Dyson agreed that technically humans and additional CO emissions contribute to warming. However, he felt that any such contribution was minor relative to natural effects and that the benefits of additional CO outweighed any associated negative effects. He said that in many ways increased atmospheric carbon dioxide is beneficial, and that it is increasing biological growth, agricultural yields and forests. He believed that existing simulation models of climate change fail to account for some important factors, and that the results thus contain too great a margin of error to reliably predict trends.