Climate Change Causes Heart Attacks? A Second Look at the Data

A slew of recent studies has suggested that climate change is increasing the number of heart attacks worldwide. This hypothesis suffers from many critical deficiencies, the most important being that rates of heart disease (and thus heart attacks) in the industrialized world have plummeted as our ability to prevent and treat coronary artery disease (CAD) has improved.

Studies that have reported a slowdown in this trend have also detected rises in the prevalence of obesity, metabolic syndrome, and type 2 diabetes—all well-known risk factors for heart disease. See my recent story Heart-Stopping Stupidity: Climate Change Isn't Increasing Heart Attacks for more data that doesn't fit the prevailing narrative about heart health and climate.

Here I want to examine some of the literature cited in support of the climate-heart attack hypothesis. As we go, you'll see that this research is highly speculative. Scientists, sometimes by their own admission, have drawn alarming conclusions from incomplete data sets and speculated that climate change might exacerbate existing risk factors for heart disease.

Unfortunately, these qualifications are usually buried deep in academic articles written for other experts, which means the public probably doesn't know about them. Consider this June 2022 analysis, Climate change and cardiovascular disease: implications for global health, published in Nature Reviews Cardiology. The paper's abstract warns readers in no uncertain terms that,

Climate change is the greatest existential challenge to planetary and human health … In this Review, we aim to provide an overview of the consequences of climate change on cardiovascular health, which result from direct exposure pathways, such as shifts in ambient temperature, air pollution, forest fires, desert (dust and sand) storms and extreme weather events.

I'd place poverty, which kills millions of children annually, above climate change if we're measuring threats to human and planetary health. [1] That aside, the argument is clear as day: climate change has consequences for cardiovascular health that stem from many exposure pathways. Now, let's look at the specifics from the same paper.

Messy epidemiological data

The authors began by addressing the existing literature on “The association between short-term environmental exposures related to climate change ... and cardiovascular outcomes.” This research, they noted, finds some correlation between variables like ambient temperature, particulate matter (PM), O₃ levels, and adverse heart health outcomes. This can represent a greater risk to people already vulnerable to heart attack, though extreme temperatures incentivize societies to develop infrastructure that makes inclement weather less dangerous. This is why living in modern-day Arizona is preferable to residing in Minnesota in 1500.

Those details aside momentarily, remember that heart disease develops over 10-plus years, not in a matter of weeks or months. Climatologists tend to study weather averages (precipitation, temperature, humidity etc.) over several decades. To say anything with confidence about the lasting impact of climate on heart health, we need long-term studies, and data of that sort tells a different story, the authors noted:

Health effects of long-term (such as yearly or seasonal) temperature patterns are far less studied than the health effects of short-term extreme weather events, and the available data on the effects of long-term exposure to elevated or reduced ambient temperatures on cardiovascular outcomes are sometimes inconsistent.

The footnote for this paragraph linked to a June 2021 systematic review of the association between total and cardiopulmonary mortality and morbidity and changes in ambient temperature. “Sometimes inconsistent” in no way summarizes its results.

The reviewers pointed out that “cold rather than hot temperature” is more strongly associated with cardiovascular mortality, which was a problem long before anyone cared about anthropogenic climate change. They reported “interesting associations” between long-term unusual temperature levels in specific areas and differences in health outcomes, “but the number of studies by design and health outcome was small.” More importantly,

Risk of bias was identified because of the use of crude exposure assessment and inadequate adjustment for confounding. More and better designed studies, including the investigation of effect modifiers, are needed.

In other words, this is not very good data. Scientists and reporters who alarm the public about the heart-harming effects of climate change are overstepping the evidence.

What about indirect effects?

The Nature authors then outlined a scenario in which climate change has many indirect effects on heart health. The idea is that various climatic changes brought on by CO2 emissions act as effect modifiers on variables scientists have already linked to cardiovascular health.

For example, many studies have posited that exposure to different pollutants increases the risk of heart attacks. Heat waves, which may increase in frequency with rising global temperatures, can increase ozone levels and particulate pollution in the atmosphere. As a result, climate change could indirectly increase heart attack rates.

There is a critical problem with this hypothesis, however. According to the EPA, the amount of pollution we produce in the US has declined markedly in recent decades:

The emissions reductions have led to dramatic improvements in the quality of the air that we breathe. Between 1990 and 2020, national concentrations of air pollutants improved 73 percent for carbon monoxide, 86 percent for lead (from 2010), 61 percent for annual nitrogen dioxide, 25 percent for ozone, 26 percent for 24-hour coarse particle concentrations, 41 percent for annual fine particles (from 2000), and 91 percent for sulfur dioxide.

Whatever effect climate change has on these pollutants has to be decreasing as we emit fewer of them, suggesting that the public health consequences are also declining. That appears to be the case. The EPA explains that “the Clean Air Act Amendments of 1990 are achieving large health benefits that will grow further over time ...” Among these health benefits, the agency lists a significant drop in acute myocardial infarction—“heart attack” in the vernacular.

A similar trend can be seen in other industrialized countries: as pollution has decreased, their populations have gotten healthier. Pollution is worse in poorer nations, though the same improvements can be seen as they grow wealthier and begin to invest in environmental protection. Crucially, though, heart disease rates in developing countries are primarily driven by the lifestyle factors that afflict us in the West—tobacco use, diabetes, dyslipidemia, high blood pressure, and obesity. Fearing the indirect influence of climate change while millions of people continue chain smoking and overeating is wasted anxiety.

Conclusion

Ultimately, I agree with the Nature authors' conclusion that “More work is needed to understand the adverse effects of environmental stressors on cardiovascular health.” They were also correct to suggest that “further insights gleaned from these investigations” should encourage us to mitigate the impact of climate on human health.

I would add two important exceptions to their summary. First, don't exaggerate the limited data we have while waiting for better evidence to come in, for that unnecessarily scares the public. Second, learn to accept good news when you hear it. We're getting better at reducing our environmental footprint and treating sick people. We can mitigate the adverse effects of weather under those conditions. That's a fact worth celebrating.

[1] Pollution is often worse in developing countries because they don't have the resources to fund environmental protection efforts. The same applies to pollution's health effects. They're worse in regions that lack access to high-quality health care.