Public Health Consequences of Global Climate Change: A Narrative Review

Climate change rarely appears on a medical chart as a single diagnosis. It arrives as heat exhaustion in an older person whose flat never cooled overnight. It appears in the lungs of a child breathing smoke from a distant wildfire, or in an infection carried by an insect now able to survive through a warmer season. The immediate illness has a familiar name. The climate has altered the conditions that made the illness more likely, more severe or harder for a health service to manage.

Anna Apetrei-Pandrea and I wrote this narrative review to bring those routes into one account. She led the two-author paper, and I contributed as second author. We searched recent peer-reviewed literature across major academic databases, giving priority to original studies and reviews published from 2010 onward while drawing on older work where the history or concept required it. A narrative review synthesises a broad field and explains how findings connect. It can reveal a pattern across disciplines, although it does not calculate one pooled effect in the way a formal meta-analysis might.

The pattern begins with a planet retaining more heat. Human activity has increased the concentration of greenhouse gases, which slow the escape of energy from the atmosphere. A rise in the global average can sound modest because nobody lives inside an average. Bodies experience the change through the frequency and duration of extreme heat, the warmer night that prevents recovery and the local combination of humidity or urban concrete that makes a given temperature dangerous.

Heat strains the body as it tries to keep its internal temperature within a narrow range. Sweating and increased blood flow to the skin help release warmth, yet both place demands on circulation and fluid balance. Older adults may regulate temperature less efficiently, while heart or kidney disease narrows the body's margin for adaptation. Certain medicines affect sweating or hydration. Outdoor workers face prolonged exposure and may have little control over their schedule. The same forecast therefore describes very different levels of risk.

Cities can intensify that difference. Dark surfaces absorb energy during the day and release it slowly after sunset, creating an urban heat-island effect. A tree-lined neighbourhood with well-insulated homes can cool sooner than an area dominated by traffic and concrete. Air conditioning offers protection, provided people can afford the electricity and the grid survives peak demand. Heat policy becomes housing and labour policy at this point. An alert helps only when the person receiving it has somewhere safer to go.

The air changes along with the temperature. Heat can increase ground-level ozone, an irritant that worsens respiratory disease. Longer dry periods and severe fires send fine particles across regions, sometimes far from the flames. These particles can penetrate deep into the lungs and enter the circulation. People with asthma or cardiovascular illness may deteriorate, and clinics can see a rise in demand while the same fire disrupts transport. One environmental event moves through several parts of the health system at once.

Infectious disease follows a less direct route. Mosquitoes, ticks and other vectors depend on temperature and moisture for survival. A warmer season may allow them to remain active longer or establish populations in places that were previously unsuitable. The pathogen must still be present, and human travel or local control can alter what happens next. Climate suitability creates an opportunity rather than a guaranteed outbreak. Surveillance needs to detect when that ecological possibility becomes transmission.

Water and food systems carry further consequences. Heavy rainfall can overwhelm sanitation, while drought concentrates pressure on scarce water and reduces crop yields. Warmer water may favour some harmful microbes. Food insecurity changes nutrition and can force families into difficult choices about work or migration. These pathways develop across months and institutions, making the climate contribution less visible than a heatwave. Their health effects can last longer because they reshape the conditions in which children grow and communities remain stable.

Mental health belongs inside this picture. A flood can bring acute trauma and the loss of a home. Repeated drought can erode a farmer's livelihood slowly, creating uncertainty that settles into daily life. People may grieve for a damaged place while fearing the next event. Services often arrive after a disaster and withdraw before the longer psychological consequences have become clear. Preparedness has to include continuity of care, especially for people whose previous treatment or social support has been disrupted.

Every pathway is filtered through inequality. Communities that contributed least to greenhouse-gas emissions may face the greatest exposure and have the fewest resources for protection. Within one city, income and housing can determine whether a hot night is uncomfortable or dangerous. Occupational rules affect whether a worker can stop. Access to primary care influences whether early symptoms receive attention. Climate change magnifies existing health differences because it acts through systems that were unequal already.

Age and biology create further differences within the same household. Pregnancy places additional demands on circulation and temperature regulation, while severe heat has been associated with adverse birth outcomes. Children breathe more air for their body size and depend on adults to change their environment. Older people may live alone or take medicines that affect hydration. A public-health plan becomes more useful when it identifies these pathways in advance and connects each warning with the people responsible for care.

Changing ecosystems can influence the movement of pathogens between animals and people as well. Habitat disruption alters which species meet, while changing temperature affects where hosts and vectors can persist. An unusual animal infection does not automatically become a human epidemic; several biological barriers still have to be crossed. The shifting pattern increases the value of surveillance that connects veterinary and human health. Signals in wildlife or livestock may offer an earlier view of a threat that will later concern clinicians.

Health services face their own exposure. Hospitals need cooling and electricity during heatwaves, clean water after floods and supply chains that continue when roads fail. A surge in respiratory illness can coincide with staff displacement or damaged facilities. Resilience therefore extends beyond an emergency plan stored in an office. Services can assess the risks around each building, protect essential power and maintain routes for medicines. Local knowledge matters because the same climate hazard reaches a coastal clinic and an inland hospital differently.

Adaptation reduces harm under the conditions already developing. Heat-health plans can connect forecasts with outreach to isolated residents and safer working hours. Vector surveillance can look for changes at the edge of a species' established range. Public communication can explain smoke exposure and where cleaner indoor air is available. These measures work when alerts lead to a practical action. A warning delivered without transport, shelter or employment protection transfers responsibility to the person with the fewest options.

Monitoring can show whether that action reaches the intended people. Health departments can compare emergency admissions during hot periods, map exposure alongside housing and examine who uses cooling centres. A successful programme may reduce illness even as temperatures continue to rise, so evaluation needs a credible baseline and attention to local change. The findings should return to neighbourhood organisations and clinical teams. Adaptation improves when the people experiencing the hazard can correct what the plan assumed about them.

Mitigation addresses the source by reducing greenhouse-gas emissions, and many measures bring nearer health benefits. Cleaner transport can reduce air pollution while making walking safer. Buildings designed for efficiency can stay more comfortable during extremes. Diet and land-use changes require careful local planning, since a policy that improves one measure can burden a community elsewhere. Health evidence helps compare these choices in terms people experience within a lifetime, alongside the longer planetary effect.

The review also confronts the gap between scientific evidence and public argument. Climate research contains uncertainty about the precise local size or timing of an effect, as every complex science does. That uncertainty has sometimes been misrepresented as evidence that the underlying process is doubtful. Clear communication distinguishes the robust finding from the range around a projection. It can say what is known, what remains conditional and which action is sensible across several possible futures.

Climate change is often described as an environmental issue with health added as one consequence. The evidence points toward a closer relationship. Climate shapes the air entering the lungs, the organisms capable of carrying infection and the stability of the systems that support daily life. Public health gives those connections a human scale. It also gives action a practical purpose: fewer people becoming ill in the heat, cleaner air this year and health services able to protect communities through the conditions already arriving.