A major challenge to worldwide sustainability is finding a way to meet the ever-growing energy needs of a growing population with increasing economic success and a steadily dwindling supply of resources. Vance, Eason and Cabezas analyze the feasability of incerases energy efficiency and reductions in energy consumption over time to return to the environmental impact levels of the 1970's. Compared to 1977, the global population is expect to double by 2030, causing expected energy demand to increase 150% over 1977 levels. Accompanying the increase in population, global GDP will increase 352%. The world is reaching diminishing returns in energy efficiency, which has become stagnant over the last several decades. Energy efficiency would have to increase 120% if it was the sole method to achieve sustainability for the projected growth. Vance et. al. explore various scenarios to study the practical challenges of energy sustainability. They used the year 1977 resource and impact levels as a representative "tipping point" for sustainability, which served as a baseline for their calculations. Overall energy efficiency was found to not siginifcantly increase over the study time period. they then tested three scenarios, one with "business as usual" using projected values for global growth, a second that reduced energy demand by 2% each year starting in 2014, and the third reducing energy demand by 3% per year beginning in the same year. Changing these parameters allowed Vance et. al. to determine the relationship between energy efficiency and environmental impact as energy demand changes.Vance et. al. incorporate the following principles in their study: (1) Minimize depletion of natural resources, (2) create engineering solutions beyond current or dominant technologies; improve, innovate and invent (technologies) to achieve sustainability. In order to create a more sustainable future, the energy demand must be reduced to conserve resouces, rather than increasing energy efficiency, which increases energy use and consequently energy demand. A sustainable future can be achieved by setting realistic goals on decreasing energy demand to drive it near the biological capacity of the earth. This decrease in demand requires the use of new methods of energy conservation, such as integrated energy systems in processing and power plants. However, we must be careful that we do not fall into the trap of increased use of a resource to reduce the use of another. In addition, policy development and legislation are critical to garner support for these technologies and spur implementation of sustainable approaches in the future. Say we take the first scenario provided by Vance et. al. and want to see how much of an environmental impact increasing efficiency from now until 2030 has on the global population. Assume the population grows at a rate of 2% per year, economic growth is at 4% per year and the increases in techinological efficiency are 0.001% per year. Estimate the impact of these changes.Suppose we reduce our energy consumption by the mentioned 2% per year from now until 2030. Assume this correlates to a 0.003% increase per year of the T in the IPAT equation. Also consider with a 3% energy reduction that the increase is now 0.002% per year as the T in the IPAT equation. Assume the same population and economic growth increases as the previous question. Which of the three cases gives the largest impact?Vance et. al. believe that reducing energy consumption instead of increasing energy efficiency is the better option, based on the values obtained, is this an appropriate conclusion?