Because water is essential to our survival, we are generally aware of the importance of saving this natural resource and of monitoring our day-to-day usage of it. But people are generally much less aware of the need to preserve sand, the second most exploited resource after water, and one that’s also essential to withstanding climate change. Some 50 billion tons of sand and gravel are used in the world every year. This amount of sand would be “enough to build a wall 27 meters wide and 27 meters high around planet Earth,” estimates a new report from the United Nations Environment Program (UNEP)…