By Daniel Brouse
July 20, 2025
Disease vectors are among the most critical--and often underestimated--risk factors of climate change. Together with deadly humid heat and increasingly violent rain events, these three threats drive an exponential rise in climate-related deaths. Disease vectors, such as mosquitoes and ticks, expand their range and transmission seasons as the climate warms, spreading infectious diseases to new regions and populations. Meanwhile, intensifying heatwaves push human bodies past their physiological limits, while extreme rainfall and flooding multiply health risks by spreading pathogens and destroying critical infrastructure. This deadly triad--disease, heat, and violent rain--underscores how climate change is not a distant threat but a present, accelerating driver of mortality worldwide.
My expertise on this topic follows a clear hierarchy: economics → risk management → climate change → pathogens.
These domains are deeply interconnected and critical to understanding the escalating risks shaping humanity's future:
Economics determines how societies allocate resources, influencing policy priorities, investment decisions, and the speed of response to emerging threats.
Risk management applies these economic frameworks to reduce vulnerabilities, design early interventions, and prevent crises before they escalate.
Climate change is a risk multiplier, destabilizing economies, displacing populations, and creating environmental conditions that increase the frequency and severity of disasters.
Pathogens are a direct and rapidly growing consequence of these compounding crises, as climate change accelerates the migration, mutation, and transmission of infectious diseases globally.
One of the most concerning consequences of climate change is the surge in pathogen risks driven by rising temperatures, shifting precipitation patterns, and increased human displacement. Climate hazards directly fuel the migration of disease vectors (such as mosquitoes and ticks), expand pathogen survival zones, and increase the frequency of spillover events into human populations.
A landmark Nature study underscored the urgency of this threat:
"Over half of known human pathogenic diseases can be aggravated by climate change."
Read the report (PDF)
Dr. Camilo Mora, lead author and associate professor at the University of Hawaii Manoa, explained:
"Climate hazards aggravated 58% of all known human pathogens. That is over half of infectious diseases discovered since the end of the Roman Empire."
These pathways include:
Warmer winters and longer warm seasons that allow vectors and pathogens to survive year-round.
Climate-driven displacement of people and wildlife that increases cross-species transmission risks.
Floods, droughts, and heatwaves that expand breeding grounds while weakening public health systems.
The report warns:
"The human pathogenic diseases and transmission pathways aggravated by climatic hazards are too numerous for comprehensive societal adaptations, highlighting the urgent need to work at the source of the problem: reducing greenhouse gas emissions."
As Dr. Mora noted:
"Managing one or two diseases is feasible. But when 58% of diseases are being affected or triggered in 1,000 different ways, it becomes clear we are not going to be able to adapt to climate change."
These risks are not theoretical--they are unfolding now:
COVID-19 remains a stark example of how environmental disruption, global movement, and inadequate preparedness can turn a pathogen into a global crisis.
Avian influenza (Bird Flu) has crossed into cows and subsequently to humans, resulting in deaths. Though sustained human-to-human transmission has not yet occurred, each spillover raises the risk.
Vibrio vulnificus (flesh-eating bacteria) infections are rising in warming coastal waters:
In 2025, four Floridians have died from Vibrio infections across multiple counties.
The bacteria enter the body through open wounds, causing necrotizing fasciitis, and can also be contracted from eating contaminated seafood.
About 1 in 5 infected people die, according to the CDC.
Dr. Antarpreet Jutla of the University of Florida warns that infections increase after hurricanes and in warmer waters, aligning with intensifying climate patterns.
The United States has experienced a record number of 1,000-year and 500-year floods this year across nearly every state, driven by a warming atmosphere's increased ability to hold and release moisture. These extreme floods act as potent disease multipliers by:
Contaminating water supplies with sewage, industrial pollutants, and animal waste, creating breeding grounds for bacteria, parasites, and viruses.
Displacing rodents and insects, increasing human exposure to vector-borne diseases like leptospirosis, West Nile virus, and other mosquito-borne illnesses.
Leaving behind standing water that accelerates mosquito breeding.
Promoting mold growth in homes, exacerbating respiratory illnesses.
As climate change drives more frequent and intense flooding, these cascading health hazards will further strain healthcare systems, demonstrating how climate-fueled floods escalate pathogen risks in real time.
Climate change is fueling the spread of Lyme disease and other tick-borne illnesses in Pennsylvania, which consistently reports some of the nation's highest Lyme disease case counts. Warmer winters and longer growing seasons are expanding the range and activity period of the blacklegged tick (Ixodes scapularis), allowing it to remain active later into fall and emerge earlier in spring. Increased humidity and shifting forest ecosystems support tick survival while altering the distribution of deer and rodent hosts necessary for their lifecycle.
These climate-driven shifts increase human exposure risk, leading to higher infection rates and adding strain to healthcare systems already burdened by climate-related health challenges. As warming accelerates, Lyme and other tick-borne diseases will continue to expand in range and intensity, underscoring the deeply interconnected risks between climate change and infectious disease dynamics.
Mosquitoes are far more than just a summertime nuisance -- the insects are the world's deadliest animal. Mosquitoes can spread disease when they bite, including West Nile Virus. In the first half of 2025, mosquitoes have tested positive for the virus in more than half of Pennsylvania's 67 counties, according to the Pennsylvania Department of Environmental Protection, which has categorized the current West Nile Virus risk in the state as "high." Warmer temperatures, wetter springs, and longer warm seasons allow mosquito populations to grow and persist, increasing the window for transmission and raising the risk of local outbreaks.
Beyond Lyme and West Nile, Pennsylvania is seeing climate-linked increases in other pathogens, including:
These examples illustrate how climate change is not a distant environmental issue but a current and escalating public health crisis in Pennsylvania. Warmer temperatures, shifting precipitation patterns, and ecological disruptions are amplifying the spread and severity of infectious diseases, increasing healthcare burdens while demanding urgent mitigation and adaptation strategies to protect public health.
Economics, risk management, climate change, and pathogens are not isolated challenges--they form an interconnected crisis that will shape our collective future.
Climate change is not just an environmental issue; it is a public health emergency, an economic destabilizer, and a risk multiplier. The rising threat of pathogens, compounded by climate disruption, proves that adaptation alone will be insufficient.
Reducing greenhouse gas emissions remains the only systemic intervention capable of mitigating these cascading risks while preserving the foundations of health, stability, and equity in human societies.
Disease vectors, violent rain, and deadly humid heat are driving an exponential rise in climate-related deaths. This lethal triad--infectious disease, extreme heat, and intense rainfall--demonstrates that climate change is not a distant concern but a present, accelerating force behind rising mortality worldwide. Together, these threats magnify each other's impacts, underscoring the urgent need to address climate change as a health crisis already unfolding.
* Our climate model -- which incorporates complex social-ecological feedback loops within a dynamic, non-linear system -- projects that global temperatures could rise by up to 9°C (16.2°F) within this century. This far exceeds earlier estimates of a 4°C rise over the next thousand years, signaling a dramatic acceleration of warming.
We analyze how human activities (such as deforestation, fossil fuel use, and land development) interact with ecological processes (including carbon cycling, water availability, and biodiversity loss) in ways that amplify one another. These interactions do not follow simple cause-and-effect patterns; instead, they create cascading, interconnected impacts that can rapidly accelerate system-wide change, sometimes abruptly. Understanding these dynamics is essential for assessing risks and designing effective climate adaptation and mitigation strategies.
Read: Solutions to the Fossil Fuel Economy and the Myths Accelerating Climate and Economic Collapse