Lockheed Martin plans to do its part to help curb global warming by bombing the earth with saplings. The company will convert warplanes, initially developed to drop landmines, and use them to bombard the ground with biodegradable metal cones carrying tree shoots. Once the devices hit the ground, they should explode and the trees should take root. The system can be used to plant 900,000 young trees a day. The Massachusetts-based company Aerial Forestation, which is promoting the endeavor, hopes to use the “tree bombs” to reforest the Scottish mountains, part of Germany’s Black Forest, and Egypt’s Sinai desert. The company believes it will get business from polluters who will have to plant trees to offset their carbon-dioxide emissions.