by Daniel Brouse

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.

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.”

Pennsylvania Examples: Lyme Disease, West Nile Virus, and Emerging Pathogens

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:

• Babesiosis: A tick-borne parasitic infection increasingly detected in Pennsylvania, historically confined to New England, now spreading as ticks expand their range in warming conditions.
• Powassan Virus: A rare but severe tick-borne illness showing increasing cases in the Northeast, including Pennsylvania, driven by warmer winters allowing tick populations to survive and spread.
• Eastern Equine Encephalitis (EEE): Another mosquito-borne disease that can cause severe neurological symptoms and has seen increased activity in the region as warmer, wetter conditions improve mosquito breeding environments.
• Flesh-eating Vibrio bacteria: While primarily coastal, warming waters and increased flooding can spread Vibrio vulnificus inland through waterways, posing emerging risks as climate conditions shift.

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.

Conclusion: Interconnected Crises Require Urgent Action

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.

What you can do today. How to save the planet.

Read: Solutions to the Fossil Fuel Economy and the Myths Accelerating Climate and Economic Collapse

Tipping points and feedback loops drive the acceleration of climate change. When one tipping point is breached and triggers others, the cascading collapse is known as the Domino Effect.