What are hard laws? What are soft laws? What are the costs and benefits of each law in international regime agreements?

What are hard laws? What are soft laws? What are the costs and benefits of each law in international regime agreements? Assessing the benefits and costs of both hard-law and soft-law, which one would you think would be more appropriate for the international environmental regime? Do you think hard law is more suitable in environmental regimes due to the problems of externalities? Do you think soft law is a better choice because of its dynamic nature and potential to learning and accommodate change with time? Elaborate your arguments with examples and theoretical arguments