From: jgacker@news.gsfc.nasa.gov (James G. Acker) Subject: Health & Amenity FX: Kalksteins' review Date: 19 Apr 1996 15:09:19 GMT Message-ID: <4l8aav$np0@post.gsfc.nasa.gov> The following is an informal review of Dr. Thomas Moore's manuscript "Health and Amenity Effects of Global Warming" provided by Dr. Laurence Kalkstein of the University of Delaware, Newark, DE. Dr. Kalkstein's research was described in an article in _New Scientist_ magazine about heat-wave related deaths. (September 9, 1995 issue). Dr. Moore has responded to this review, which will be found in a subsequent posting. Both documents will be made available on Rich Puchalsky's Web page and linked to the on-line version of Dr. Moore's paper. ------- Thanks for the opportunity to review the Moore manuscript. I will limit my remarks to the section on "Health Effects"; I am not qualified to discuss the economics in the section on "Human Well Being". As you can imagine, I disagree with much of what Mr. Moore has to say. I believe that his approach is flawed, and this has led to misinterpretation of results. Let's separate the two issues he discusses. First, how does present-day weather affect mortality? Second, what will global warming do to these results? Mr. Moore begins by noting that retirees "...flee to southern and warmer locales," implying that they enjoy warmer weather better. Certainly they enjoy warmer weather better in the winter, but certainly not in summer. Do people move to Phoenix to enjoy its summer climate? How about southern Florida? In fact, Mr. Moore should recognize that many of these people are snowbirds, and they "flee" back north during summer if they can afford to. Even with possible air conditioning mitigation, I am quite certain that most people would rather not stay in these summer climates. Let's first discuss his procedures to evaluate retrospective impacts of weather on mortality. I see the following problems with his procedures. 1. Mr. Moore only uses three years of data. Most studies which evaluate weather/mortality use many more years. Thus, his sample size for deaths and weather data is only about 36, really too small to draw proper conclusions. 2. Importantly, Mr. Moore uses monthly means and totals as his variables. There are real problems doing such a project in this manner. For example, he has removed the daily variability which is so important in evaluating both weather and mortality data. If he had looked at daily data, it would have been clear (actually unequivocal) that daily death totals rise enormously during days when it is very hot. All of this is lost with a monthly means approach. So, if there were six very hot days imbedded within a rather innocuous month, the variability associated with these six days would be lost. We acknowledge in our research that mortality rises on only about the 10 percent hottest days in the summer; Mr. Moore cannot evaluate weather "thresholds" which lead to these increases by using monthly data. 3. Mr. Moore lumps winter and summer data together. This is a serious flaw, as different mechanisms affect mortality across the seasons. In summer, he is correct in noting that general (baseline) mortality is comparatively low, but he again misses the point involving the very high mortality days imbedded in the record. During winter, the baseline is higher, but the day-to-day variability is much less. By not separating the seasons, the results shown in Table 2 are largely driven by the higher winter totals. Thus, even the hottest summer months probably have lower mortality totals than the typical winter months, and regressing against temperature across season yields results that show actual decreases with increasing temperature. Let's put it another way. Assume you have average summer and winter temperatures. Summer mortality will be lower than winter for reasons that have nothing to do with the direct impact of temperature (we'll get to this in a second). Since the summer temperatures will always be higher, and the monthly summer mortality will always be lower, is it a surprise that he found an inverse relationship between temperature and mortality? At the very least, Mr. Moore should have disaggregated by season and used temperatures and mortality totals which are variations from the monthly mean. I would bet him a monthly mortgage payment that his results would be quite different! By the way, I think that even if Mr. Moore used his procedures on winter months only, he would find that the coldest winter months are not those with the highest mortality. The IPCC (1995) study found that regardless of winter temperatures, winter mortality is always higher. In addition, it is often not the coldest winter months which possess the highest mortality from infectious and respiratory diseases, which Mr. Moore isolates as the most important causes of death in winter. Now let's get to the question as to why winter mortality is generally higher than summer. In winter, more people are confined indoors, rendering them more susceptible to infectious and respiratory diseases, as well as possible complications from these diseases which may kill the elderly and other susceptibles. In fact, Table 1 in Mr. Moore's paper indicates this quite clearly. So temperature is indirectly involved, as it confines people indoors in northern and midwestern cities. However, the difference in month to month winter temperature changes things very little. High rates of influenza and other infectious diseases (as well as respiratory and circulatory diseases) are not necessarily associated with the coldest months. Mr. Moore should check this out for a variety of cities to see this for himself. To summarize, it is really only summer mortality which is directly related to temperature. Although some European scientists have found a weak winter relationship, most agree that weather-related mortality variability is much higher in summer. Mr. Moore's results are misleading, as he did not disaggregate by season. Mr. Moore's discussion about vector-borne infectious disease is similarly inaccurate. He cites only developed country examples in his discussion; what about potential spread of vectors in countries where public health facilities and sanitation are poor? Also, the argument that he uses about winter and night temperatures rising more than summer and day temperatures works against him here. The spread of tropical vectors will be enhanced if winter and night temperatures increase, as the freezing line (and other cold-temperature thresholds which retard tropical insect development) will move poleward. The fact that summer temperatures don't increase as much will be a benefit to these vectors, many of which find dessicating summer conditions unsuitable. I will restrict my remarks on the vector-borne disease question, as there are others more qualified than I to talk about this. The impact of a potential global warming on mortality is more difficult to assess. First, the impact of air conditioning and acclimatization is not easy to quantify, and it must be acknowledged that strong uncertainty exists. However, most research shows that summer mortality will increase across the United States, especially in the Northeast and Midwest. This also counters some of Mr. Moore's findings. The frequency of intense heat waves (with temperatures exceeding the threshold) will increase. It is true, as Mr. Moore states, that winter minimum temperatures are expected to increase more dramatically than summer maximum temperatures. But it is not certain what will happen to climate variability; one plausible scenario is that the frequency of extreme heat waves will increase. Although humans may acclimatize somewhat to this increased frequency, the urban structures are not likely to change. Thus, the tenement housing common to vulnerable cities (red brick houses, black tar roofs, windows on two sides only) will most likely remain, and most victims of heat-related mortality are pulled out of these type of buildings (Mr. Moore should talk to the medical examiners of Chicago, Philadelphia, and other large cities). Thus, a summer increase in mortality is likely, as acclimatization will be incomplete. There is much disagreement about the direction of winter mortality if global warming takes place. One argument does agree somewhat with Mr. Moore's assessment - winter mortality might decline to such a degree that it will offset increases in summer mortality (Mr. Moore is incorrect when he states that our studies have, "...ignored the reduction in mortality that warmer winter months would bring." This is always a major discussion among those of us who work in this area, and it has been addressed by the IPCC. We are constantly battling with this question). Studies that discuss a commensurate winter decline under global warming come from Europe, and notably Britain, where summer weather is not marked by the severe heat waves found in the U.S. Most U.S. studies (including additional ones from China and Egypt) clearly suggest that declines in winter mortality will not offset much larger increases in summer mortality. The prevailing thought is that a few degree increase in winter temperatures will still keep people confined for most winter days, and not reduce infectious and respiratory illnesses which lead to many winter deaths. Remember again that the direct relationship between winter temperatures and mortality is much weaker than for summer; this is especially true for infectious and respiratory illnesses. Even if winter temperatures increase more rapidly than summer temperatures, people in New York, Chicago, Philadelphia, and other mid-latitude cities vulnerable to such deaths will still remain largely indoors. Again, I want to emphasize the fact that the summer-winter compensation issue is not resolved, and the IPCC chapter on human health and climate change clearly states this. However, the prevailing thought points to the suggestion that the reduction in winter deaths will not compensate fully for the increase in summer deaths. Larry Kalkstein Dr. Laurence S. Kalkstein Center for Climatic Research University of Delaware Newark, DE 19716-2541 ------- =============================================== | James G. Acker | | REPLY TO: jgacker@neptune.gsfc.nasa.gov | =============================================== All comments are the personal opinion of the writer and do not constitute policy and/or opinion of government or corporate entities.