Some CO₂ in the atmosphere is good. It allows heat from the sun to stay on and around the Earth instead of bouncing back into space. Without natural carbon dioxide and other gases to retain solar heat, the planet would be a lifeless snowball—all ice and no skiing. But the Environmental Protection Agency estimates that since the industrial age began, atmospheric CO₂ has increased 30 percent and the concentration of methane, another greenhouse gas, has more than doubled. Without new emission controls, some experts estimate that carbon dioxide concentrations will increase by up to 150 percent above today's level by 2100.