Carbon Positive: The US Congress has stepped on to uncertain ground over land-based carbon offsets in its landmark cap-and-trade bill, passed in the House of Representatives last week. Hasty eleventh-hour negotiations saw its proponents embrace temporary carbon offset credits for domestic forestry and agriculture. It’s an approach that has proven unworkable internationally after the unhappy experience of temporary CERs in afforestation and reforestation in the UN Clean Development Mechanism …