OPEC nations argued on Friday that a final international accord on climate change should include a plan to compensate them in case efforts to cut greenhouse gases lead to a drop in the use of oil. “We are assuming that only for another 15 years, maximum, will we have oil as a big share of the energy mix,” said Muhammad al-Sabban, head of the Saudi delegation, at talks in France last week leading up to a major climate change meeting that will take place at the Hague in November. China and many other developing nations backed the OPEC position, while other participants panned it. Opinions are also split on a U.S. plan for countries to receive credit for reducing greenhouse gases by growing trees to absorb carbon dioxide. The U.N.’s top official on climate change, Michael Zammit Cutajar, said Friday he believed countries should accept the use of forests as carbon sinks and endorse emissions trading between countries as a way to tackle global warming, assuming a firm emissions accounting system were put in place.