The consequences of the impacts of asteroids about 1 km in size on the Earth are considered from the viewpoint of their negative effects under conditions when the climate changes. These effects are ejection of greenhouse gases, fires, changes in surface albedo, and global dispersion of asteroid material. Estimates show that the impacts of this size do not pose a direct threat of climate change, however, they can lead to substantial damage. Dispersion of iron contained in asteroids over the ocean surface can have a strong influence on the ecosystem (development of phytoplankton, sequestration of carbon dioxide, blooms of toxic algae); but it is not yet possible to predict consequences of ocean fertilization with any assurance.