Question: which geoengineering method for carbon sequestration has been enacted for several decades
[{'answer': 'Carbon dioxide removal', 'provenance': [{'wikipedia_id': '2119179', 'title': 'Climate change mitigation', 'start_paragraph_id': 13, 'start_character': 371, 'end_paragraph_id': 13, 'end_character': 393, 'bleu_score': 1.0, 'section': 'Section::::Greenhouse gas concentrations and stabilization.\n'}]}, {'provenance': [{'wikipedia_id': '2119179', 'title': 'Climate change mitigation', 'start_paragraph_id': 106, 'start_character': 0, 'end_paragraph_id': 106, 'end_character': 459, 'bleu_score': 0.9712154609069981, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 1958336169432515975}, 'section': 'Section::::Methods and means.:Geoengineering.:Carbon dioxide removal.\n'}]}]