April 16, 2012
The potential for climate change to drastically alter the weather is by no means a new topic. We often hear of the potential for the formation of more severe hurricanes, widespread drought in some areas and widespread flooding in others. However, one type of event which often serves as a footnote to this discussion is the potential for climate change to drastically increase the incidence and severity of extreme heat events (EVEs), more commonly known as heat waves. Already, heat waves account for more deaths in the United States than any other weather phenomena. In fact, heat waves account for more deaths annually than hurricanes, tornadoes, floods and earthquakes combined (CDC). Despite this fact, heat waves are commonly overlooked as a major threat to a population – they kill silently and leave little or no physical destruction in their wake, leaving few lasting reminders of the danger that exist (Luper et al, 2008). Aside from the impact in human lives, extreme heat events put severe stress on healthcare services and energy supply and distribution networks, which can, in severe cases, result in major social and economic problems. With experts predicting more intense and frequent heat waves in the future, increased awareness and preparation will be crucial to mitigating the dangers associated with these extreme heat events.
While the nature of conditions which characterize a heat waves differs between organizations, the World Meteorological Organization recommends as a definition a situation where the daily maximum temperature of more than five consecutive days exceeds the average temperature by 5oC (9oF). Of particular note in this definition is the reference to five consecutive days of high temperature. This temporal element is what separates a heat wave from a situation when you may have one or two days of extremely hot weather – and this extended period of heat exposure is also what makes heat waves so dangerous.
Although local conditions (i.e. warm winds like the Santa Ana winds) can cause localized heat events and even regional heat waves, large scale heat waves like the one which struck Europe in 2003, killing over 70,000 people (wiki), are caused by a specific situation. The majority of heat waves occur when a high pressure air mass remains over a region for several days or even months. This high pressure sinks, warming as it does so, and also acts essentially as a ‘cap’ – trapping heat and stagnant air close to the ground and preventing warm air from rising (National Weather Service). The high pressure zone also limits convection, preventing convective clouds from forming and minimizing the chances for rainfall. This effect is particularly noticeable in cities, which are often significantly warmer than the surrounding area due to the urban heat island effect (largely caused by widespread use of heat-retaining materials). The extra heat generated by cities exacerbates the build-up of heat due to the atmospheric conditions, and can result in extremely high sustained temperatures and significant risk to the population (Luber et al. 2008).
From a physiological standpoint, heat waves and related sustained heat exposure can have a variety of effects, ranging in severity. Heat cramps, fainting, dizziness and heat exhaustion are common in heat wave scenarios and if steps are not taken to mitigate these effects, they can progress to nausea, cardiovascular problems and ultimately hyperthermia, also known as heat stroke (Luber et al. 2008). Heat stroke is an extremely dangerous condition which occurs when core body temperature reaches or exceeds 40.6oC (105oF). In this condition, the body looses the ability to regulate its temperature and severe central nervous system problems such as delirium, convulsions and coma may occur, and if steps are not made to immediately cool the victim, death will result. Naturally, individuals who have compromised ability to regulate body temperature due to old age, chronic diseases, or use of certain medications as well as individuals with cardiovascular problems are at extreme risk during these extreme heat events (Luber et al. 2008).
While heat waves themselves and the aforementioned risks are not new phenomena, there is a consensus in the scientific community that the temperature shift caused by climate change will result in much more frequent extreme temperature events, and also much more intense events (CDC, Luber et al. 2008, Huang et al. 2011). Using Los Angeles as an example, Hayhoe et al. (2004) predicts that heat waves and other extreme events will occur with a frequency four times greater than the current level (roughly 12 days annually) by 2100 using the more conservative B1 emissions scenario, and with a frequency up to 8 times greater than the current level using the more pessimistic A1fi emissions scenario. These predictions are consistent with predictions of increase extreme heat events and related mortality in other regions of the United States and the world. For example, Huang et al. (2011) predicts an increase of heat-related fatalities to increase from the current rate of roughly 700 people annually by 70-100% by the middle of the century, while Takahashi eta l. predicts that globally, deaths due to heat exposure may increase anywhere from 100-1000% of the current rate by the end of this century. Clearly, warmer, more frequent heat waves will have significant impact on human lives and society in this century and beyond.
One very important sector that will be impacted by more extreme heat events is the healthcare sector. The serious health effects of heat exposure are discussed above, and dramatic events like the 2003 European heat wave serve as testament to the dangers posed by the events, yet the fact remains that many cities, including those in the U.S. are simply not prepared to deal with the health impacts of a prolonged heat wave (Luber et al.). While the number of fatalities for severe events may be significant, the fact is that the total amount of people requiring medical attention due to heat exposure may be enormous. Public health and emergency services would likely be overwhelmed, which could result in further fatalities and problems. Climate change makes this scenario more likely to occur, while at the same time, demographic shifts in the developing world towards an aging population increases the percentage of the population at significant risk. Ultimately, steps must be taken by public health and emergency response officials to revise current response plans and develop new methods of dealing with, and making the public more aware of the dangers associated with future intense heat wave events.
In addition to the direct on health and health services that can result from extreme heat, there are heat related illnesses and deaths that will increase with the rising temperatures. Climate change will cause human health problems related to dirtier air and water, more flood-related accidents and injuries, threats to food supplies, stress on native and domesticated ecosystems that either purify our air and water or provide food.
There may be an increase in infectious diseases due to less availability of clean water and sanitary conditions for medicine and standard living. This is much more of a concern in parts of the world other than the United States where public health systems are not as structured and available. Even in the US, there will be a stress on public health facilities in areas that are particularly vulnerable to extreme heat conditions. In areas of the southern United States there are high levels of humidity coupled with extreme temperatures that put these people at risk. Also, in areas prone to flooding will be increased indirect health problems that will be exacerbated by the increased temperatures and more erratic weather patterns. These indirect health risks can be mitigated by preventative measures against climate warming, which will surely be less costly than trying to fix the problems after they’ve happened.
Agriculture is another sector of society that will be greatly affected by climate warming and weather extremes. Farming productivity depends on steady climate with steady characteristics such as temperature, rainfall, levels of carbon dioxide, and ground level ozone. These levels have already been changed by human activity and with increased climate and more erratic weather; they will continue to become more intense and potentially harmful. In addition to the heat affecting the farmers, the climate will affect water supply and soil moisture, which in certain areas can have a ripple effect on wastewater run-off and sewage treatment—both of which can become significant health risks.
In developed countries such as the US, the most common method for coping with extreme heat comes in the form of electric Air Conditioning. This is not a technology wide spread in less developed countries, so is generally limited to developed countries as a widespread method for dealing with heat related health risks. The increase of climate variability and more extreme heat waves will come with an increase of the use of air conditioning, which will put some stress on the energy sector. With rising energy costs, there will be some incentive to avoid the preventative measure. Just like when rising gas prices force drivers off the street, some people may choose not to use air conditioning if it becomes more costly. This could put people at risk especially in particularly vulnerable areas.
While there is definitely a continuing pattern of increased temperature and more erratic weather patterns, there is also a decreasing vulnerability to heat and heat related risks. These risks are certainly more of an issue in poorer countries, but will become more of an issue in the US as the climate intensifies. There will be a balance between energy conservation and other preventative measures to prevent further man-induced climate change with how we choose to deal with the risks that are already present and will worsen with climate change.
This post was written by Daniel Sugar ’12 who is majoring in Environmental Studies and Nick Horsburgh ’12 a double major in Environmental Studies and Psychology.
Takahashi K, Honda Y, Emori S. Assessing mortality risk from heat stress due to global warming. J Risk Res. 2007;10(3):339–354.
Luber G., McGeehin M. (2008)Climate Change and Extreme Heat Events. American Journal of Preventive Medicine – November 2008 (Vol. 35, Issue 5, Pages 429-435, DOI: 10.1016/j.amepre.2008.08.021)
Huang C., Gerard Barnett A., Wang X., Vaneckova P., FitzGerald G., Tong S. (2011) Projecting Future Heat-Related Mortality under Climate Change Scenarios: A Systematic Review. Environmental Health Perspective. December 119(12): pg 1681-1690.
Heat waves, Centers for Disease Control and Prevention. http://www.cdc.gov/climatechange/effects/heat.htm