The Atmosmare Foundation still considers carbon sequestration in trees grown to large sizes to be the cheapest and most cost-effective way to remove carbon from the atmosphere. However, carbon sequestration in growing trees has become more difficult in many parts of the world due to the warming that has already occurred.
Forests in many northern countries have turned from carbon sinks into sources of carbon emissions due to destructive insects, more intense storms, and forest fires. Half of the Amazon rainforest also appears to have become a source of carbon emissions due to severe drying in the region.