Climate change and cities

Climate change and cities are deeply connected. Cities are one of the greatest contributors and likely best opportunities for addressing climate change.^[2] Cities are also one of the most vulnerable parts of the human society to the effects of climate change,^[3] and likely one of the most important solutions for reducing the environmental impact of humans.^[4][2][3] The UN projects that 68% of the world population will live in urban areas by 2050.^[5] In the year 2016, 31 mega-cities reported having at least 10 million in their population, 8 of which surpassed 20 million people.^[6] However, secondary cities - small to medium size cities (500,000 to 1 million) are rapidly increasing in number and are some of the fastest growing urbanizing areas in the world further contributing to climate change impacts.^[7] Cities have a significant influence on construction and transportation—two of the key contributors to global warming emissions.^[8] Moreover, because of processes that create climate conflict and climate refugees, city areas are expected to grow during the next several decades, stressing infrastructure and concentrating more impoverished peoples in cities.^[9][10]

High density and urban heat island effect are examples of weather changes that impact cities due to climate change. It also causes exacerbating existing problems such as air pollution, water scarcity, and heat illness in metropolitan areas. Moreover, because most cities have been built on rivers or coastal areas, cities are frequently vulnerable to the subsequent effects of sea level rise, which cause flooding and erosion; these effects are also connected with other urban environmental problems, such as subsidence and aquifer depletion.

A report by the C40 Cities Climate Leadership Group described consumption based emissions as having significantly more impact than production-based emissions within cities. The report estimates that 85% of the emissions associated with goods within a city is generated outside of that city.^[12] Climate change adaptation and mitigation investments in cities will be important in reducing the impacts of some of the largest contributors of greenhouse gas emissions: for example, increased density allows for redistribution of land use for agriculture and reforestation, improving transportation efficiencies, and greening construction (largely due to cement's outsized role in climate change and improvements in sustainable construction practices and weatherization).