Christian Science Monitor: Forecasting climate change is like assembling a jigsaw puzzle when you don’t know its overall pattern. Sometimes you find a piece you didn’t even know was missing. A discovery that arid deserts may be soaking up a lot of carbon dioxide is a case in point. And other times you see a puzzle piece in a helpful new perspective. That has just happened in a study of how nitrogen fixation affects the CO2-absorbing capacity of forests. The latter takes some explaining. It involves subtleties …