Mexico City Faces the Challenge of Planetary Boundaries

Lately, news of environmental deterioration in the great metropolis of Mexico City has been prominent. Not a single day goes by without mentioning environmental aspects or challenges: water shortages due to droughts, chaotic urbanization, poor air quality, increased allergies and respiratory diseases, illegal logging, deforestation in forested areas, to name a few.

Undoubtedly, the phenomenon of climate change plays a predominant role in this wave of heat, drought, and torrential rains that are already present and that we will increasingly witness. There is a consensus on the climate emergency and the need to find measures to mitigate its effects, to adapt and become resilient, and to face the destiny that has already reached us.

Although the fight against global warming is paramount, we cannot focus solely on it and fall into the trap of unilateral and biased remediation, as environmental deteriorations are multiple, as are their origins and consequences.

A few months ago, I addressed the scientific concept of planetary boundaries, which from a multidisciplinary perspective specify the safe conditions within which humanity can develop without causing irreparable damage to Earth’s system. They were first identified in 2009 by a group of scientists led by Johan Rockström and Will Steffen.

These boundaries encompass nine key aspects that regulate the stability and resilience of the planet, including climate change, biodiversity loss, ocean acidification, and deforestation. These boundaries are more relevant than if we focused exclusively on climate change because they offer a holistic view of the planet's health and all the interconnections of environmental issues. By considering multiple interconnected factors, planetary boundaries allow for a comprehensive approach to environmental challenges, ensuring that actions taken in one area do not compromise others, and promoting a sustainable and safe balance for life on Earth.

This comprehensive and cross-cutting methodology is relevant for shaping what should be the environmental policy of the future government of Mexico City since, due to the particularities, geographical, urban, and environmental characteristics of the megalopolis, Mexico City is a case study.

Let me explain. Mexico City is peculiar and stands out from other megacities on the planet because despite being among the Top 10 largest in the world, these are characterized by being exclusively large urban areas, such as Tokyo, New York, or the Paris region. In contrast, the territory of this great city is characterized by having more land of environmental value than urban land. Therefore, it needs to be visualized differently from the rest of the world's megalopolises.

However, it has to face the same challenges as any major city and carry out a gray environmental agenda to remedy its major ills: intense industrial activities, traffic congestion, urban planning, informal settlements, management of drinking and wastewater, and waste management and valorization.

But due to its geographical and ecological characteristics, by concentrating no less than 4% of the world's biodiversity and possessing 60% of its territory in conservation soil, which includes agricultural and environmental value soil, it has to simultaneously pursue a large green environmental agenda.

Thus, Mexico City needs to address the environmental problems of any urban area while also preserving and protecting agricultural and natural areas, and protecting endemic fauna and flora.

This is why the environmental policy of Mexico City must be completely comprehensive, cross-cutting, and inclusive, as it concentrates within it the vast majority of environmental challenges, a major complexity.

In this scenario, planetary boundaries and their methodology can become the axis to carry out the comprehensive policy that this city urgently requires. Environmental paradigms are closely interconnected. The degradation of one can increase that of another, and conversely, the improvement of one can benefit another, and in the face of the civilizational and socio-environmental crisis, it is no longer sustainable to work in a sectoral manner.

We must solve the problems of natural resource supply, goods, energy, transportation, public health, job creation, and others, while also avoiding changes in land use, adapting to climate change, protecting and restoring areas of environmental value, and conserving natural areas and all the region's fauna and flora.

Planetary boundaries allow us to focus on the essence of environmental challenges and their interconnections to take actions that truly impact remedying the crisis.

Planetary boundaries are scientifically delimited thresholds in biophysical processes that we must not surpass so that the biosphere can regulate, stabilize, and become resilient; for the case of Mexico City, these would be the following:

1. The limit of climate change:

This is mainly related to greenhouse gases (CO₂ and methane) in the atmosphere emitted by human activity. In the city, this is mainly due to vehicular transport, but it is also necessary to implement a policy to drastically reduce the volume of emissions from the city and its inhabitants because it affects global temperature, climate patterns, and ecosystems.

2. The limit of biodiversity erosion:

The world is experiencing the sixth mass extinction of species, equivalent to that of the Jurassic, when dinosaurs became extinct. By concentrating more than 4% of the world's biodiversity and as the habitat of numerous species of endemic fauna and flora, we must protect them because biodiversity is crucial for the resilience of ecosystems and the services they provide.

3. The limit of interruption of biogeochemical cycles:

Another problem we have is the interruption of nitrogen and phosphorus cycles in soils. There is sterilization not only in urban soils but also in conservation soils, and above all, in agricultural soils where biomass is spreading, affecting soil fertility, water quality, and aquatic ecosystems and ultimately maritime ecosystems.

4. The limit of land use change:

The expansion of urban sprawl and deforestation to feed growing populations causes habitat destruction and the conversion of natural land (forests, grasslands) into agricultural or urban land that affects biodiversity, soil quality, water and carbon cycles.

5. The limit on the global use of freshwater:

Water is synonymous with life, so it is essential to have sufficient quantities and qualities for the availability of all humans, but also of all living beings. It is essential for the survival of terrestrial and human ecosystems.

6. The limit of aerosol emissions into the atmosphere:

Human activities, especially industrial ones, but also motorized displacements, emit solid, volatile, and liquid particles suspended in the air that affect climate, air quality, and therefore human health.

7.  The limit of stratospheric ozone depletion:

Another important planetary boundary, where there is a record of improvement, has to do with the concentration of ozone in the stratosphere, which was destroyed by refrigerant gases and aerosols. But thanks to the studies of the Mexican Nobel laureate Mario Molina, the prohibition of these gases was achieved , thus protecting life on Earth from harmful UV rays.

8.  The limit of the introduction of new entities:

Finally, the boundary that is most relevant to Mexico City is the introduction of new entities related to the release of new substances into the environment (plastics, chemicals). The industry is moving at such a pace that new chemical and polymer substances are created daily without any control, potentially having a dangerous and unpredictable impact on health and ecosystems.

These boundaries are interconnected, and significant alteration of one can affect the others, compromising Earth's ability to maintain favorable conditions for human life. Therefore, the use of planetary boundaries to guide Mexico City's environmental public policies allows decisions to be based on precise scientific thresholds that mark safe ecological limits for the Mexico Valley. These boundaries identify critical environmental tipping points, such as climate change, biodiversity loss, and disruption of nitrogen and phosphorus cycles, beyond which ecosystems could suffer irreversible damage. By integrating these boundaries into policies, governments can adopt more specific preventive and corrective measures, thus ensuring the sustainable management of natural resources, the preservation of biodiversity, and the reduction of environmental disaster risks. This leads to more coherent and effective actions to protect the environment while simultaneously supporting economic and social development.