Klaus Lackner and Allen Wright, senior staff associate at the Lenfest Center, are developing artificial trees that will pull carbon dioxide from the air, just as real trees do. Their air capture machines are like giant filters that trap the carbon dioxide, which can later be freed and compressed to liquid carbon dioxide. Together with water and energy the carbon dioxide can be used as feed stock for synthetic fuels. Another alternative would be to safely sequester it deep below the Earth’s surface. On a smaller scale, Lackner and Wright recently demonstrated how the technology can be used to supply carbon dioxide to greenhouses to maintain healthy plant growth. The filters pick up carbon dioxide in the outside air when dry; then release it when exposed to the damp, humid conditions found in a greenhouse.