Tropical forests host a rich diversity of plant and animal life and process vast amounts of carbon dioxide (CO2). Therefore, researchers have been particularly interested in how these ecosystems might be affected by climate change. Some have hypothesized that the rise in atmospheric CO2 is promoting carbon uptake by these forests, making them important carbon sinks. Evidence is mounting, however, that the balance of cost and benefit is reaching a tipping point, and global warming will soon hinder tropical forests' ability to soak up carbon.