Replacing cement and steel in urban construction by wood could avoid greenhouse gas emissions from cement and steel production and turn buildings into a carbon sink, the Potsdam Institute for Climate Impact Research in Germany (PIK) announced on Monday.  Depending on the scenario, between 10 million tons and close to 700 million tons of carbon could be saved every year, according to a PIK study.  Although global carbon emissions amounted to around 11,000 million tons every year, PIK noted that a "shift to timber would make quite a difference for achieving the climate stabilization targets ...