH 4?
SQL: SELECT "Lifetime (years)" FROM "1-21350772-2" WHERE "Chemical formula" = 'CH 4';

Question: What is the 500 year where 20 year is 289?
SQL: SELECT "500-yr" FROM "1-21350772-2" WHERE "20-yr" = '289';

Question: What is the 100 year when 500 year is 153?
SQL: SELECT "100-yr" FROM "1-21350772-2" WHERE "500-yr" = '153';

Question: What is the 20 year for Sulfur hexafluoride?
SQL: SELECT "20-yr" FROM "1-21350772-2" WHERE "Gas name" = 'Sulfur hexafluoride';