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Human overpopulation and the way we use our land, energy, food and water are the drivers of climate change, ecosystem degradation, and biodiversity loss. As humans, we have control of these drivers and our major decision points and policies are aboout these drivers.

Public health is affected by the consequences of our decisions at the individual, community and global levels.

Our ability to develop policy responses to these issues will be complicated by three additional challenges:

• Energy scarcity, due to geologic, political, or policy considerations
• Debt as an obstacle to new investment
• Obstacles to policy change

Concern about energy scarcity is part of the complex dynamics of the energy system. The world has likely passed the peak of conventional petroleum production. Global society has decided that a constant supply of fossil fuels, especially petroleum, is more important than a stable climate. The supply of petroleum is now being maintained by unconventional fossil fuel extraction (including by hydraulic fracturing, also know as “fracking”), with more dire consequences for the climate and many heretofore poorly characterized environmental and health impacts. The amazing success around the world in unconventional fossil fuel supply growth has resulted in energy prices that are quite low, contributing to more use and more climate impacts. Over the longer term, it is likely that prices for fossil fuels will rise, making the transition to more sustainable energy sources considerably more difficult, yet more urgent. Read more about the connections between the energy system and the food system.

In addition, sustainable responses to climate change and energy transitions will require large investments in research and development, building new infrastructures, and community re-design at a time when debt is an obstacle to new investment. U.S. federal indebtedness is at an all-time high (see ""). Many analysts have argued that changes on the required scale will not occur until the U.S. government makes the necessary investments.

Finally, obstacles to policy change include the short-term horizon of many elected officials, the influence of money in our political system, the recent decreasing role of science in policy making and the fact that many of the required changes will be unpopular with the electorate.