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The faintest ink is stronger than the strongest memory — paraphrasation of a Chinese proverb In the world today, we have data galore, and yet many issues of substantial public policy are decided largely through the perceptions of the deciders, whether the issue is economic, climatic, or otherwise, and whether or not the perception is substantiated by the data. I write this post on the presupposition that the truth still matters, though some cynics may argue that narrative is now everything and reality is nothing. Part of the problem is that data is meek and tends to be overwritten (even among the scientifically literate and open-minded) by anecdotal-type perceptions that are dominated by memorable events and are in many cases not representative of the climate at a particular time and place. As a plausible hypothetical, the one year when there were two large snowstorms a week apart, and not the 5 years in between with no such storms at all. One recent study showed that perceptions of weather 5-20 years prior were pretty far off (the only category where people had any skill at all was for recent summer temperatures), except for flashbulb memories on personally momentous days, such as Danes' very accurate recollections, decades later, of the weather on the days of the German invasion and liberation of their country during WWII. For flashbulb memories, bias — where it exists — tends to be positive when moods are high (liberation) and negative when moods are low (invasion), termed the “pleasantness bias” by psychologists. In line with this, respondents from Colorado stated the weather on Sep 11 was worse than average, although in actuality it was sunny and warm across nearly the whole of the United States. These misperceptions are quite likely a function of several factors, such as the human tendency to remember the most ‘impressive’ thing (as it makes a better story), and the survivalist need to remember as much as possible about the conditions that surrounded an extreme, so as to be prepared for its next occurrence. People, not being machines, are also subject to heuristics like the availability heuristic of extending recent trends into the future, and in fact we often have more-accurate memories when the weather is pleasant.  An example of the corruptibility of human perception of weather & climate issues: for people who are on the fence about anthropogenic climate change, the percent professing belief increases linearly with recent temperature anomalies (Source: Hamilton & Stampone 2013, "Short-Term Weather and Belief in Anthropogenic Climate Change"). As a result, memories will never be entirely representative; however I think there are ways to leverage them to help people better understand their “personal climate history”, by linking their memories more clearly to the supporting data. For example, by pointing out where their memories and the data line up (and thus where their memories provide local color to the data), and where they don’t musing about the reasons why they remember something that is on the whole different from what actually happened on the preponderance of days. Establishing a trustworthy and viscerally true-seeming linkage between data and perception is in my view key for determining whether climate events, whatever and wherever they are, will be responded to proportionately and appropriately for a given location. One step in the direction of remedying this issue is the Common Sense Climate Index [CSCI], developed to quantify the 'feeling' people have as to whether or not the climate in their area has changed significantly during their lifetime. It is fairly simple in concept: it compares average temperatures and the frequency of extreme temperatures to the values they had in a baseline period, e.g. 1951-1980. When the index in a year exceeds one standard deviation relative to the baseline distribution, that means the year's temperatures would have been expected only out of every 6 years previously, and the devisers of the index presume this difference is large enough to be noticed by the casual observer. Four illustrative figures of the index are shown below; almost the whole world exceeded 1.0 in 2016, and it's been at or above 1.0 in recent years for the world, the United States, and many individual cities. Some areas, particularly those with high interannual temperature variability or land-atmosphere interactions, like the US High Plains, have yet to see a consistent upward trend. Endeavors like the CSCI are no doubt beneficial in the communication of science at a gut level, but this is not to say that memories should be discounted or considered passé as a mechanism of understanding climate. On the contrary, they play an essential role by filling in where data could not be obtained any other way, or exists but is of uncertain quality. A study in Iceland gives the example of diarists recording glacial positions, or encountering polar bears where none now exist. As this type of information is inherently qualitative, it is especially valuable when it describes something binary, where the accuracy is hard to dispute — someone either saw a polar bear or they didn't, no room for ambiguity.
Also, memories of climate are significantly better than those of weather, particularly among people who work the land and have a good sense of conditions in a place over multiple generations, and who have precise and unambiguous points of reference that they note as a matter of habit: dates of ice breakup, dates of spring planting, locations of glacial tongues, etc. Even so, quantitatively, the best correlation between recollection and fact is pretty imperfect. I'll close this post with some thoughts on how an index like the CSCI could be improved. Very simply, breaking out the components would allow people to see for example how extremes or particular months have changed in their region, helping them gain insight into the present climate (e.g. 'this past December seemed very unusual -- was it really?') and connect it with their own past. Another modification could be customizing the index based on a basket of indicators in each region that are regionally meaningful — special events, ski-resort opening/closing dates, days of snow cover, leaf-out dates, when the window A/C has to be brought out of the garage, the first autumn night requiring a winter coat, etc. Ideally, this would make the index maximally relevant to everyone's lives. Shifting the reference period for people of different ages, or those who have moved, would also help accomplish that goal. Finally, using more crowdsourced data, in the CSCI and in general, would likely stimulate greater interest and investment in local-climate problems, as people are always more emotionally tied to data they have a hand in producing and that they know matters to them. Scientists are trained to think that all data matters, but outside of science the relevance has to first be felt in order to be believed.
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As humans we've been engaged in unplanned terraforming for many years, as I discussed in a post a few months ago. This has come in the form of direct changes to the land via agriculture, logging, and urbanization, and (more recently) indirect changes via greenhouse-gas emissions. The direct changes are more localized and intense, while the latter are generally regional-to-global and comparatively modest. Within each category of change, there are a range of mechanisms at play, from albedo feedback to land-atmosphere interaction effects (on soil moisture, dust, etc). Inspired by a thoughtful piece from a few weeks ago, here I'll focus in particular on desertification -- this focus also helping to set some reasonable parameters on the scope of a single post. One of the core problems with desertification is the phenomenon known as "dry get drier, wet get wetter", which is at its heart a consequence of a strengthening of the water cycle in a warmer climate. This concept, while well-supported theoretically, applies to observations only in certain areas of the globe (see figure below). However, it's also worth noting that much of this non-application depends on the exact definitions of 'wet' and 'dry' used: for example, the relatively dry subtropics, like the Mediterranean, are indeed expected to dry further as this century goes on, but are considered 'wet' by that paper's reckoning.  Observed trends in precipitation from the mid- to late 20th century, combined with climatological moistness/dryness information to categorize regions according to whether they obey the 'dry get drier, wet get wetter' paradigm. From Greve et al. 2014, "Global assessment of trends in wetting and drying over land." If we know deserts are encroaching, on farmland and cities alike, what can we do about it? In a sense, the forces enabling us to "turn back the deserts" are the same as those that we leveraged to cause the changes in the first place, and they are familiarly modern: enormous sums of money, massive spatial coordination, and skillful biophysical and climate models that allow for an understanding of how to optimize resources (e.g. the most-strategic locations to plant trees or to construct irrigation systems). Many of the modifications of course involve the areas surrounding cities, which are much larger and often easier to change, as implementing a different tilling method or planting more trees involves relatively few people and little cost compared to dealing with thousands or millions of individual units in an urban area. Perhaps the best-known example of what could be considered purposeful terraforming is the remarkably successful shift in agricultural practices in the US High Plains in the mid-20th century. Following suspicions that human mistakes were to blame for the severity of the Dust Bowl (later proved correct), agricultural-extension efforts spread the gospel of practices like not leaving freshly tilled soil exposed to the wind. These changes were tested in the 1950s drought, which based on the SST pattern alone would have been equally bad or worse than the 1930s, and the result: no sad families leaving Oklahoma in beat-up cars. Mission accomplished.
While primarily affecting rural residents, cities are of significant interest in the desertification problem because a. they are centers of people and resources, which suffer the most in absolute numbers when dust chokes lungs or shuts down businesses, and b. they are inextricably connected to the surrounding landscape. As a neat illustration of the latter point, a study in Iran directly connected urbanization to desertification through the greater wealth of urban residents, and their correspondingly greater usage and therefore wastage of water. Cities are also in some sense useful laboratories for studying aspects of desertification in microcosm, given that they nearly always have higher temperatures and lower moisture than neighboring areas -- due in part to the urban-heat-island effect and in part to the lack of permeable surfaces wherein moisture can be retained.
Finally, thinking abstractly, cities are instructive in a way because they represent the most complex systems we as a species have ever constructed, and their elaborate infrastructure and balancing of many interests perhaps can provide a sort of framework for how to go about tweaking the analogously (but much more) complex climate system. These viewpoint has even made it up to the stodgy folks at the United Nations Environment Programme. While I believe the overall situation is serious, it merits optimism. That being said, far-fetched plans such as towing icebergs to the Persian Gulf, or building mountains there to squeeze out moisture, will never happen in the foreseeable future – even gushers of oil money just aren't enough to be able to terraform on those kinds of scales with anything like current technology. Besides, shifting cartography is a matter not just of physical geography, but of social and geopolitical geography, and this truism has inspired some very specific meditations on what it all means. A more-realistic prediction would be that in desertifying regions, cities themselves will change to match their surroundings and remain sustainable -- as one small example, constructing buildings from naturally occurring (and naturally insulating) sand. Regardless, industrialization, deforestation, and urbanization will continue apace throughout the developing world, so like with greenhouse-gas emissions the real question with terraforming is not whether it will occur to any substantial degree in our lifetime, but whether it will be planned or unplanned, and whether we will be prepared for the changes it will wreak.
A place for experimentation, detached from the real world -- this is the sort of image that the word 'laboratory' conjures. It has been said that we are engaged in a planetary-scale experiment through our greenhouse-gas emissions, even if this experiment is unplanned and undirected. As we are of course very far from understanding the mechanisms of global climate in anything approximating completeness, in some sense any change we cause is an experiment; it's just that the more intense the experiment, the harder it is to pull the 'stop' lever. This notion of undirected experimentation is frequently invoked in the context of discussions about geoengineering, as a rebuttal to the argument that geoengineering is dangerously artificial. So this line of reasoning goes, experimentation is happening anyway.
As I've written about in many different facets here before, whatever is going on is certainly going on to a greater degree in urban areas. After all, aside from emissions resulting from land-use change (e.g. deforestation), most causes and effects of anthropogenic climate change are concentrated there -- a direct result of population density. And the differences are not trivial: the magnitude of the urban heat island of a typical large city is on the order of 2-4 C, in comparison to about 1 C of global-average temperature change since 1900. In fast-urbanizing areas like China, large cities are not only warmest, but are warming fastest; as a global average, though, cities have not materially affected the existence or measurement of large-scale warming. Taking all this into consideration, we can say that cities are ahead of the curve in terms of previewing the effects of a more intensely developed world, which can be conceived of as an "urban dome" environment. Within this experimental 'dome' -- distinct from an urban heat island as it encompasses variables other than temperature -- conditions can differ in many respects from those outside it. For instance, in a case study in Baltimore, city-center CO2 was about 100 ppm (or 20%) higher than in nearby rural areas. Precipitation is generally enhanced over and immediately downwind of cities, a result of atmospheric instability caused by urban heating. Compared to temperature and precipitation effects, air pollution is even more tightly concentrated, as shown in maps like this, wherein major urban (as well as industrial) areas light up among a low-level rural background. In fact, documented cases of concern over air pollution (primarily from burning wood, and, later, coal) go back to ancient times, and extend through medieval ones, all well before widespread industrialization. John Evelyn wrote, "One day, as I walking in Your Majesty's palace... a presumptuous smoke did so invade the court... that men could hardly discern one another for the cloud"; he continued, "And what is all this, but that hellish and dismall cloud of sea-coal... a fuliginous and filthy vapor" which (couched in terms engineered to tug on regal 17th-century heartstrings) "endanger[s] the health of the king... and sullies the glory of this imperial seat." 
One experiment begets another: Buckminster Fuller's proposed dome over midtown Manhattan, intended to protect the citizens of those neighborhoods from the environmental consequences of the activity necessary to support their energy-intensive existence; their neighbors outside the dome are presumed to have to fend for themselves. Source: The Gothamist, "The 1960 Plan to Put a Dome Over Midtown Manhattan."
Another way that cities are a natural experiment is with respect to ancillary changes in the rhythms of life. It's not just people waking up at 5am for an hour-and-a-half commute that's unnatural; even vegetation experiences discernable and significant changes in phenology. Eli Melaas from Harvard found differences of up to several weeks in leaf-out between street trees and urban woodlands in Boston -- evidence of "micro urban heat islands" -- plus another week or so between urban woodlands and rural woodlands. Temperature and streetlights combine to fool trees into acting as if they were several hundred miles equatorward of where they are. [This interchangeability between urban heating and large-scale temperature gradients will be explored more in a post in the near future.]
In many respects (and not coincidentally), the changes predicted worldwide in the coming decades and centuries are already manifest in cities. One example is warming that is strongest at night and in winter. This means a much longer growing season and a poleward expansion of arable areas. Another robust prediction of climate models is a global intensification of precipitation where it occurs (the old "wet get wetter, dry get drier" mnemonic) that is also already borne out by urban precipitation records, as briefly mentioned above. On the demand side, it would be reasonable to expect a continued decreasing of economic intensity of emissions as urbanization and energy-sector efficiencies progress, as has been already observed both over time for a given region as it develops (left interactive image below), in step with the close relationship between development level and emissions intensity (right image below).
Of course, having a preview of possible conditions that generally confirms our model predictions, while helpful, doesn't constitute a prescience that one should place all their bets on. For one, having a warm city immersed in an unchanging countryside is qualitatively different than having an entire region that's warming, with an even hotter city within it. And the future form of cities is not necessarily essentially the same as today's -- to give one example, driverless cars could enable drastic reductions in paved surfaces, and thus increases in urban albedo, which together with green roofs could alter in large part the city-countryside contrast that currently does so much to drive urban heat islands. Even with perfect knowledge of the inner workings of the climate system, throwing in human behavior makes for a meta-system far too complex and dynamic to confidently predict its direction with anything more than broad strokes. But having urban areas as laboratories at least enables an inkling of what to expect if the remainder of the 21st century, and the 22nd, proceed as the 20th and the 21st so far have done. The lessons we can draw from this experience is that 'business as usual' is climatologically starting to take us down the path of the unusual. 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).  US cities are broken down into more- and less-polluted halves, and the percent black of each half is compared. Any circle above the 1-to-1 line indicates that the more-polluted half has a higher percentage of blacks than the less-polluted half. Source: Ash and Fetter, 2004. 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. |
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