a sustainable reliance on the surrounding natural environment and the ability to power itself with renewable sources of energy, while creating the smallest conceivable ecological footprint and the lowest quantity of pollution achievable. All of this is to be accomplished by efficient land use, composting organic matter, recycling used materials, and/or converting waste-to-energy. The idea is that these contributions will lead to a decrease of the city's impact on climate change. Today, 55 percent of the world is estimated to be living in urban areas and the United Nations estimates that by the year 2050, that number will rise to 70 percent. By 2050, there may be nearly 2.5 more billion individuals living in urban cities, possibly making it more difficult to create more sustainable communities. These large communities provide both challenges and opportunities for environmentally-conscious developers. There are distinct advantages to further defining and working towards the goals of sustainable cities. Humans are social creatures and thrive in urban spaces that foster social connections. Richard Florida, an urban studies theorist, focuses on the social impact of sustainable cities and states that cities need more than a competitive business climate; they should promote a great people climate that appeals to individuals and families of all types. Because of this, a shift to denser urban living would provide an outlet for social interaction and conditions under which humans can prosper. These types of urban areas would also promote the use of public transit, walkability and biking which would benefit citizens' health as well as benefiting the environment. Practical methods to create sustainable cities Different agricultural systems such as agricultural plots within the city (suburbs or centre). This reduces the distance food has to travel from field to fork. This may be done by either small-scale/private farming plots or through larger-scale agriculture (e.g. farmscrapers). Renewable energy sources, such as wind turbines, solar panels, or bio-gas created from sewage to reduce and manage pollution. Cities provide economies of scale that make such energy sources viable. Various methods to reduce the need for air conditioning (a massive energy demand), such as passive daytime radiative cooling applications, planting trees and lightening surface colors, natural ventilation systems, an increase in water features, and green spaces equaling at least 20% of the city's surface. These measures counter the "heat island effect" caused by an abundance of tarmac and asphalt, which can make urban areas several degrees warmer