Agence France-Presse: Forests that today soak up a quarter of carbon pollution spewed into the atmosphere could soon become a net source of CO2 if Earth’s surface warms by another two degrees Celsius (3.6 degrees Fahrenheit), cautions a report to be presented Friday at the UN. Plants both absorb and exhale carbon dioxide, but healthy forests — especially those in the tropics — take up far more of the greenhouse gas than they give off. When they are damaged, get sick or die, that stored carbon is …