Is Climate Change the Most Important Public Health Challenge of the 21st Century?
Recent climate-related events in the United States and worldwide, such as widespread floods, droughts, and wildfires, seem to indicate that climate change may be the most important public health challenge of this century.
Based on morbidity and mortality data alone, one could argue that the COVID-19 pandemic has been the more important challenge. But the question I have posed in this headline — and used to title Chapter 14 in the 7th edition of Schneider's Introduction to Public Health (2025, Jones and Bartlett) — should prompt re-evaluation of that argument.
No matter the answer to the question, the frequency and intensity of climate-related events have had enormous public health impacts at the local, regional, national and international levels. As the concentration of greenhouse gases increase, so does the frequency of such events all over the world.
The Earth’s temperature is increasing, seasonal rain and temperature patterns are changing, and the oceans are getting warmer. As result of these and many other climate-related changes, populations have been displaced, vector-borne diseases are expanding, and agricultural production has been affected.
The Effects of Climate Change Are Unequal
The Sixth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) determined that global greenhouse gas emissions continue to increase. These emissions have “unequal historical and ongoing contributions arising from unsustainable energy use, land use and land-use change, lifestyles and patterns of consumption and production across regions, between and within countries, and among individuals,” the IPCC concluded.
Over the last decades, millions of people have come to realize that they live in a new normal in which longer and hotter summers, warmer or colder winters, and wetter or dryer seasons have become the norm, depending on where you live on the planet. In sum, climate drivers are causing significant changes to what was considered normal in past decades.
In addition, our animal and plant planet cohabitants are suffering the negative impacts of climate change, highlighting the fact that we all live on one planet and therefore should view health as “One Health.”
It’s important to emphasize that not all populations suffer the adverse impacts of climate change on public health equally.
- Black and African-American people are 40% more likely than non-Black and non-African American people to live in areas with the highest projected increases in mortality rates due to climate-driven changes in temperatures.
- Hispanic and Latino people are 43% more likely than non-Hispanic and non-Latino people to live in areas with the highest projected labor hour losses in weather-exposed industries due to climate-driven increases in high-temperature days.
- Those experiencing greater climate change-associated health risks include children and older adults beyond low-income communities and some communities of color.
Addressing the Challenges of Climate Change Requires Focused Efforts
Governments and societies have developed mitigation and adaptation strategies and programs to reduce the impacts of climate change. Yet despite progress in the United States over the last few decades, overall responses by the public and private sectors are insufficient to address the enormous challenges. Why? Because there is no model for effective adaptation.
Policies established by government entities tend to be inconsistent with each other, because the perceptions of climate risks vary. Policy priorities may be influenced by resource availability and institutional competence and capacity. Other contributing factors are tensions between local and federal adaptation projects, and electoral incentives that favor visible over not-so-visible adaptations.
Despite the magnitude of climate-related events, the acceptance of climate change as a reality is still a matter of controversy in the United States and worldwide. A significant majority of scientists think that sufficient evidence supports climate change as an event resulting from mostly anthropogenic causes. But many organizations, politicians, individuals, and some scientists — the so-called climate deniers — classify climate change as a hoax, an exaggeration, a conspiracy against freedom, and an unacceptable government regulation of markets.
The Public Health Consensus Recognizes Impacts on all Living Beings
Fortunately, there is a growing consensus among public health professionals that climate change has become one of the most — if not the most — important public health crisis in the 21st century. This is based on its enormous impact on all living beings on planet Earth. Now more than ever, scientific evidence shows that the survival of numerous species, including humans, is at stake if countries do not reduce carbon dioxide emissions in the next decades.
Even though the relationships between public health and climate change have become clearer, responding to this threat is a work in progress. The complexity of the problem requires new data and many more studies to elicit statistical associations and causality.
On the other hand, we can’t wait for all the answers before taking action. Fundamental changes in the way people live, work and play are needed to direct our planet toward a sustainable future that promotes health equity and climate justice.
The solutions to climate crisis must include people from all walks of life. Only then can we build long-term social resilience and an ecologically just and equitable world.
Carlos Eduardo Siqueira is a Professor Emeritus at the University of Massachusetts School for the Environment, where he taught in the Department of Urban Planning and Community Development. He also served as coordinator of the Transnational Brazilian Project at the Mauricio Gastón Institute of Latino Community Development and Public Policy. Over his career, Siqueira has researched the political economy associated with the migration of hazards between developed and developing countries, immigrant health, health policy, and health and safety inequities in the workplace.