Winter mortality in a warming climate: a reassessment

Abstract

In temperate climates, mortality is higher in the winter than the summer. Most wintertime deaths are attributed to cardiovascular and respiratory disease, with hypothermia from extreme cold accounting for a negligible share of all recorded deaths. International and national assessments of the health risks of climate change often conclude that increased temperatures from climate change will likely reduce winter mortality. This article examines the support for this hypothesis. We find that although there is a physiological basis for increased cardiovascular and respiratory disease mortality during winter months, the limited evidence suggests cardiovascular disease mortality is only weakly associated with temperature. Although respiratory disease mortality shows a stronger seasonal relationship with colder temperatures, cold alone does not explain infection rates. Further, respiratory disease mortality is a relatively small proportion of winter deaths. Therefore, assuming no changes in acclimatization and the degree to which temperature-related deaths are prevented, climate change may alter the balance of deaths between winters and summers, but is unlikely to dramatically reduce overall winter mortality rates.due to extreme temperature events that more deaths occur in temperate regions in the winter, generally defined as the three coldest months of the year, is well documented. 5,6 The question is how much of this seasonal variation is directly dependent on temperature versus other factors that vary with the seasons.This article explores the nature and evidence of the relationship between daily mortality, cold spells, and the cold season by first discussing the health impacts of cold temperatures and differentiating between mortality due to cold spells and general winter mortality. We then explore the evidence for the assumption that elevated winter mortality is due directly to temperature to draw conclusions regarding how the balance of hot-and cold-temperature-related mortality could be affected by a changing climate.

Climate change impacts on extreme temperature mortality in select metropolitan areas in the United States

“…By isolating the effect of single days of extreme cold temperatures the study results should not be affected by confounding factors related to generally higher wintertime mortality rates such as increased respiratory infections and cardiovascular disease (Medina-Ramon and Schwartz 2007;Mercer 2003). Several recent literature reviews suggest that the factors leading to these higher wintertime mortality rates are unlikely to be sensitive to climate warming (Ebi and Mills 2013;Kinney et al 2012), and therefore the changes in cold mortality identified by this study are likely to compose the majority of the changes in winter-time deaths resulting from warming.…”

Greater understanding is need of whether warmer and shorter winters associated with climate change could reduce winter mortality

“…A key question is whether these deaths are seasonal because of temperature (e.g. temperature is a proximal cause of these deaths, much as hot temperatures are a proximal cause of summer mortality) or whether deaths are seasonal for other reasons (Ebi and Mills 2013). Understanding this is important because climate change is projected to increase average ambient temperature in winter months and shorten the duration of the winter season (IPCC 2014).…”

Health and climate change: policy responses to protect public health

“…There is a stronger link between respiratory deaths and colder temperatures but these account for a smaller percentage of winter deaths. 46 The impact of cold temperatures can be measured considering seasonal means, extreme cold spells, and relative temperature changes. Seasonal means and extreme cold spells (or absolute temperature) have relatively small or ambiguous relationships with numbers of winter deaths, however temperature cooling relative to an area's average temperature does more clearly correlate with mortality rates.…”

“…Seasonal means and extreme cold spells (or absolute temperature) have relatively small or ambiguous relationships with numbers of winter deaths, however temperature cooling relative to an area's average temperature does more clearly correlate with mortality rates. 46,47 There may be modest reductions in cold-related deaths; however, these reductions will be largely outweighed at the global scale by heat-related mortality. 46 Whilst climate change will have an impact on cold-related deaths, particularly in some countries with milder climates, the overall impact is uncertain.…”

“…46,47 There may be modest reductions in cold-related deaths; however, these reductions will be largely outweighed at the global scale by heat-related mortality. 46 Whilst climate change will have an impact on cold-related deaths, particularly in some countries with milder climates, the overall impact is uncertain. 48,49 Population growth, urbanisation trends, and migration patterns mean that the numbers exposed to hot temperature extremes, in particular, will increase, with major implications for public health planning.…”