The Urban Paradox: Why Global Cities Struggle to Achieve Sustainable Development

Global urbanization is undergoing a profound imbalance. In 2022, the world population reached 8 billion, with more than half residing in cities; by 2050, this proportion will rise to 70%. However, the pace of urban expansion has already far exceeded the carrying capacity of housing, transportation, and public service systems. A brutal symbolic fact is that cities occupy only 3% of the Earth's land, yet consume 60% to 80% of global energy and produce 75% of carbon emissions. The modern civilization that humanity takes pride in is burning at an unsustainable rate in a concrete jungle.

Why has the urbanization dividend become a structural deficit

Cities should have brought opportunity and efficiency. But in many developing countries, urbanization is far outpacing infrastructure development, leading to the spatial entrenchment of poverty and inequality. According to the latest UN data, about 3 billion people worldwide cannot afford decent housing, and 1.12 billion live in slums or similar conditions lacking clean water, sanitation, and stable electricity. Worryingly, new urban residents are mainly flowing into small cities and medium-sized towns, which are precisely the places most lacking in planning capacity and financial resources, thus falling into a vicious cycle of "growth—scarcity—further growth."

Public transportation is a barometer of this structural imbalance. By 2022, only about half of urban residents worldwide had convenient access to public transport. In low-income countries, this proportion is even in the single digits. For vulnerable groups, inaccessible transportation means not only commuting difficulties but also the systematic deprivation of opportunities for education, healthcare, and employment.

Climate crisis: Urban exposure and vulnerability

Cities often perceive climate change more acutely than rural areas. High population density, strong heat island effects, and concentrated infrastructure magnify the impact of extreme weather. According to the United Nations' 2025 Sustainable Development Goals Report, by 2040, more than 2 billion urban residents globally may experience an additional temperature rise of at least 0.5°C; by 2050, 36% of the global urban population will face environments with annual average temperatures above 29°C. Flood risks are also becoming increasingly severe. In 2025, 1 billion people worldwide live in areas highly susceptible to severe river flooding, about half of them in cities. From the sinking of Jakarta to the flooding of New York subways, cities appear exceptionally fragile in the face of global warming.

This is no accident. Historically, many cities were built along rivers, coasts, and deltas for trade and water transport convenience; but today, these geographic advantages are turning into climate risk exposure. Without accelerated investment in resilient infrastructure and disaster early warning systems, the human and economic losses from extreme weather will only become more devastating.

From disorderly growth to conscious governance

The root of urban plight lies in governance failure. For decades, many cities have relied on the path of "organic sprawl," lacking comprehensive land use planning, transit-oriented development, and public space provision. The expansion of slums, the normalization of traffic congestion, air pollution, and the disappearance of green spaces all point to the same problem: urban growth has not been incorporated into the track of sustainable development.2015年通过的可持续发展目标11（SDG 11）试图扭转这一局面。目标涵盖11个子项，从“确保人人获得适足、安全和负担得起的住房”到“提供安全、可负担、无障碍的交通系统”，再到“加强包容和可持续的城市化”。同年通过的《巴黎协定》和2016年的《新城市议程》进一步形成共识：城市治理必须从被动应对转向主动设计。

一些城市已开始提供解题思路。西班牙巴塞罗那推广“超级街区”模式，将若干街区的机动车交通移入周边干道，释放出步行与绿化空间，从而降低噪音与空气污染；法国巴黎提出“15分钟城市”，鼓励居民在步行或骑行范围内满足生活所需；基加利通过推动社区参与式土地登记和微型升级，让非正规住区的居民获得基本服务与产权保障。这些实践未必可以在所有地方复制，但都指向同一个方向：城市更新不能只依靠大型项目，必须从社区尺度嵌入日常治理。

每个人都是城市转型的参与者

在宏观政治与金融资本之外，城市居民是可持续转型最容易被忽视的力量。SDG 11的实现，要求公民对所在街区、建筑和公共空间形成明确愿景，并主动参与治理。一个简单的追问——“从家到最近的地铁站有多远？”——就可能暴露规划盲区；一次对社区绿地的集体维护，可能孕育出新的归属感。当居民对“孩子能否安全步行上学”或“夜间能否在街头散步”提出要求时，城市治理便获得了源源不断的自下而上的动力。

当然，个体的努力无法替代系统性变革。可持续城市要求各级政府将SDG目标转化为本地法律、预算和长期规划，也要求私营部门在房地产、交通和能源领域拥抱绿色标准。但若没有无数公民的持续施压与协作，任何顶层设计都可能悬浮于现实之上。

城市未来：从负担到希望

城市转型的开支常常被视为负担，但联合国的分析显示，与收益相比，这一成本微不足道。投资于网络化的公共交通系统，不仅能够减少碳排放，还能大幅提升经济活力、公共健康和社会公平。一个运转良好的城市，应当让不同收入、年龄和背景的人都能共享密度带来的好处，而不是被密度所压迫。Cities occupy 3% of the Earth's land, yet host more than half of the population and determine three-quarters of global emission pathways. In other words, building sustainable cities is not about protecting cities, but about finding a structure that can sustain human civilization. The answer has long been written in the history of cities themselves: cities have never been static entities, but products that continually reshape themselves through governance and collective action. Faced with this century-defining challenge, what we need is not pessimism or fantasy, but the courage and imagination to reinvigorate urban governance.