I spent my clinical career in the most extreme corner of medicine, heart and lung transplantation. At least weekly I’d cut out a failing heart and replace it with a healthy heart from someone who died tragically. Transplant is the last resort, a radical act when everything else has failed. That experience convinces you of one thing: prevention matters most. If we can keep hearts healthy and thereby delay or avoid the day when a transplant must even be considered, we save lives, but also years of vitality.
Dr. Bill Frist, then-head of the Vanderbilt Multi-Organ Transplant Center, holding a diseased heart removed from a patient who would receive a healthy transplanted heart organ.
John Howser, Vanderbilt University Medical Center
That lens of a career treating heart disease colors how I see the changing climate, the increase in extreme weather patterns, the hotter days we are all experiencing. Climate change, thus to me, is not abstract. It is a direct, measurable, and increasingly dangerous threat to the heart. Mine and yours and those of your children and your grandchildren. And the science is now overwhelming.
According to the World Meteorological Organization, NOAA, and NASA, 2024 shattered climate records as the hottest year in history, becoming the first calendar year to exceed 1.5 °C above pre-industrial temperatures—a critical Paris Agreement threshold. The long-standing march of warming that began with the Industrial Revolution continues unabated, making 2024 not an anomaly, but the latest and most alarming marker in a century-and-a-half-long ascent. These are the facts.
Map of global average surface temperature in 2024 compared to the 1991-2020 average, with places that were warmer than average colored red, and places that were cooler than average colored blue. The planet’s 10 warmest years since 1850 have all occurred in the past decade. Based on data from NOAA’s National Centers for Environmental Information
NOAA Climate.gov, using NOAA NCEI data
Heat and the Heart
When the body faces extreme heat, it works hard to cool itself. It’s basic physiology one learns the first year in medical school: blood vessels dilate, heart rate climbs, and cardiac output rises.
And from there it’s supply and demand. All this substantially raises the heart’s demand for oxygen and this can tip vulnerable patients toward ischemia, irregular heartbeats (arrhythmias), or heart-failure decompensation.
A recent meta-analysis shows that every 1 °C temperature increase is associated with a 2% increase in cardiovascular (CVD) mortality, and during heat waves, cardiovascular deaths rise roughly 17%, with the largest effects in older adults. Dehydration, frequently occurring on hotter days, compounds risk by concentrating blood and promoting thrombosis, another path to heart attack (myocardial infarction) or stroke.
Heat matters to your health.
Coronary Artery Disease and Pollution
Climate change also worsens a proven driver of coronary disease: fine-particle air pollution (PM2.5) from combustion and, more frequently, from wildfire smoke and dust storms in a warmer, drier world.
Long-term PM2.5 exposure causally increases ischemic heart disease and cardiovascular mortality, even at concentrations below current standards, via a well documented combination of oxidative stress, endothelial dysfunction, autonomic imbalance, and thrombosis. A landmark longitudinal study from the Multi-Ethnic Study of Atherosclerosis and Air Pollution (MESA Air) cohort showed that higher exposures to PM2.5 and traffic pollution accelerate progression of coronary artery calcium, an objective indicator of atherosclerosis (or “hardening of the arteries”) which is the substrate of most heart attacks.
For those interested in the data: A meta-analysis of 35 studies found that every small rise in air pollution (an extra 10 μg/m³ of PM2.5 particles in the air), the risk of being hospitalized or dying from heart failure went up by about 2%.
Why does climate change make pollution worse? Hotter, sunnier, stagnant days boost ground-level ozone; warming increases the frequency and intensity of wildfires; and more atmospheric stagnation events trap pollutants near where people live. Together, these dynamics elevate exposures that cause direct damage to your heart and your cardiovascular system.
Arrhythmias and Heart Failure
Everyone knows someone with irregular heart beats, maybe atrial fibrillation (AF) or premature ventricular contractions. As we age the risk of AF increases (I have had an atrial ablation for symptomatic fib-flutter). Arrhythmias are common but they are made worse by the changing climate. The heart’s electrical system is heat- and pollution-sensitive. A multi-city analysis of patients with implanted cardiac devices found a dose-response link between extreme outdoor heat and atrial tachyarrhythmias/atrial fibrillation, or as the study summarizes: “Extreme hot outdoor temperatures were significantly associated with higher odds of AF episodes” among this patient population. Short-term PM2.5 surges also correlate with spikes in arrhythmias and heart-failure exacerbations through autonomic and ischemic mechanisms.
What We See in Emergency Rooms
As a thoracic surgeon at Stanford and Vanderbilt, I’d rotate through coverage in the emergency departments. My former colleagues remind me that their emergency departments have documented sharp increases in heat-related illness visits during recent heat seasons. While “heat-related illness” codes are broader than strictly cardiac, the physiologic pathways I mention above explain why cardiovascular events climb during heat waves—especially in older adults and those with existing heart disease.
Heat stoke prevention recommendations and symptoms to watch for on hot days.
getty
Inflammation: A Common Pathway
One unifying thread that has emerged over the past decade or so is inflammation. High-sensitivity C-reactive protein (hsCRP) is a marker of systemic inflammation (driven by IL-1β → IL-6 → CRP) that tracks future cardiovascular risk, even though CRP itself is not the causal actor. Your primary care physician likely tracks yours, especially as you age.
This maybe more than you want to know but the randomized CANTOS trial (the Canakinumab Anti-inflammatory Thrombosis Outcomes Study) tested this biology: blocking IL-1β reduced major cardiovascular events without lowering lipids, and benefits were greatest in those achieving lower on-treatment hsCRP, which is strong evidence that inflammatory pathways are causal in atherosclerosis. In short, this shows that inflammation itself plays a key role in clogged arteries – and targeting inflammation is important for successful treatment and prevention. And that is why hsCRP is so important to follow as a marker and measure of risk of disease.
This is one reason the Green Heart Louisville project (initially funded in part by The Nature Conservancy and conducted in association with the National Institutes of Health) is so compelling. It is a cluster-randomized, community-level greening trial designed to test whether adding thousands of trees and shrubs to neighborhoods can improve cardiometabolic health by lowering heat, pollution, noise, and stress. Emerging interim results show 13–20% lower hsCRP among residents in “greened” areas versus controls, consistent with reduced systemic inflammation, pending final peer-reviewed outcomes. Such nature-based solutions markedly reduce heat, and powerfully pull carbon and damaging pollutants out of the air.
The Scientific Verdict
The evidence is decisive. The pathophysiology is well understood. The conclusions are clear. Hotter days strain the heart and raise cardiovascular deaths, air pollution (including climate-amplified smoke and ozone) causes coronary artery disease and triggers arrhythmias and heart failure, and inflammation is a shared pathway that leads to disease, one we can measure and actively modify.
So that brings me back full circle. As a heart transplant surgeon at Vanderbilt, I treated patients at the very edge of survivability. But as a scientist and former policymaker, I cannot ignore what the data say: climate change itself is a cardiovascular risk factor. It is one that touches your family, your neighborhood, and every heartbeat. So, we must care and maybe even act.
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