Climate Change and Human Health Security: Rising Threats to Global Wellbeing

Climate change is no longer a distant threat-it is actively reshaping the health landscape for billions of people worldwide. From the air we breathe to the water we drink, rising temperatures and extreme weather events are creating new health challenges while amplifying existing ones. The World Health Organization considers climate change the single biggest health threat facing humanity, with projections suggesting an additional 250,000 deaths annually by the 2030s from climate-related causes alone. Understanding how our changing climate affects human health security is essential for protecting communities now and in the future.

How climate shapes human health
Waterborne diseases and flooding
The cholera connection
Beyond cholera: the broader picture
Vector-borne disease transmission
Malaria on the move
Dengue’s dramatic expansion
The warming advantage for vectors
Vulnerability of low-income populations
The geography of injustice
Limited adaptive capacity
Compounding health inequities
Building climate-resilient health security

How climate shapes human health

Human health has always been influenced by local weather conditions and regional climate patterns. Climate change affects human health both directly-through extreme weather events like heatwaves, storms, and floods-and indirectly through impacts on air quality, water supplies, food systems, and the spread of infectious diseases. These environmental shifts are degrading the fundamental ingredients of good health: clean air, safe drinking water, nutritious food, and secure shelter.

The World Economic Forum estimates that by 2050, climate change could cause an additional 14.5 million deaths and $12.5 trillion in economic losses worldwide. Healthcare systems will face an extra $1.1 trillion burden from climate-induced health impacts, creating significant strain on already stretched medical resources and personnel.

Recent research has begun quantifying these impacts more precisely. Scientists now attribute 37% of heat-related deaths to human-induced climate change, and heat-related mortality among adults over 65 has risen by 70% in just two decades. Meanwhile, food insecurity is worsening-in 2020, 98 million more people experienced food insecurity compared to the 1981-2010 average.

Waterborne diseases and flooding

Flooding events are increasing in frequency and intensity due to climate change, bringing with them a surge in waterborne illnesses. Heavy rainfall and floods can overwhelm water treatment systems, contaminate drinking water supplies with sewage, and create ideal conditions for pathogenic bacteria to thrive. The consequences are particularly severe in regions with limited sanitation infrastructure.

The cholera connection

Vibrio cholerae, the bacterium responsible for cholera, is highly sensitive to environmental conditions. Warmer water temperatures accelerate bacterial growth, while flooding events spread contamination across wider areas. Recent outbreaks demonstrate this connection clearly: seasonal rains in Myanmar during 2024 triggered a major cholera outbreak affecting 7,000 people, with deaths resulting from contaminated water sources.

South Asia faces particularly acute risks from this climate-health connection. Cholera outbreaks have occurred in Pakistan, India, and Bangladesh following major floods, alongside increases in typhoid, rotavirus, hepatitis A, and leptospirosis. Children defecating in public areas near water sources during monsoon seasons creates additional transmission pathways, as floodwaters carry pathogens into drinking water supplies.

Beyond cholera: the broader picture

Diarrheal diseases collectively represent one of the most climate-sensitive health outcomes. Systematic reviews of epidemiological literature have found consistent positive associations between flooding events and increased diarrheal disease rates. Studies report higher diarrhea rates during flood periods compared to pre-flood periods, with some research demonstrating exposure-response relationships where greater contact with floodwaters correlates with increased illness risk.

Drought, while seemingly the opposite of flooding, also increases waterborne disease risks. When water becomes scarce, people may resort to drinking from contaminated sources. Reduced water availability also means less handwashing and poorer hygiene practices, facilitating disease spread. The dual threats of too much and too little water both converge on the same outcome: more people falling ill from preventable waterborne infections.

Vector-borne disease transmission

Temperature, rainfall, and humidity fundamentally determine where disease-carrying insects can survive and reproduce. As climate patterns shift, vectors like mosquitoes and ticks are expanding into previously unsuitable territories, bringing diseases like malaria, dengue, and Lyme disease to new populations.

Malaria on the move

Vector-borne diseases account for more than 17% of all infectious diseases and cause over 700,000 deaths annually. Malaria, transmitted by Anopheles mosquitoes, remains one of the deadliest. The geographic range of these mosquitoes is shifting with climate-from 1898 to 2016, Anopheles mosquitoes gained an average of 6.5 meters of elevation per year and moved poleward by 4.7 kilometers annually. Higher altitudes and latitudes that were once too cold for malaria transmission are becoming suitable habitat.

In highland regions of Africa and Asia, warmer temperatures at higher elevations are creating new transmission zones. Models based on malaria case data from Colombia and Ethiopia suggest northward and upward spread along elevational gradients, with communities at higher altitudes experiencing more cases during warmer climate years.

Dengue’s dramatic expansion

Dengue is the most rapidly spreading mosquito-borne disease, with a 30-fold increase in global incidence over the past 50 years. Transmitted by Aedes mosquitoes, which thrive in urban environments, dengue now affects over 100 countries with an estimated 100-390 million infections yearly. In October 2023 alone, more than 4.2 million dengue cases were reported globally-compared to just half a million in 2000.

Climate change is expanding suitable habitat for dengue vectors into temperate regions. According to research published in The Lancet Planetary Health, an additional 4.7 billion people may face risk from malaria and dengue by 2070. Previously confined to tropical regions, travelers in southern Europe now report contracting dengue locally, signaling the disease’s expansion beyond its traditional boundaries.

The warming advantage for vectors

Warmer temperatures benefit disease vectors in multiple ways. Research from Stanford University shows that higher temperatures increase disease transmission up to an optimum point by accelerating mosquito development, shortening the time between blood meals, and speeding up pathogen development within the vector. For malaria parasites specifically, elevated temperatures increase the parasite development rate within mosquitoes, enhancing their ability to infect human hosts.

Extended warm seasons also mean longer active periods for disease-carrying insects. Mosquitoes that once died with the first frost are surviving longer, and mosquito seasons are expected to extend by one to two months by 2050 for species that transmit dengue, Zika, yellow fever, and chikungunya. Similarly, ticks remain active longer in milder winters, increasing opportunities for transmitting Lyme disease and other tick-borne infections.

Vulnerability of low-income populations

Climate change is not an equal-opportunity threat. The people whose health is being harmed first and worst are those who contribute least to the problem and have the fewest resources to protect themselves. This creates a profound climate justice issue where vulnerability and responsibility are inversely related.

The geography of injustice

The World Bank reports that the 74 lowest-income countries produce only one-tenth of global greenhouse gas emissions, yet they face the most severe climate impacts. In vulnerable regions, the death rate from extreme weather events in the last decade was 15 times higher than in less vulnerable areas. The richest countries, representing just 16% of the world’s population, produce nearly 40% of carbon dioxide emissions, while the two poorest country categories-comprising almost 60% of global population-generate less than 15%.

Extreme weather events are deeply intertwined with these global patterns of inequality. The poorest and most vulnerable people bear the brunt of climate impacts through job losses, physical harm, disease, mental health effects, food insecurity, water stress, and forced displacement. By 2050, projections suggest 216 million people will be displaced as climate refugees, with the largest numbers in sub-Saharan Africa, East Asia and the Pacific, and South Asia.

Limited adaptive capacity

People with low economic status lack access to the adaptive technologies and healthcare resources that could buffer them from climate impacts. According to the U.S. Environmental Protection Agency, socially vulnerable groups face greater climate-related health risks because they often live in locations prone to flooding, extreme heat, and air pollution; have higher rates of pre-existing medical conditions that climate impacts worsen; reside in areas with poorly maintained infrastructure; and face financial, cultural, or language barriers to accessing healthcare and social services.

Low-income households are more likely to have high energy burdens-a recent study found 25% could not afford to pay an energy bill in the past year. This means they may lack air conditioning during dangerous heat waves or struggle to maintain safe indoor temperatures. In the United States, 70% of the most hazardous waste sites are located within one mile of federally assisted housing developments, placing low-income residents at heightened exposure to toxic runoff during flooding events.

Compounding health inequities

Climate change does not create health disparities-it amplifies existing ones. Communities that already face structural disadvantages experience disproportionate impacts from extreme heat, flooding, and infectious disease expansion. Children in low-income families face compounded risks: their developing bodies are more vulnerable to environmental stressors, while their families have fewer resources to mitigate exposures or access medical care when illness occurs.

The global health impacts translate into staggering human costs. By 2030, an additional 48,000 children under age 15 are predicted to die from climate-related diarrheal illness. Meanwhile, heat stress is projected to reduce global working hours by 2.2% and cost the global economy $2.4 trillion annually, with outdoor workers in developing nations bearing the heaviest burden.

Building climate-resilient health security

Protecting human health from climate change requires action on multiple fronts. The World Health Organization emphasizes three key objectives: promoting actions that reduce emissions while improving health; building more climate-resilient healthcare systems; and protecting health from the wide range of climate impacts already underway.

Effective adaptation strategies include enhanced disease surveillance and early warning systems, climate-proofing water treatment infrastructure, strengthening vector control programs, and ensuring healthcare facilities can function during extreme weather events. Equally important is addressing the root causes of vulnerability through investments in education, poverty reduction, and universal healthcare access.

The path forward requires recognizing that climate action is health action. Every fraction of a degree of warming avoided represents lives saved and illness prevented. Communities that invest now in climate-resilient health systems will be better positioned to protect their most vulnerable members as impacts intensify in coming decades.

What do you think? How is climate change affecting health in your community, and what adaptations do you believe are most urgently needed to protect vulnerable populations?

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Table of Contents

How climate shapes human health 🔗

Waterborne diseases and flooding 🔗

The cholera connection 🔗

Beyond cholera: the broader picture 🔗

Vector-borne disease transmission 🔗

Malaria on the move 🔗

Dengue’s dramatic expansion 🔗

The warming advantage for vectors 🔗

Vulnerability of low-income populations 🔗

The geography of injustice 🔗

Limited adaptive capacity 🔗

Compounding health inequities 🔗

Building climate-resilient health security 🔗