1.1 CO₂ and breathing

Human respiration implies the insertion of air into the lungs with volumes that oscillate between 500 ml during low breathing rate to around 4000 ml during maximum breathing rate and at frequencies associated with the type of activities that occurs. With this, there is an exchange of gases between the external and the internal environment (Frydrysiak) [1]. This includes the movement of air between the inside and outside of the lungs; the exchange of gases with the pulmonary blood; the transport through the bloodstream to the cells and their subsequent diffusion across cell membranes. These steps allow the consumption of O₂ and release CO₂ in the cells. The cellular respiration is the oxidative metabolism, based on the oxidation of nutrients necessary for the generation of metabolic energy. Naturally, besides the respiratory system, the cardiovascular system, blood circulation and the neural apparatus that regulate functions are essential aspects of energy metabolism. In addition to gas exchange, the respiratory system develops other functions, such as the pulmonary capillary bed acting as a filter for blood, so that small clots, debris or air bubbles are eliminated. The airways are designed to prevent the entry of pathogens into the body; the breathing participate in homeostatic mechanisms such as temperature control, control of bodily fluids and acid-base control.

All this functions and relationships mean that breathing is a powerful indicator of metabolism. Table 1 (adapted from Noriega) [2] shows the typical gas exchanges that occur in the breathing system. Based onthis typical values, the estimated CO₂ flow is 0.035 kg/hr (0.84 kg/day).

Table 1: Gas exchanges in the breathing system.

1.2 CO₂, food usage and metabolism

The CO₂ flow, of course, is associated to food consumption. Table 2, (adapted from Merrill) [3] and [4], estimates CO₂ flows departing from energy and mass associated to typical daily food consumptions in terms of proteins, fat and carbohydrates from animal and vegetable origin These were estimated averaging seven daily nutrient intakes (Merril) [3] and their energy and mass correlates.The estimated average CO₂ generated (0.85 kg/day) is quite close to the value gotten from the respiration gases analysis of Table 1 (0.84 kg/day).

Table 2: Typical mass and energy associated to daily food consumption.

Energy usages have special behaviors. In a particular study of 15 various physical activities of 275 subjects (Seliger) [5], it was found that energy expenditures did not correlate well with the intensity of the motional activity, which suggests that there are more complex physiological and mental influences at work besides observed motion. Illness, previously consumed food and beverages, environmental temperature, and stress levels can affect energy expenditure (Durnin) [6]. Also, the same type of activity may be associated with wide variations in the metabolic response.

Oxygen usage, taken from Table 1 is 0.86 kg/day, quite similar to CO₂ generation. Of this, 0.62 kg/day are used for carbon oxidation and the rest, for hydrogen oxidation of food. The CO₂ generated instantaneously will depend on the type of activity, as each type consumes different amounts of energy. Table 3 presents typical values [4], (Deakin University) [7], (FAO) [8] for a wide set of activities.

Table 3: Metabolic and CO₂ data for several activities.

One important activity is the basal one. Basal Metabolic Rate (BMR), the minimal rate of energy expenditure compatible with life (Durmin) [6], which depends on age, sex, height and weight and is associated with fundamental organs of the body. See Table 4. Note in it, the importance of the brain and the liver, accounting for almost half of the BMR.

Table 4: Energy expenditure breakdown at BMR.

3.1 Relaxed and emphatic states, oxygen use and CO₂ generation

Data shows that certain habits tend to increase CO₂ specific emissions, while other ones tend to lower them. Meditative states generate special metabolic patterns (Farrel) [9], (Ding) [10]. In those, catecholamine levels drop, galvanic skin resistance increases, respiration rate and volume flow decrease significantly without significant change in arterial partial pressures for O₂ and CO₂; there is also decreased vascular resistance, lowered oxygen and CO₂ consumption, and a decline in blood lactate. The person stays vigilant, but the body goes into a state of muscle relaxation. This state, which has been called the relaxation response, in addition to having important influences on physical health, is the initial step defining the physiology of most forms of prayer, contemplation, and meditation across cultures (Wallace) [11].

There is also an especial behavioral state, of empathic nature, which we will call object experimentation. In this state, the person acts as an observer that is able to experiment and feel the situation that is being experimented by another object, (which can be another person or being; a thing; an idea; a situation). The observing person puts her attention on the other being, forgets about herself, entertain herself in any detail that observes in the object and feels how is to be identical to the observed object.

When this is done, intentionally for a short time, the person notes a change in her respiratory pattern, which becomes slower, more abdominal in nature, controlled by the diaphragm and more tranquil and deep. At some point in the process, the observing subject experiments a kind of motion that puts her inside the space occupied by the object.

But not only this, she feels different, close, identified with the object, capable on putting herself in a new perspective, more equilibrate and, in many ways, wiser. She experiences empathy, the psychological identification with the feelings, thoughts, or attitudes of others. It is interesting to note that experiencing empathy, not only with persons, but also with things, beings and ideas, is associated with lower oxygen consumption rates and, consequently, with lower metabolic energies and CO₂ generation.

4.1 Sustainable cities should stimulate good habits that have impact

Now we propose several habits that could be enhanced socially and that are associated with states that generate, as such, lower metabolic CO₂ emissions, either because they are closer to the basal metabolic rates or because they include emphatic or relaxation practices. For each one we give indications of ways in which those habits would have much deeper implications on CO₂ emissions lowering than the habit itself.

With the use of monitoring equipment to measure CO₂ concentration in expired air and respiration cycles, it is possible to provide real data to establish feedback loops between empathic practices, consciousness and lowering CO₂ metabolic emissions.

Listeningto others with attention, especially with empathic attention that pays recognition and appreciation to the other one, not matter what ideas, personal stories, social or economic status the other person has, is a good habit of enormous impacts that have not been explored as much as desired in the practice of human communications or relationships. The usual habit is to judge the other person with hardness and defensive attitudes, to label her with disqualifying names or attributes, to be ready to discuss or contradict her ideas, to be uncompromising, distrustful and unbelieving; all of those are states which demand exited metabolic functioning and excess CO₂ generation. Attentive listening facilitates social encounters, is conductive to learning, to induce compassion and focused attention. It facilitates group work, which will generate creativity and projects oriented towards the environment. We propose this practice, in groups, to originate ideas and designs for the projects a sustainable city requires. We propose to create abundant spaces for group work, conversations and nature contemplation. When listening is extended to nature, this practice calms the mind and induces relaxation states.

Meditation and relaxation practices especially when practiced in group, are positive in all aspects of group and personal human behaviour and have large impacts, even when practiced by a minority of the population. We propose that these practices be taught and encouraged in the educational system and that institutions and companies facilitate spaces and times for the regular practice of their employees and associates.

Conversation and sharing, which includes the idea of friendship, family life, small communities, communal activities, open possibilities to be optimistic and joyful, to develop projects with large beneficial, ecological and social impact. Conversation enriched by empathic attitudes, create high quality attention and peaceful environments. The extreme opposite to this, war, is always associated with major environmental disasters and violence, high generators of excited metabolic states and CO₂ emissions. Sustainable cities must be pleasant and peaceful. An especial situation is the one that occurs with major catastrophes, a constant menace for cities, which in general have negative and unpredictable impacts on the environment. Establishing coherent sharing and communal attitudes is a must for a sustainable city to be able to handle these situations.

Conscious writing, representing, art work and reading will create self-esteem, self-reference, leadership and a sense of compromise. With this we refer to the creation of city narratives and memories that enhance healthy pride, participation and projects that permit establishing personal and group goals and sharing and stimulation of values. We do not refer here to the idea of attaining fame or glory with elite sports or the professional cultivation of the arts (also important, but in general limited to a selected minority). What we propose is a generalized stimulation of good cultural habits that all sustainable citizens can enjoy and practice.

The habit of understanding activities in term of their impact on CO₂ generation and having them in the collective and individual mind as indicators of commitment with sustainability is very good practice. A sustainable city should establish indicators and goals that citizens could understand and help attaining. If people were able to connect the indicators with their habits, they could do something real about that, in comparison to simply seeing the problems as something they cannot confront and, much less, help solving.

With some examples, this idea can be better understood, as shown in Table 7.

Table 7: Example of areas that can be object of establishing CO₂ indicators.

Improving on food consumption habits is an area of opportunity. Eating meat is a very important CO₂ generator. In an analysis of the EU-27 countries, (Schwarzera) [15], beef had the highest GHG (global greenhouse gases) with 22.6 kg CO₂-eq/kg. The consumption of beef meat is increasing at higher rates than the population.

A good habit is to include more protein sources in the diet coming from vegetables or from other meats, so that beef meat is combined with them. On the other hand, the simplest and most cost-effective way to reduce CO₂ food footprint is to minimize food waste. Although not all food waste is under the control of citizens, purchasing, cooking and eating habits can play a large part in reducing food losses. Food waste can generate significant amounts of methane through anaerobic decomposition. In a wet boreal/temperate climate zone, typical methane emissions are about 1.4 kg CO₂ per kg of wet food waste.

We propose the habit of eating slowly and in a conscious way as a very good practice with large implications on metabolism and CO₂ generation. Enjoying and distinguishing flavors, tasting them is empathic, as the observer puts her attention on the act of eating as a gift from life, as a communion with nature and earth, as the result of so many dedicated and loving people working in agriculture, in the transportation, distribution and preparation of food. This empathic attitude, besides diminishing direct metabolic CO₂ emissions, is a driver to avoid waste and to share with others.

A whole set of additional possible habits and good practices could contribute to attain sustainability in a city, among them:

• Tackle problems in a calm, intelligent and conscious way, in comparison to accusing, blaming and using stress generating solving methods.
• Diminish, separate, recycle and reuse waste.
• Seek rational use of water and energy in every human daily activity.
• Seek changes in the smoking of tobacco (and marihuana), or entirely avoid them, as these are bad habits generate huge amounts of CO₂.