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]

Because of the high density and effects like the urban heat island affect, weather changes due to climate change are likely to greatly effect cities,^[12] exacerbating existing problems, such as air pollution, water scarcity,^[13] and heat illness in the 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^[12] and erosion, and those effects are deeply connected with other urban environmental problems, like 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.^[14] 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).

In the most recent past, increasing urbanization has also been proposed as a phenomenon that has a reducing effect on the global rate of carbon emission primarily because with urbanization comes technical prowess which can help drive sustainability.^[15] Lists of high impact climate change solutions tend to include city-focused solutions; for example, Project Drawdown recommends several major urban investments, including improved bicycle infrastructure,^[16] building retrofitting,^[17] district heating,^[18] public transit,^[19] and walkable cities as important solutions.^[20]

Because of this, the international community has formed coalitions of cities (such as the C40 Cities Climate Leadership Group and ICLEI) and policy goals, such as Sustainable Development Goal 11 ("sustainable cities and communities"), to activate and focus attention on these solutions. Currently, in 2022, there is a deterioration in the progress of the goal. There is limited progress on making cities and human settlements more appropriate to live in Sub-Saharan Africa, Latin America and the Caribbean and the Pacific Island countries. There is fair progress in Central and Southern Asia and Eastern and South-Eastern Asian. However, it has been achieved in Developed countries.^[21]