On the largest scale, we all know from common experience certain aspects of the geography of wealth. For example, that there exists a strong correlation between latitude and wealth. But on the smaller scales, too, we see patterns emerge that are just as strong. For example, whatever way the arrow of causation points, it nearly always results in the poor living in the most climatologically undesirable areas. Perhaps it is that the neighborhoods near power plants, major highways, etc. are cheaper and the poor are shunted there; perhaps it is that the poor are less able to protest and politically prevent the erection of sources of pollution in their neighborhoods. Many examples of both surely spring to mind. In combination, they mean that the poor live in areas where the mortality may be as much as 2.5 years less than the area mean (see figure below).
The wealthy dominating certain climatologically favored areas is hardly a phenomenon of the industrial era. The Latin poet Martial wrote: "While the crooked valleys are crowded in mist, [the villa] basks in the clear sky and shines with a special radiance of its own... From here you can see the seven lordly hills, and can survey all of Rome, the Alban hills and those at Tusculum, every cool suburban spot." A study documenting socioeconomic patterns in American cities in 1880 found that household wealth was positively correlated with elevation -- hypothesized reasons include views, breezes (in a pre-air-conditioning world), privacy, and the prevalence of stagnant water and its associated diseases in the lowlands. To a remarkable degree, worldwide, most slums are in swampy lowlands, from the East End of London to the Lower East Side of New York to Lagos and Mumbai. The wealthy congregate on hillsides, from Mount Royal to Hollywood to Yamanote. Only in unreconstructed areas that are rocky, very steep, remote, significantly colder, or otherwise forbidding, do the poor live at higher elevations. Examples of this include the present-day area of Central Park prior to the park's construction, the favelas of Rio de Janeiro, and the city of El Alto, Bolivia vis-à-vis La Paz in the warmer valley below.
Besides elevation, another strong correlation is between geographical direction from the city center and wealth. Because in the mid-latitudes of both hemispheres winds are typically from the west, pollution from the city tends to be blown to the east, such that from the dawn of industrialization there has been pressure in many areas pushing the poor to those disadvantaged areas. The insidiousness of this type of silent urban geographic molding is that once formed, it would take enormous effort and expense to change it — so it endures, at great social cost. The wealth geography of London has hardly changed in a century (also see below), even though in absolute terms the pollution is much less than before (in the case of London, the East End has been doubly disadvantaged by the fact that the Thames flows from west to east, transporting foul water in its direction).
It is fascinating to note how technological advances have muted some of the traditional correlations, while future factors such as sea-level rise will shift the goalposts of the game yet again. Reductions in pollution, plus better filtration, have in many places lessened the imperative for avoidance of the city centers. Air conditioning has reduced the climatological incentive to have breezy, cool buildings, and encouraged the growth of insufferably hot cities such as Phoenix. Mosquito control, vaccines, and improved drainage and hygiene more generally have, in the developed world, mostly eliminated the intra-urban correlation between elevation and stagnant water. This has meant new construction in many areas is often in these previously undesirable or simply unbuildable areas, although it may take hundreds of years for the shift to complete. For example, in Midtown Manhattan the bogs were drained and the vegetation felled in the 19th century, yet the undesirable label stuck with the lower ground along both rivers, leading to these areas being filled with tenements, auto-body shops, warehouses, and the like throughout the 20th century. Only now is wealth pouring in and tall buildings being constructed. Yet sea-level rise means that inevitably, perhaps within decades, these gleaming new buildings may be threatened and (to speak punnily) the tide may turn again on these reclaimed lowlands.
While the prototypical "castle on a hill" urban template is long gone, there were solid climatological reasons for the wealthy to retain the high ground in most places, and relegate the poor to the low ground. This is primarily a response to the strong correlation of elevation with desirable traits such as clean air, water, and safety from flooding. While recent advances have rendered most of these reasons obsolete ipso facto, the inertia of urban geography is great, and there are additional factors such as the siting of polluting industries and activities. As long as it continues to be politically palatable to favor the rich over the poor, this corrosive environmental inequality will endure. But the better our understanding of its patterns, and the microclimatological influences that are the mechanisms for its deleterious effects, the better those effects can be managed and the tyranny of place less of a strong force in shaping people's lives.
Ever since the discovery of the urban-heat-island effect back in the early 19th century, we've known that the geography of our settlements influences their climate. There are many examples, from very high temperatures to wind speed and precipitation. And it turns out that the effect of village- and agriculture-related decisions goes back even farther -- in fact, it's traceable back to about 1000 BCE (also see figure below). At the same time, in projects such as coastal redevelopment, Gulin New Town, and planning strategies for slums in the developing world, design and planning has the power to directly alter the physical contours of the world, and beyond that to inspire awareness and organic change of the intimate link between climate and human decisions. These kinds of efforts aim to envision neighborhoods that have less impact on the climate, both in terms of local heat-island-type effects, and in terms of their contributions to global greenhouse gases. For example, a project in the Netherlands proposed such ideas as coniferous trees along roadways to filter pollution and to block noise throughout the year, and (to build on a timeless Dutch practice) canals or other waterways that provide moisture for the vegetation, evaporative cooling for hot days, and recreation pathways for commuting and exercise. They term this suite of concepts -- applicable to new or existing development -- as "making a city climate-proof". While this is not strictly true, of course, this type of urban planning does fall under the category of "vulnerability reduction" and is gaining steam in the planning community.
Cumulative (top) and annual (bottom) anthropogenic carbon emissions from land use (primarily deforestation). The red and blue lines represent two different simulations. The invasion of the Americas and the subsequent precipitous drop in population and cultivated area there is seen as the sharp drop around 400 years ago in the blue simulation. Source: Kaplan et al. 2010.
Ironically, multipurpose solutions (the Dutch canals mentioned above, or Masdar City in the UAE) are often a return to traditional ideas that gave way in the 19th and 20th centuries to modernistic approaches which frequently harnessed the technological optimism of the day to assert freedom from the tyranny of local natural conditions, in the form of standardized components and techniques. Arguably, this line of thinking can be seen in many facets of decision-making at the time, from the imposition of a street grid on natural topography to the belief that uniformity and predictability were desirable in every facet of life. Now that nature is less a thing to conquer and more a thing to preserve, the logic that resulted in our imposing our will on it is no longer there. The Earth is against the ropes, bruised and bloody, still standing but clearly hurting -- it would be heartless indeed to continue pummeling it. While the Earth is a big place by any measure, the collective decisions of nearly 7.5 billion people are more than enough to affect its course. No place is remote enough to be safe from our influence, for better or worse. Lately the emphasis has been on the "worse" aspect but the "better" part should be remembered too -- even if that betterment is primarily about damage mitigation.
Essentially, it could be said that we eventually wised up to the notion that fighting nature was a waste of resources in comparison to trying to live in harmony with it. Depending on the identity of the actors, the motivation behind this shift can range from hardheadedness to idealism, but to a large degree urban planners have converged on a set of principles expounded in initiatives like China's sustainable-development program: enlarging and improving green spaces, minimizing distances traveled by nurturing neighborhoods with distinctive identities and full suites of services, expanding public transit, designing systems to run smoothly using renewable energy, and creating or overhauling buildings and infrastructure to use the least amount of water and energy possible. The hope is that such cities will set off a 'virtuous cycle' where they have less and less impact on the environment, and so will have less and less energy/water/land requirements, thus having an even smaller environmental impact. Combined with a population that is still growing but expected to level off within a few generations, there's reason for optimism about the peaceful co-existence of our species and the planet that nurtured us. While perhaps ultimately we can build extraterrestrial cities (no need to worry about the vagaries of climate if you can make your own instead!), the tribulations of Biosphere 2 -- the largest sealed-environment experiment thus far -- indicate focusing our efforts on the planet we already know and (sort of) understand will probably be more fruitful.
Though this post is about heat waves, the allusion to the space-time of theoretical physics is not accidental. What happens across space matters if large areas are affected at the same time -- a bending of the fabric of the climate system, if you will. In this abstract realm, spatially large, long-lasting, and intense heat waves are the dominant players, and these are also what matter most from a societal-impacts point of view. A heat wave striking both Chicago and New York, or a hurricane lashing both Kolkata and Dhaka, or a drought afflicting both Ethiopia and Kenya may be of more concern than a more-concentrated event of greater magnitude. It's the full spatiotemporal picture, multiplied by other factors like population affected, that's in some sense the true measure of an event.
Space-time patterns, while powerful in a predictive sense, do fade. As you go farther apart, things are generally less connected. The first figure below illustrates that for heat waves -- the dates of LA heat waves have no connection whatsoever to those in NYC. But at the same time, this correlation is not entirely symmetric either; it's oriented preferentially in certain directions, in this case east-west, such that heat waves in Detroit resemble those in NYC Central Park more than heat waves in Virginia Beach, because it's more common for the same pressure system to cause a heat waves in Detroit and NYC than in Virginia Beach and NYC. Any major geographic feature, like the Central Valley, will have this asymmetric-correlational effect. Temperatures at beaches 100 miles apart will for the most part be more similar to each other than to those 10 miles inland from either location, because the common effect of sea and land breezes will dominate any effects resulting from differences in terrain or cloudiness. Besides geography, the other major source of climate 'action at a distance' is teleconnections -- both ones you'd expect from first principles and those that are somewhat more head-scratching (why the correlation off of Argentina??). While Einstein may have been wrong about quantum entanglement, he was right in the climatic sense: 'action at a distance' only appears that way from the ground, without the benefit of being able to observe the ocean and high atmosphere that are communicating information from one place to another. It may be a long game of Telephone, but some sort of message eventually gets through.
Space and time are correlated with other dimensions of weather events also-- for example, in the Northeast US (see second figure below) as well as in the Czech Republic (and likely throughout the mid-latitudes, if not the world), larger heat waves tend to be hotter. It's still uncertain as to whether this is a causation or merely a correlation, but nonetheless it implies that the stress on systems like the energy grid increases exponentially as heat waves get more severe. (But not necessarily that this exponential increase will occur in a warming climate, because most scientists' expectation is that dynamics will be relatively constant, i.e. a heat wave of the same size will increase temperatures by the same factor as now relative to climatology — that is, they won't somehow become 'more efficient' at transporting heat and moisture, just that there will be somewhat more of it available.)
One thing we know for sure, direct from observations, is that weather patterns of many sorts tend to 'pulse'. Rarely is there a monotonic change, or an abrupt onset with no subsequent slippage. This is as true for glacial onsets and terminations as it is for seasonal precipitation, and down to the timescale of minutes as shown in this hypnotic simulation. This pulsation is to be expected in a complicated system that never reaches true equilibrium because the forces that guide it are always themselves changing, even if that just means shifting slightly in position or strength. Such is the case for the infamous 2003 heat wave, nicely analyzed in many papers, but the Feudale and Shukla 2011 one is particularly relevant to the discussion here. Those authors found the focal point of the most-anomalous heat moved around Europe during that summer, and its movement could be summarized by two "empirical orthogonal functions" (see below) that represent prominent decompositions of the variability: the first in Central Europe with cooler air along the coasts, and the second over France and Benelux with relief from the heat in Russia and the Caucasus. These EOFs and the time series of their relative presence/absence are shown below. In this context, it is striking to note how, within what is popularly and even meteorologically considered a single extreme event, multiple different 'flavors' were observed, dramatically changing the experience of the summer depending on where exactly you were.
Another perspective on a similar event, this one occurring in 2010, is provided by a 2011 paper by David Barriopedro et al. They had the idea of representing the heat wave's combined spatial and temporal strength and persistence in one elegant figure that shows at a glance how large the heat wave was, on what time scale, when its peak occurred as measured by this metric, and overall how intense it was (by comparing to the same chart for the aforementioned 2003 European heat wave). This figure is included at the bottom of this post to marvel at the genius of.
With so many different dimensions and variables in the climate system, in some ways it's a wonder there aren't more than 26 heat-wave indices (Tables 2 and 3 of this paper) floating around. An analogy to economics seems appropriate -- an economic index could be tailored to perfectly match, say, your family's finances, including every DVD purchase and late-night run to KFC, but it would be quite unusable for anyone else. Similarly, making a very vague index is the more generalizable and also the least applicable to any one person or situation. A middle ground is necessary, to be able to usefully distill the great complexities of the climate system into something understandable -- because only once it's understandable, even with some degree of simplification (as with the potentially quantifiable autocorrelations given at the start of this post), can optimal decisions be made taking into account its many variations and apparent vagaries. When our species masters spacetime we may decide there's more-exciting things to do in the universe than investigate the details of terrestrial heat waves in old-fashioned nation-states, but who knows... even with competition from wormholes and time travel, they could well prove to be a subject of bottomless fascination.
I went to a cool talk recently, titled COOL, that featured Stan Cox, a geographer interested in the cultural & environmental context & effects of A/C usage. He noted, astutely, that "the middle of a heat wave is the worst time to talk rationally about this". Within the US and other industrialized nations, A/C has become nearly universal except in the coldest regions, and in fact much of our lives are predicated on the existence of it in nearly unlimited quantities, so that it's hard to imagine doing without it. For instance, the Sun Belt commuter who in the summer moves between air-conditioned buildings in an air-conditioned vehicle, a daily routine that exposed to the heat of the untreated air would be intolerable. Also, many new high-rise buildings are built without even the capability for natural ventilation on the scale that would be needed, on the presumption that it never will. The huge role of A/C in economic development, particularly of the American South, led the history professor Raymond Arsenault to quip, "General Electric has proved a more devastating invader than General Sherman."
The below figure shows the dramatic decrease in heat-related mortality in NYC over the decades of the 20th century, beginning in earnest in mid-century -- coincident not just with the advent of widespread A/C, but also with the universality of electricity (and thus fans, refrigerators, and reliably cold water); with greater numbers of sidewalk trees; and with reductions in cardiovascular disease, a major risk factor for heat-related mortality. [The figure is based on epidemiological work suggesting that publicized numbers of heat-related mortality are underestimates because they mostly represent heatstroke and not the more-common case of heat strain exacerbating underlying health problems.] To do a back-of-the-envelope calculation, a city of 8 million and a life expectancy of 75 years (i.e. NYC in 2005) should average 290 deaths per day; a city of 4 million and a life expectancy of 55 years (i.e. NYC in 1905) should average 200 deaths per day. Combined with an annual maximum daily-average temperature around 31 C, these curves mean total deaths on the hottest day alone fell from 500 in 1905 to 350 in 2005, and excess (heat-related) deaths fell from 300 to 60. Conservatively, anti-heat technology (broadly speaking) has saved hundreds of lives per year just in NYC relative to a century ago.
Curves estimating the total number of deaths in New York City for different hot temperatures over the past 110 years. For example, in the 1940s the city would experience roughly twice as many deaths as normal on a day with a mean temperature of 31 C. In a city of 7 million people, this translates to 550 deaths vs. 275 normally, or a daily heat-related death toll of 275. Source: Petkova et al. 2014.
However, the talk also emphasized the more-deleterious effects of air conditioning, both well-known and less-known: energy consumption and resulting pollution (though on extremely hot days outdoor ozone is more of an issue), and freon that contributed for many years to the creation of the 'ozone hole'. Then there are social effects: for one thing, A/C may encourage social isolation, and for another, people who work outside or in factories have not benefited during their workday from the universalization of indoor A/C, but nonetheless experience hotter temperatures due to the waste heat from A/C units and the greenhouse gases to whose emission they contribute -- a bit like the Pacific Islanders who have contributed least to global emissions but have the most to lose from sea-level rise. Maybe, as the moderator of the Q&A discussion suggested somewhat fancifully, outdoor workers can someday have "little air-conditioned bubbles" akin to how clothes are a efficient personal 'warming bubble' in winter. [Update, 9/6/16: with new cooling fabrics, this idea is perhaps not too far away after all!]. This issue is of concern not just out of fairness, but because many of these outdoor workers are essential but invisible cogs in the modern urban postindustrial economy: they are construction workers, delivery personnel, etc. The COOL talk was held on a hot and humid day, and while bicycling home I began paying more attention than before to the significant number of deliverypeople on bicycles, for whom the heat was not a 15-min blast as for me, but a grinding background presence to their hours-long shift. Ironically, many of them were making deliveries for companies (e.g. organic food & restaurant companies) that bill themselves as not only convenient but environmentally friendly and socially just -- yet upon closer inspection these claims begin to waver, like heat mirages. On the other hand, A/C can aid in reducing inequality as well; despite the efforts of "open-air crusaders" in the '20s, schools (at least in the North) have been some of the last buildings to have A/C of any kind installed -- 25% in NYC still lack it, often because of inadequate electrical systems. Uncomfortably high temperatures have a clear effect on academic performance, and it is not a stretch to imagine how this sort of 5% or 10% disadvantage can add up over time to affect students' career trajectories, in a world where the difference between acceptance and rejection is often just several percent.
As with many advances in efficiency or capacity, A/C's decreasing cost has led to perverse increases in usage, often to the point of wastage -- as, Mr. Cox pointed out, any office worker who's worn a sweater in August is well aware. Combined with figures like the increasing number of square feet of building space per person, it's no wonder that power used to run A/C jumped 37% between 1993 and 2005, even as efficiency increased 28% . The perception of limitless supply of something is often problematic (e.g. suburban sprawl), and in the case of A/C this effect is enhanced by the stubbornness of prestige surrounding the ostentatious use of A/C, as a reporter for the New York Times discovered in 2005, summarizing a round of department-store tours by noting, "The higher the prices, the lower the temperatures." Perhaps this prestige factor is to some degree behind the freezing-office phenomenon as well. Besides ostentation, dependence on A/C (like designing buildings to not allow for natural ventilation even on reasonably temperate days) and ignorance of the electrical demand it produces can combine to lead to a backfiring effect when systems get overloaded and shut down, as in Chicago in the 1995 heat wave, when high demand led to outages and thus for a while in certain neighborhoods no one had any A/C at all.
Mr. Cox argued that a large but unspecified fraction of A/C usage is 'nonessential', i.e. primarily for comfort rather than health, and thus could be made unnecessary with thoughtfully designed buildings, cultural shifts, conscious efforts at acclimatization, etc. In New York City, anyway, I found this to be true: in the past 20-odd years, there have been an average of 1094 hours with temperatures in the 75-85 F range, against just 168 hours with temperatures 86 F or higher. Emissions in both New York City and the United States as a whole have fallen since their peak around 2005, but in terms of going further A/C certainly seems a low-hanging fruit.
Looming over any discussion of the excessive use of something by the U.S. (and there could be many) is the logical desire for aspiring, developing countries to use that thing at the same per capita rate, and the enormous environmental cost that would be borne if that came to pass. And unlike for electricity or water in general, which are in relatively constant demand no matter the climate, A/C is most used where it's hot -- and the poor of today are overwhelmingly concentrated in the tropics. In James McNiven's book "The Yankee Road", former Prime Minister Lee Kwan Yew of Singapore lauded A/C as making his country's rapid ascent to and maintenance of a high standard of living possible, both in increasing productivity and in making the city desirable to expatriates. Temperature does have a real effect on productivity -- Burke et al. 2015 found an annual average temperature of 13 C maximized productivity across the world and across economic sectors -- probably not coincidentally, this is almost exactly the climate of New York City (12.8 C) and London (12.4 C). Mr. McNiven also notes that without A/C, technological and industrial centers like Bangalore and southern China simply would not be possible. But Mr. Cox estimates that if tropical populations were today using A/C at the same rate as the US, global power dedicated to A/C (currently 10% of the total) would increase tenfold -- larger than that for all other usages combined as of today. A/C also has a negative effect on physiological acclimatization to heat, contributing to a cycle of more and more demand driven by physiology in addition to the cycle driven by waste heat and greenhouse-gas emissions.
So A/C is almost like a riddle: essential but superfluous, a luxury and a necessity, a solution and a problem. With all the above considerations in mind, it will have to be part of a larger set of approaches to optimally negotiating the often-testy, always-complicated relationship between humans and the environment.