Climate crisis or public health threat? WMO connects increasing temperatures to a rise in dengue cases

Summary:
The World Meteorological Organization reports that 2015–2025 has been the hottest decade on record, with rising temperatures increasingly influencing the spread of diseases like dengue. Once confined to tropical regions, dengue is now expanding rapidly, with a record 14.4 million cases in 2024, driven by warmer climates, shifting rainfall patterns, and extreme weather that favour mosquito growth and virus transmission. Studies show even small temperature increases can significantly raise infection risk, while global spread has surged to over 130 countries, according to the World Health Organization. At the same time, prolonged heat exposure is creating a parallel health crisis, weakening immunity and affecting over a billion workers worldwide. The findings highlight how climate change is intensifying health risks, underscoring the urgent need for stronger public health systems, climate-aware policies, and improved disease prevention measures. 

The decade from 2015 to 2025 has been the warmest on record, according to the World Meteorological Organization’s State of the Global Climate 2025 report. This persistent increase in temperatures is no longer solely an environmental issue; it is increasingly shaping the way diseases develop and spread.

Dengue, once mostly limited to specific tropical zones, is now rapidly extending its reach. The report points out that rising heat is not only accelerating the spread of the disease but also worsening the severity of outbreaks. At the same time, changing climate patterns and more frequent extreme weather events are creating favourable conditions for transmission. Consequently, the health impacts of global warming are becoming more apparent and harder to overlook.

The worldwide surge in dengue cases underscores the strong link between the disease and climate conditions. In 2024, approximately 14.4 million cases were recorded—the highest number to date—and the infection is spreading into new regions and higher elevations where it was previously uncommon. Meanwhile, transmission periods are growing longer and more unpredictable, driven by increasing temperatures and shifting rainfall patterns, both of which are intensifying outbreaks.

A 2025 study published in the BMC Public Health journal found that a 1°C increase in temperature can raise the risk of dengue infection by 13 percent. The virus reproduces most efficiently between 32°C and 35°C, making hot environments particularly conducive to its spread. Warmer conditions also accelerate mosquito breeding and biting activity, while reducing the time required for the virus to develop within the mosquito.

Together, these factors mean that higher temperatures not only boost mosquito populations but also make each mosquito more effective at transmitting the virus, thereby increasing both the scale and intensity of outbreaks.

According to the World Health Organization (WHO), dengue has expanded significantly over the past five decades, growing from fewer than 10 endemic countries in the 1970s to more than 130 today. The greatest burden is observed in Latin America, Asia, and parts of Africa. Rapid urban growth, inadequate water and waste management, and increased human mobility have facilitated the spread of Aedes mosquitoes, while climate variability has enabled transmission to extend into some temperate regions.

• Higher rainfall and humidity create more stagnant water, encouraging mosquito breeding
• Warmer winters allow mosquitoes to survive in areas that were previously too cool
• Urban expansion and poor waste disposal generate micro-environments that support mosquito growth

As a result, over half of the world’s population now lives in areas at risk of dengue, and regions that once experienced occasional cases are now facing continuous outbreaks.

Chronic and extreme heat stress: A parallel crisis

The WMO report also highlights a broader health challenge associated with rising temperatures. Exposure to heat is steadily increasing, with some regions experiencing hundreds of additional hours of heat stress annually. Over time, this prolonged exposure leads to chronic heat stress, which can weaken the immune system and heighten susceptibility to infections.

This impact is particularly evident among workers. More than one-third of the global workforce—around 1.2 billion people—faces heat-related risks each year, especially in sectors such as agriculture and construction. Elevated temperatures contribute to fatigue, dehydration, injuries, and kidney strain, while also affecting mental well-being and reducing productivity and livelihoods.

Why this matters

The link between climate change and health is no longer abstract, and dengue stands out as a clear example of how rising temperatures translate into tangible disease risks.

• Heatwaves are becoming more frequent and severe, particularly in tropical regions
• Many healthcare systems are unprepared for outbreaks driven by climate factors
• Vulnerable groups, including children, older adults, and outdoor workers, face higher risks
• Climate-sensitive diseases are spreading faster than monitoring and response systems can keep pace

What needs to be done

Experts emphasize the importance of integrating heat-aware strategies into planning and policymaking, including stronger workplace protections to safeguard people from rising temperatures.

• Enhance early warning systems that connect weather data with disease surveillance
• Expand vector control efforts, particularly in high-risk areas
• Increase public awareness about preventing mosquito breeding
• Develop climate-resilient healthcare systems capable of addressing both heat stress and infectious diseases