For decades, cities have been designed around "gray infrastructure." Roads move people. Bridges connect communities. Water systems protect public health. These systems are governed by engineering standards because society recognizes that safety cannot depend on good intentions alone.Urban nature deserves the same recognition.In June, a heat wave gripped Europe, breaking temperature records across the continent. In France, officials reported over 2,000 excess deaths. In the U.K., hospitals declared critical incidents and machinery and IT systems failed. In the U.S., a heat dome over the Midwest and East Coast disrupted Fourth of July celebrations, with at least 25 heat-related deaths over Independence Day weekend. Cities are being tested by a warming climate. Yet one of our most effective forms of climate infrastructure is being lost not because it does not work but because we still do not treat it as infrastructure.My view is simple: Urban nature including street trees, parks, wetlands and other urban green spaces should be categorized and managed as essential infrastructure, with minimum standards for its protection, quality and long-term maintenance. Just as we regulate roads, bridges and drinking water, we need standards that ensure all urban residents benefit from healthy and thriving urban nature. Without such standards, cities will become hotter, less resilient and increasingly unequal as climate change accelerates.A cafe in the city of Nice during the heat wave that saw temperatures in France reach a record-breaking average of 98.4 degrees Fahrenheit (36.9 degrees Celsius). (Image credit: Valery Hache/Getty Images)Scientific research shows that urban trees and green spaces cool cities during heat waves, reduce flooding by absorbing stormwater, improve air quality, store carbon, support biodiversity, and improve both physical and mental health. During extreme heat, neighborhoods with mature tree canopies can be several degrees cooler than nearby streets dominated by concrete and asphalt. Those few degrees can mean the difference between manageable discomfort and dangerous heat exposure, particularly for older adults, children and people with existing health conditions.But while the science is strong, our governance is not.Cities enthusiastically announce ambitious tree-planting campaigns, biodiversity strategies and new greening targets. These initiatives are valuable, but they often focus on what is easy to count rather than what truly matters. Planting a tree is not the same as growing a healthy urban forest. Creating a park does not guarantee biodiversity. A green roof delivers little value if it fails during drought.The real measure of success is whether urban nature continues providing benefits decades after trees are planted and established.This is where cities are still falling short.That is not simply an environmental issue. It is a public health issue, a climate adaptation issue, and an issue of social equity.Unlike buildings or transport systems, urban nature rarely operates under consistent minimum standards. Many cities have no requirements for minimum tree canopy cover, adequate rooting space, soil quality, biodiversity targets, long-term maintenance or even whether newly planted trees survive. As a result, access to nature depends heavily on where people live. Wealthier neighborhoods often enjoy mature tree canopy and high-quality parks, while disadvantaged communities experience hotter streets, fewer green spaces and greater exposure to climate risks.That is not simply an environmental issue. It is a public health issue, a climate adaptation issue, and an issue of social equity.The solution is not simply to plant more trees. It is to establish urban nature standards that recognize nature as essential infrastructure.These standards would not prescribe the same solution for every city. Instead, they would establish minimum expectations based on scientific evidence. They could include targets for accessible green space, minimum tree canopy cover, sufficient soil volume for healthy tree growth, biodiversity outcomes, long-term maintenance funding and routine monitoring to ensure that urban nature continues delivering benefits to communities.The Bosco Verticale in Milan house around 800 trees and 20,000 plants. City officials have been expanding the green infrastructure with multiple high impact projects to address climate change. (Image credit: Emanuele Cremaschi/Getty Images)Importantly, these standards should focus on outcomes rather than simple planting targets. Counting how many trees are planted tells us little about whether cities are becoming more resilient. Measuring survival, canopy development, ecosystem health and equitable access provides a much better picture of whether investments in urban nature are actually returning dividends.Some critics argue that cities cannot afford stronger standards for urban nature. Municipal budgets are already stretched by housing, transport and aging infrastructure. But this argument overlooks a fundamental reality: We already spend enormous sums responding to the consequences of extreme heat, flooding, poor air quality and declining public health. Healthy urban ecosystems help reduce these costs while delivering multiple benefits simultaneously.RELATED STORIES'River in the Sky': China's doomed plan to create a 'cloud seeding corridor' tells us how far the country will go to solve its climate crisisDrinking wastewater, building an island from scratch and creating an urban forest: 3 bold ways cities are already adapting to climate changeWar has brought Iran's water crisis to a breaking point: 'Things will collapse unless there is meaningful structural change'As climate change accelerates, the distinction between gray and green infrastructure becomes increasingly blurred. Trees cool buildings and reduce energy demand. Wetlands decrease flood damage. Parks improve public health and strengthen communities. These are not optional amenities. They are functioning components of urban infrastructure that deserve the same level of planning, investment and accountability as any engineered system.Building codes transformed the safety of our cities because they established minimum standards that every development had to meet. Climate resilience now demands a similar transformation for urban nature.The next generation of resilient cities will not be defined simply by how many trees they plant but by the standards they adopt to protect, restore and sustain the living infrastructure urban life depends on.The real question is not whether cities can afford to invest in urban nature; it is whether they can afford not to.Opinion on Live Science gives you insight on the most important issues in science that affect you and the world around you today, written by experts and leading scientists in their field.