Two new studies forecast that energy use and carbon dioxide emissions in the U.S. and China will level off by about 2030, even if aggressive measures are not taken to rein in greenhouse gases. The forecasts, particularly for China, contradict widespread predictions that China’s energy use and emissions would continue to soar until at least mid-century. Still, both forecasts indicate that greenhouse gas emissions will remain far above the level that most climatologists say is needed to avert major disruptions from global warming. The China study, conducted by the Lawrence Berkeley National Laboratory in California, forecasts that China’s booming economy and energy use will peak around 2030 to 2035, and then level off afterwards as the demands of increasingly affluent Chinese consumers for goods also reach a peak in the 2030s. The rise of nuclear power, coupled with aggressive energy efficiency policies and the spread of renewable energy technologies and electric cars, will help soften demand for fossil fuels even as the Chinese economy grows, the report said. In the U.S., the Energy Information Administration said that even in the absence of measures to curb greenhouse gases, CO2 emissions will grow slowly over the next two decades, not returning to 2005 levels until 2027.