EcoWatch: Spring is a time of rebirth: blossoms and greenery emerge as cold and snow give way to warmer temperatures and longer days. It can also kick off a season of sneezing, headaches and itchy, watery eyes. Like a growing number of people, Im allergic to tree pollen. Many say their symptoms have worsened over the years. Theyre probably right. Weve upset the Earths carbon cycle by burning fossil fuels and destroying forests and wetlands. Plants help rebalance it by absorbing carbon dioxide and producing...