Government flexibility in creating emissions-reducing policy is critical to assessing long term economic adjustments to climate change. Emissions reductions will require changes in consumer and producer behavior and adjusted spending on emissions technologies in both developing and developed nations. Although developed nations use far cleaner technologies, per capita consumption - and thus emissions - is considerably higher. Many nations have articulated a long term goal of reducing their dependence on fossil fuels, a topic addressed in more depth in the energy section of this webpage. In the U.S. these goals have evolved with time due to changing technologies and different political landscapes. Increasingly attention is being given to the kinds of 'market-based' policy tools promoted by economists, including tradable emissions permits like those that have been successfully used to limit SO2 emissions from coal-burning plants in the US. Similar types of flexible, cost-effective tools are being considered for the control of greenhouse gas emissions. The cost-effectiveness of different actions that could reduce carbon emission has been a topic of intense study by economists. The range of potential actions includes substitutions toward low-carbon or non-carbon energy sources, as well as carbon sequestration in forests. Estimates of the potential and cost-effectiveness of some of these different options vary widely. For example, the potential for sequestering carbon in agricultural soils may be quite limited (based on a number of empirical estimates); and the promise of shifting the "hydrogen economy" as a way to reduce carbon emissions faces many obstacles including cost..