Climate resilience

From Wikipedia, the free encyclopedia

 

 

A graphic displaying the inter-connectivity between climate change, adaptability, vulnerability, and resilience.

Climate resilience is defined as the "capacity of social, economic and ecosystems to cope with a hazardous event or trend or disturbance". This is done by "responding or reorganising in ways that maintain their essential function, identity and structure (as well as biodiversity in case of ecosystems) while also maintaining the capacity for adaptation, learning and transformation". The key focus of increasing climate resilience is to reduce the climate vulnerability that communities, states, and countries currently have with regards to the many effects of climate change. Currently, climate resilience efforts encompass social, economic, technological, and political strategies that are being implemented at all scales of society. From local community action to global treaties, addressing climate resilience is becoming a priority, although it could be argued that a significant amount of the theory has yet to be translated into practice. Despite this, there is a robust and ever-growing movement fueled by local and national bodies alike geared towards building and improving climate resilience.

Climate resilience is related to climate change adaptation efforts. It aims to reduce climate change vulnerability and includes considerations of climate justice and equity. Practical implementations include climate resilient infrastructure, climate resilient agriculture and climate resilient development. Most objective approaches to measuring climate resilience use fixed and transparent definitions of resilience, and allow for different groups of people to be compared through standardised metrics.

Definition

Climate resilience is generally considered to be the ability to recover from, or to mitigate vulnerability to, climate-related shocks such as floods and droughts. It is a political process that strengthens the ability of all to mitigate vulnerability to risks from, and adapt to changing patterns in, climate hazards and variability.

The IPCC Sixth Assessment Report defines climate resilience as follows: "Resilience in this report is defined as the capacity of social, economic and ecosystems to cope with a hazardous event or trend or disturbance, responding or reorganising in ways that maintain their essential function, identity and structure as well as biodiversity in case of ecosystems while also maintaining the capacity for adaptation, learning and transformation. Resilience is a positive attribute when it maintains such a capacity for adaptation, learning, and/or transformation."

Resilience is a useful concept because it speaks across sectors and disciplines but this also makes it open to interpretation resulting in differing, and at times competing, definitions. The definition of climate resilience is heavily debated, in both conceptual and practical terms.

Related concepts

United Nations Environment Programme Adaptation Gap Report 2020

Climate change adaptation

The fact that climate resilience encompasses a dual function, to absorb shock as well as to self-renew, is the primary means by which it can be differentiated from the concept of climate adaptation. In general, adaptation is viewed as a group of processes and actions that help a system absorb changes that have already occurred, or may be predicted to occur in the future. For the specific case of environmental change and climate adaptation, it is argued by many that adaptation should be defined strictly as encompassing only active decision-making processes and actions – in other words, deliberate changes made in response to climate change.

Of course, this characterization is highly debatable: after all, adaptation can also be used to describe natural, involuntary processes by which organisms, populations, ecosystems and perhaps even social-ecological systems evolve after the application of certain external stresses. However, for the purposes of differentiating climate adaptation and climate resilience from a policymaking standpoint, we can contrast the active, actor-centric notion of adaptation with resilience, which would be a more systems-based approach to building social-ecological networks that are inherently capable of not only absorbing change, but utilizing those changes to develop into more efficient configurations.

Climate change vulnerability

If the definition of resiliency is the ability to recover from a negative event, in this case climate change, then talking about preparations beforehand and strategies for recovery (aka adaptations), as well as populations that are more or less capable of developing and implementing a resiliency strategy (aka vulnerable populations) are essential. This is framed under the assumed detrimental impacts of climate change to ecosystems and ecosystem services.

It is important to note that efforts to enhance resiliency can result in outcomes that are adaptive, maladaptive, or even both. When considering inequality with adaptation we can focus on distributive justice, the intent of which is to maximize benefits for and promote the engagement of the most disadvantaged communities. Identifying a community or population as vulnerable can lead to biases due to the different factors negotiated in the term vulnerable. Outcome vulnerability (focusing on quantitative measures) and contextual vulnerability (focusing on qualitative measures) are two aspects that must be thought of in unison to achieve a wholistic understanding of a community's vulnerable state. Because one population's level of vulnerability is constantly shifting (as are the threats and impacts of climate change) the efforts to provide adaptive strategies must offer multiple opportunities and outcomes.

Climate change vulnerability (or climate vulnerability or climate risk vulnerability) is defined as the "propensity or predisposition to be adversely affected" by climate change. It can apply to humans but also to natural systems (ecosystems). Human and ecosystem vulnerability are interdependent. Climate change vulnerability encompasses "a variety of concepts and elements, including sensitivity or susceptibility to harm and lack of capacity to cope and adapt". Vulnerability is a component of climate risk. Vulnerability differs within communities and across societies, regions and countries, and can change over time. Approximately 3.3 to 3.6 billion people live in contexts that are highly vulnerable to climate change in 2021.

Vulnerability of ecosystems and people to climate change is driven by certain unsustainable development patterns such as "unsustainable ocean and land use, inequity, marginalization, historical and ongoing patterns of inequity such as colonialism, and governance". Therefore, vulnerability is higher in locations with "poverty, governance challenges and limited access to basic services and resources, violent conflict and high levels of climate-sensitive livelihoods (e.g., smallholder farmers, pastoralists, fishing communities)".

Components

Currently, the majority of work regarding climate resilience has focused on actions taken to maintain existing systems and structures. This largely relates to the capacity of social-ecological systems to sustain shocks and maintain the integrity of functional relationships in the face of external forces. However, there is a growing consensus in the academic literature that actions taken to induce structural changes must also be recognized within the definition of resilience. The three basic capacities that are understood under the common definition are absorptive, adaptive, and transformative, each of which contributes different factors to the efforts of resilience work. This includes the capacity of social-ecological systems to renew and develop, and to utilize disturbances as opportunities for innovation and evolution of new pathways that improve the system's ability to adapt to macroscopic changes.

Key aspects include: how resilience relates to climate change adaptation; the extent to which it should encompass actor-based versus systems-based approaches to improving stability; and its relationship with the balance of nature theory or homeostatic equilibrium view of ecological systems.

The building of climate resilience is a highly comprehensive undertaking that involves of an eclectic array of actors and agents: individuals, community organizations, micropolitical bodies, corporations, governments at local, state, and national levels as well as international organizations. In essence, actions that bolster climate resilience are ones that will enhance the adaptive capacity of social, industrial, and environmental infrastructures that can mitigate the effects of climate change. Currently, research indicates that the strongest indicator of successful climate resilience efforts at all scales is a well-developed, pre-existing network of social, political, economic and financial institutions that is already positioned to effectively take on the work of identifying and addressing the risks posed by climate change. Cities, states, and nations that have already developed such networks are, as expected, to generally have far higher net incomes and GDP.

Therefore, it can be seen that embedded within the task of building climate resilience at any scale will be the overcoming of macroscopic socioeconomic inequities: in many ways, truly facilitating the construction of climate resilient communities worldwide will require national and international agencies to address issues of global poverty, industrial development, and food justice. However, this does not mean that actions to improve climate resilience cannot be taken in real time at all levels, although evidence suggests that the most climate resilient cities and nations have accumulated this resilience through their responses to previous weather-based disasters. Perhaps even more importantly, empirical evidence suggests that the creation of the climate resilient structures is dependent upon an array of social and environmental reforms that were only successfully passed due to the presence of certain sociopolitical structures such as democracy, activist movements, and decentralization of government.

An aerial view of Delhi, India where urban forests are being developed to improve the weather resistance and climate resilience of the city

By sector

Climate resilient development

Climate resilient development has become the new paradigm for sustainable development influencing theory and practice across all sectors globally. This is particularly true in the water sector, since water security is intimately connected to climate change. On every continent, governments are adopting policies for climate resilient economies, driven in part by international frameworks such as the Paris Agreement and the Sustainable Development Goals.

Climate resilient development "integrates adaptation measures and their enabling conditions with mitigation to advance sustainable development for all". It involves questions of equity and system transitions, and includes adaptations for human, ecosystem and planetary health. Climate resilient development is facilitated by developing partnerships with traditionally marginalised groups, including women, youth, Indigenous Peoples, local communities and ethnic minorities.

To achieve climate resilient development, the following actions are needed: increasing climate information, and financing and technical capacity for flexible and dynamic systems. This needs to be coupled with greater consideration of the socio-ecological resilience and context-specific values of marginalised communities and meaningful engagement with the most vulnerable in decision making.

Climate resilient infrastructure

Infrastructure failures can have broad-reaching consequences extending away from the site of the original event, and for a considerable duration after the immediate failure. Furthermore, increasing reliance infrastructure system interdependence, in combination with the effects of climate change and population growth all contribute to increasing vulnerability and exposure, and greater probability of catastrophic failures. To reduce this vulnerability, and in recognition of limited resources and future uncertainty about climate projections, new and existing long-lasting infrastructure must undergo a risk-based engineering and economic analyses to properly allocate resources and design for climate resilience.

Incorporating climate projections into building and infrastructure design standards, investment and appraisal criteria, and model building codes is currently not common. Some resilience guidelines and risk-informed frameworks have been developed by public entities. Such manuals can offer guidance for adaptive design methods, characterization of extremes, development of flood design criteria, flood load calculation and the application of adaptive risk management principals account for more severe climate/weather extremes. One example is the "Climate Resiliency Design Guidelines" by New York City.

Climate resilient agriculture

Main articles: Effects of climate change on agriculture, Climate change adaptation § Agriculture, and Climate-smart agriculture

Multiple returns of climate resilient agriculture will be delayed. One of India's strategies, responsive crop monitoring, cannot be planned. While the government is working to create systems to guide farmers in specific situations, response farming depends on the direction of climate change. Additionally, investing in tolerant livestock breeds will decrease production in the short term. Tolerant livestock's appeal lies in their ability to resist changes to the environment as climate change worsens. These immediate uncertainties are part of India's goal of promoting environmental health to support agricultural production long term.

Similar initiatives are implemented on local scales around the world. In the United States, the state of New York's Department of Agriculture started its Climate Resilient Farming program. This program aims to reduce the impact of climate change on agriculture and mitigate agriculture's impact on climate change. It promotes similar ideas to India's, including water management and the promotion of soil health. The climate-resilient programming also provides funds to help farmers reduce methane and properly store agricultural waste. New York state's focus on reducing greenhouse gas emissions balances developing climate-resilient agriculture and the slowing of climate change.

Government support of this intersection is used to support change amongst individual farmers. As climate variability increases, the costs associated with promoting climate resilience become larger in comparison. The risk of investing in tolerant breeds, soil management, and proper environmental care can also be daunting to small farmers. Such individuals have reported hesitation to implement suggested practices like reducing herd size to promote soil-healthy grazing. The popularity of climate resilient farming amongst subsistence farmers helps ease the transition to a climate-resilient system. Alongside developing new techniques, farmers can use techniques they already knew, such as no-till farming and cover cropping.

Tools

Climate resilience framework

A climate resilience framework can better equip governments and policymakers to develop sustainable solutions that combat the effects of climate change. To begin with, climate resilience establishes the idea of multi-stable socio-ecological systems (socio-ecological systems can actually stabilize around a multitude of possible states). Secondly, climate resilience has played a critical role in emphasizing the importance of preventive action when assessing the effects of climate change. Although adaptation is always going to be a key consideration, making changes after the fact has a limited capability to help communities and nations deal with climate change. By working to build climate resilience, policymakers and governments can take a more comprehensive stance that works to mitigate the harms of climate change impacts before they happen. Finally, a climate resilience perspective encourages greater cross-scale connectedness of systems. Creating mechanisms of adaptation that occur in isolation at local, state, or national levels may leave the overall social-ecological system vulnerable. A resilience-based framework would require far more cross-talk, and the creation of environmental protections that are more holistically generated and implemented.

One weakness of centralized organisations is their lack of adaptation to climate change issues specific to territories. To overcome it, a new concept called the "mistletoe ball" society (la société "boule de gui" in French) is emerging. States can provide resources (financial, empowerment, skills) to territories so they can provide a safety net to inhabitants, companies and public organizations. In addition, each territory is linked to each other through cooperation and solidarity ties. This safety net encompasses access to energy, food, mobility, health and education, among others. It doesn't provide full services but minimum services to survive the time needed to come back to a better situation. Compared to a full autonomous territory, it brings more resilience because a territory can be overwhelmed by a natural disaster and so needs help from other areas that are not affected. In addition, it needs less resources to create a safety net rather than a full autonomous system.

Disaster preparedness protocols

Main article: Disaster risk reduction

At larger governmental levels, general programs to improve climate resiliency through greater disaster preparedness are being implemented. For example, in cases such as Norway, this includes the development of more sensitive and far-reaching early warning systems for extreme weather events, creation of emergency electricity power sources, enhanced public transportation systems, and more.

Measurements

Governments and development agencies are spending increasing amounts of finance to support resilience-building interventions. Resilience measurement can make valuable contributions in guiding resource allocations towards resilience-building. This includes targeted identification of vulnerability hotspots, a better understanding of the drivers of resilience, and tools to infer the impact and effectiveness of resilience-building interventions. In recent years, a large number of resilience measurement tools have emerged, offering ways to track and measure resilience at a range of scales - from individuals and households to communities and nations.

Efforts to measure climate resilience currently face several technical challenges. Firstly, the definition of resilience is heavily contested, making it difficult to choose appropriate characteristics and indicators to track. Secondly, the resilience or households or communities cannot be measured using a single observable metric. Resilience is made up of a range of processes and characteristics, many of which are intangible and difficult to observe (such as social capital). As a result, many resilience toolkits resort to using large lists of proxy indicators.

Most of the recent initiatives to measure resilience in rural development contexts share two shortcomings: complexity and high cost. USAID published a field guide for assessing climate resilience in smallholder supply chains.

Most objective approaches use fixed and transparent definitions of resilience and allow for different groups of people to be compared through standardized metrics. However, as many resilience processes and capacities are intangible, objective approaches are heavily reliant on crude proxies. Examples of commonly used objective measures include the Resilience Index Measurement and Analysis (RIMA) and the Livelihoods Change Over Time (LCOT).

Subjective approaches to resilience measurement take a contrasting view. They assume that people have a valid understanding of their resilience and seek to factor perceptions into the measurement process. They challenge the notion that experts are best placed to evaluate other people's lives. Subjective approaches use people's menu of what constitutes resilience and allow them to self-evaluate accordingly. An example is the Subjectively-Evaluated Resilience Score (SERS)

History

The theoretical basis for many of the ideas central to climate resilience have actually existed since the 1960s. Originally an idea defined for strictly ecological systems, resilience in ecology was initially outlined by C.S. Holling as the capacity for ecological systems and relationships within those systems to persist and absorb changes to "state variables, driving variables, and parameters." This definition helped form the foundation for the notion of ecological equilibrium: the idea that the behavior of natural ecosystems is dictated by a homeostatic drive towards some stable set point. Under this school of thought (which maintained quite a dominant status during this time period), ecosystems were perceived to respond to disturbances largely through negative feedback systems – if there is a change, the ecosystem would act to mitigate that change as much as possible and attempt to return to its prior state.

As greater amounts of scientific research in ecological adaptation and natural resource management was conducted, it became clear that oftentimes, natural systems were subjected to dynamic, transient behaviors that changed how they reacted to significant changes in state variables: rather than work back towards a predetermined equilibrium, the absorbed change was harnessed to establish a new baseline to operate under. Rather than minimize imposed changes, ecosystems could integrate and manage those changes, and use them to fuel the evolution of novel characteristics. This new perspective of resilience as a concept that inherently works synergistically with elements of uncertainty and entropy first began to facilitate changes in the field of adaptive management and environmental resources, through work whose basis was built by Holling and colleagues yet again.

By the mid 1970s, resilience began gaining momentum as an idea in anthropology, culture theory, and other social sciences. There was significant work in these relatively non-traditional fields that helped facilitate the evolution of the resilience perspective as a whole. Part of the reason resilience began moving away from an equilibrium-centric view and towards a more flexible, malleable description of social-ecological systems was due to work such as that of Andrew Vayda and Bonnie McCay in the field of social anthropology, where more modern versions of resilience were deployed to challenge traditional ideals of cultural dynamics.

Eventually by the late 1980s and early 1990s, resilience had fundamentally changed as a theoretical framework. Not only was it now applicable to social-ecological systems, but more importantly, resilience now incorporated and emphasized ideas of management, integration, and utilization of change rather than simply describing reactions to change. Resilience was no longer just about absorbing shocks, but also about harnessing the changes triggered by external stresses to catalyze the evolution the social-ecological system in question.

Examples

Improving climate resilience of water and sanitation services

Climate resilience is the ability to recover from, or to mitigate vulnerability to, climate-related shocks such as floods and droughts. Climate resilient development has become the new paradigm for sustainable development influencing theory and practice across all sectors globally. This is particularly true in the water sector, since water security is intimately connected to climate change. On every continent, governments are adopting policies for climate resilient economies. International frameworks such as the Paris Agreement and the Sustainable Development Goals are drivers for such initiatives.

Climate-resilient water services (or "climate-resilient WASH") provide access to high quality drinking water during all seasons and even during extreme weather events. The right infrastructure and management choices are important at the community and household levels in order to achieve climate resilience for water supply.

To put climate resilience into practice and to engage better with politicians, the following questions need to be addressed on a case by case basis: "resilience of what, to what, for whom, over what time frame, by whom and at what scale?":

• "Resilience of what?" means thinking beyond infrastructure but to also include resilience of water resources, local institutions and water users.
• "Resilience to what?" means that smaller variations in water quantity and quality are as important as extreme events: smaller changes in seasonal rainfall variability can have devastating impacts on rainfall-dependent communities. Moreover, those without access to safe, reliable domestic water supplies face heightened water insecurity at specific times throughout the year due to cyclical changes in water quantity or quality. For example, where access to water on-premises is not available, drinking water quality at the point of use (PoU) can be much worse compared to the quality at the point of collection (PoC). Correct household practices around hygiene, storage and treatment are therefore important. There are interactions between weather, water source and management, and these in turn impact on drinking water safety.
• "Resilience over what time frame?" refers to short term or longer-term investments.
• "Resilience for whom?" speaks about reducing vulnerability and preventing maladaptation: For instance, top-down, technocratic interventions that attempt to work around power and politics undermine indigenous knowledge and compromise community resilience.
• "Resilience by whom?" refers to the fact that including diverse actors can expose, and allow operation within, power imbalances across scales.
• And finally, "Resilience at what scale?" reminds decision makers to scale-up solutions while maintaining context specificity.

Climate change and cities

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Climate_change_and_cities 

 

Jakarta, Indonesia was listed as the most vulnerable city to climate change in a 2021 Verisk Maplecroft study.

Climate change and cities are deeply connected. Cities are one of the greatest contributors and likely best opportunities for addressing climate change. Cities are also one of the most vulnerable parts of the human society to the effects of climate change, and likely one of the most important solutions for reducing the environmental impact of humans. More than half of the world's population is in cities, consuming a large portion of food and goods produced outside of cities. The increase of urban population growth is one of the main factors in air-quality problems. In the year 2016, 31 mega-cities reported having at least 10 million in their population, 8 of which surpassed 20 million people. The UN projects that 68% of the world population will live in urban areas by 2050. Hence, cities have a significant influence on construction and transportation—two of the key contributors to global warming emissions. Moreover, because of processes that create climate conflict and climate refugees, city areas are expected to grow during the next several decades, stressing infrastructure and concentrating more impoverished peoples in cities.

Because of the high density and effects like the urban heat island affect, weather changes due to climate change are likely to greatly effect cities, exacerbating existing problems, such as air pollution, water scarcity, and heat illness in the metropolitan areas. Studies have shown that if body temperature exceeds 39°C for a period of time, serious heat stroke may occur. Some of the other extreme weather conditions caused by climate change include extreme floods, deathly snowstorms, ice storms, heat waves, droughts, and hurricanes, which are often deathly and harmful. Studies have shown that heat waves are three times more likely to occur and have become more intense since the 1960s. Moreover, because most cities have been built on rivers or coastal areas, cities are frequently vulnerable to the subsequent effects of sea level rise, which cause coastal flooding and erosion, and those effects are deeply connected with other urban environmental problems, like subsidence and aquifer depletion.

A report by the C40 Cities Climate Leadership Group described consumption based emissions as having significantly more impact than production-based emissions within cities. The report estimates that 85% of the emissions associated with goods within a city is generated outside of that city. Climate change adaptation and mitigation investments in cities will be important in reducing the impacts of some of the largest contributors of greenhouse gas emissions: for example, increased density allows for redistribution of land use for agriculture and reforestation, improving transportation efficiencies, and greening construction (largely due to cement's outsized role in climate change and improvements in sustainable construction practices and weatherization).In the most recent past, increasing urbanization has also been proposed as a phenomenon that has a reducing effect on the global rate of carbon emission primarily because with urbanization comes technical prowess which can help drive sustainability. Lists of high impact climate change solutions tend to include city-focused solutions; for example, Project Drawdown recommends several major urban investments, including improved bicycle infrastructure, building retrofitting, district heating, public transit, and walkable cities as important solutions.

Because of this, the international community has formed coalitions of cities (such as the C40 Cities Climate Leadership Group and ICLEI) and policy goals, such as Sustainable Development Goal 11 ("sustainable cities and communities"), to activate and focus attention on these solutions.

Emissions

Further information: Greenhouse gas emissions

Cities globally house half of the world's people, consume two-thirds of the world's energy and 70% of its natural resources, and contribute more than 70% of global CO₂ emissions. Cities and regions are also particularly vulnerable to climate-related hazards and pollution. Climate danger and pollution also disproportionately affect the poor, increasing inequality. With half of the world population residing in urban areas, there will be an increase in energy usage that comes with Climate Change. One of these will be AC, since climate change comes with higher temperatures many people will start needed more cooling systems, so this results in more air conditioning and newer models of cooling systems. Although more people are living in cities which can result in shortages, cities actually emit less carbon than rural areas since house sizes are smaller, more gas heat over propane is used, less carbon fueled transportation is used, and more people share communal spaces such as laundry rooms and kitchens. While cities create some problems, it is important to realize that the denser population creates less carbon emissions which benefits climate change.

With regard to methods of emissions counting cities can be challenging as production of goods and services within their territory can be related either to domestic consumption or exports. Conversely the citizens also consume imported goods and services. To avoid double counting in any emissions calculation it should be made clear where the emissions are to be counted: at the site of production or consumption. This may be complicated given long production chains in a globalized economy. Moreover, the embodied energy and consequences of large-scale raw material extraction required for renewable energy systems and electric vehicle batteries is likely to represent its own complications – local emissions at the site of utilization are likely to be very small but life-cycle emissions can still be significant.

Field of study

The research perspective of cities and climate change, started in the 1990s as the international community became increasingly aware of the potential impacts of climate change. Urban studies scholars Michael Hebbert and Vladmir Jankovic argue that this field of research grew out of a larger body of research on the effects of urban development and living on the environment starting as early as the 1950s. Since then, research has indicated relationships between climate change and sustainable urbanization: increase employment cities reduces poverty and increases efficiencies.

Two international assessments have been published by the Urban Climate Change Research Network at The Earth Institute at Columbia University. The first of which was published in, the first of which (ARC3.1) was published in 2011, and the second of which (ARC3.2) was published in 2018. These papers act as summaries of the scholarship for the field similar to the Intergovernmental Panel on Climate Change reports. A third report is being developed as of 2020.

Cities as laboratories

Cities are good subjects for study because they can invest heavily in large-scale experimental policies that could be scaled elsewhere (such as San Diego's advanced urban planning practices which could be applied elsewhere in the United States). Multiple scholars approach this in different ways, but describe this "urban laboratory" environment for testing a wide variety of practices. for example the book Life After Carbon documents a number of cities which act as "urban climate innovation laboratories". These cities as laboratories offer an efficient way to detect climate change by looking at the effects of the greenhouse effect on rooftops, street trees, and other environmental variables within a city setting. Though this method of looking at the heat waves effects in cities, it will offer a way of seeing the problem of the effect of heat that will be solved by cities within the future.

Health impacts

Climate change has been observed to have caused impact on human health and livelihoods in urban settings. Urbanization commonly occurs in cities with low and middle income communities that have high population density and a lack of understanding of how climate change, which degrades their environment, is affecting their health. Within urban settings, multiple climate and non-climate hazards impact cities which magnify the damages done to human health. For example, heatwaves have intensified in cities due to the combination of multiple factors adding to climate change. With heatwaves constantly increasing temperatures in cities, it has caused many illnesses such as heat stroke or heat cramps. The rise of temperatures due to climate change have also changed the distribution of diseases from mosquitoes, causing a rising rate of infectious diseases.  Alongside infectious diseases and heatwaves, climate change can create natural hazards such as floods, droughts, and storms due to rising sea levels. It also harms those even more who have COVID-19, asthma, illnesses, etc. The impacts on human health in urban settings is more profound in economically and socially marginalized urban residents.

Urban resilience

Further information: Climate resilience

The Intergovernmental Panel on Climate Change (IPCC) defines resilience as “the ability of a social or ecological system to absorb disturbances while retaining the same basic structure and ways of functioning, the capacity of self-organization, and the capacity to adapt to stress and change.” One of the most important notions emphasized in urban resiliency theory is the need for urban systems to increase their capacity to absorb environmental disturbances. By focusing on three generalizable elements of the resiliency movement, Tyler and Moench's urban resiliency framework serves as a model that can be implemented for local planning on an international scale.

The first element of urban climate resiliency focuses on “systems’ or the physical infrastructure embedded in urban systems. A critical concern of urban resiliency is linked to the idea of maintaining support systems that in turn enable the networks of provisioning and exchange for populations in urban areas. These systems concern both physical infrastructure in the city and ecosystems within or surrounding the urban center; while working to provide essential services like food production, flood control, or runoff management. For example, city electricity, a necessity of urban life, depends on the performance of generators, grids, and distant reservoirs. The failure of these core systems jeopardizes human well-being in these urban areas, with that being said, it is crucial to maintain them in the face of impending environmental disturbances. Societies need to build resiliency into these systems in order to achieve such a feat. Resilient systems work to “ensure that functionality is retained and can be re-instated through system linkages” despite some failures or operational disturbances. Ensuring the functionality of these important systems is achieved through instilling and maintaining flexibility in the presence of a “safe failure.” Resilient systems achieve flexibility by making sure that key functions are distributed in a way that they would not all be affected by a given event at one time, what is often referred to as spatial diversity, and has multiple methods for meeting a given need, what is often referred to as functional diversity. The presence of safe failures also plays a critical role in maintaining these systems, which work by absorbing sudden shocks that may even exceed design thresholds. Environmental disturbances are certainly expected to challenge the dexterity of these systems, so the presence of safe failures almost certainly appears to be a necessity.

Many European respondents to a survey on climate believe they might have to move regions or countries because of climate change

Further, another important component of these systems is bounce-back ability. In the instance where dangerous climatic events affect these urban centers, recovering or "bouncing-back" is of great importance. In fact, in most disaster studies, urban resilience is often defined as "the capacity of a city to rebound from destruction." This idea of bounce-back for urban systems is also engrained in governmental literature of the same topic. For example, the former government's first Intelligence and Security Coordinator of the United States described urban resilience as "the capacity to absorb shocks and to bounce back into functioning shape, or at the least, sufficient resilience to prevent...system collapse." Keeping these quotations in mind, bounce-back discourse has been and should continue to be an important part of urban climate resiliency framework. Other theorists have critiqued this idea of bounce-back, citing this as privileging the status quo, rather advocating the notion of ‘bouncing forward’, permitting system evolution and improvement.

The next element of urban climate resiliency focuses on the social agents (also described as social actors) present in urban centers. Many of these agents depend on the urban centers for their very existence, so they share a common interest of working towards protecting and maintaining their urban surroundings. Agents in urban centers have the capacity to deliberate and rationally make decisions, which plays an important role in climate resiliency theory. One cannot overlook the role of local governments and community organizations, which will be forced to make key decisions with regards to organizing and delivering key services and plans for combating the impending effects of climate change. Perhaps most importantly, these social agents must increase their capacities with regards to the notions of “resourcefulness and responsiveness. Responsiveness refers to the capacity of social actors and groups to organize and re-organize, as well as the ability to anticipate and plan for disruptive events. Resourcefulness refers to the capacity of social actors in urban centers to mobilize varying assets and resources in order to take action. Urban centers will be able to better fend for themselves in the heat of climatic disturbances when responsiveness and resourcefulness is collectively achieved in an effective manner.

Regional and national differences

Cities in different parts of the world face different, unique challenges and opportunities in the face of climate change. However, one linking factor is their inevitable adherence to "Dominant global patterns of urbanization and industrialization" which often catalyzes "large-scale modification of the drivers for hydrologic and biogeochemical processes". Urbanization and industrialization patterns are particularly evident for regions such as Asia, Africa, and South America, regions that are currently understood as experiencing related rapid shifts in population and economic prowess.

Africa

Main article: Climate change in Africa

Africa is urbanizing faster than any other continent and it is estimated that by 2030, more than one billion Africans will live in cities. This rapid urbanization, coupled with the many interlinked and complex challenges as a result of climate change, pose a significant barrier to Africa's sustainable development. Much of this Urban Development is informal, with urban residents settling in informal settlements and slums often on the outskirts of cities. This phenomenon suggests that lower-income countries should be targeted in initiatives to increase infrastructural sustainability. A recent study found that in "countries with per capita incomes of below USD 15,000 per year (at PPP-adjusted 2011 USD) carbon pricing has, on average, progressive distributional effects" and that "carbon pricing tends to be regressive in countries with relatively higher income," indicating that carbon taxing and shifting carbon prices might incentivize governments to shift to green energy as the baseline energy consumption method for developing peri-urban areas. Although urbanization is seen in a positive light, the effects of it can be negative on those being urbanized. African cities are exposed to multiple climate threats including floods, drought, water stress, sea level rise, heat waves, storms and cyclones, and the related effects of food insecurity and disease outbreaks like Cholera and Malaria from floods and droughts.

Climate impacts in rural areas, such as desertification, biodiversity loss, soil erosion and declines in agricultural productivity, are also driving rural-urban migration of poor rural communities to cities. To achieve sustainable development and climate resilience in cities in Africa, and elsewhere, it is important to consider these urban-rural interlinkages. Increasing attention is being paid to the important role of peri-urban areas in urban climate resilience, particularly regarding the ecosystem services that these areas provide and which are rapidly deteriorating in Sub-Saharan Africa. Peri-urban ecosystems can provide functions such as controlling floods, reducing the urban heat island effect, purifying air and water, supporting food and water security, and managing waste.

Asia

China

Main article: climate change in China

China currently has one of the fastest-growing industrial economies in the world, and the effects of this rapid urbanization have not been without climate change implications. The country is one of the largest by land area, and so the most prominent region regarding urbanization is the Yangtze River Delta, or YRD, as it is considered "China's most developed, dynamic, densely populated and concentrated industrial area" and is allegedly "growing into an influential world-class metropolitan area and playing an important role in China’s economic and social development". In this way urbanization in China could be understood as intimately related to not only the functionality of their economic system, but the society therein; something that makes climate change mitigation an intersectional issue concerning more than simply infrastructure.

The data show that "High-administrative-level cities had stronger adaptation, lower vulnerability, and higher readiness than ordinary prefecture-level cities."China's large-scale population migration to the Yangtze River Delta and agglomeration due to rapid urbanization. Blind expansion in the construction of eastern coastal cities due to population pressure is even more unfavorable for urban climate governance.

Historically, data has shown that "climate change has been shaping the Delta and its socio-economic development" and that such socio-economic development in the region "has shaped its geography and built environment, which, however, are not adaptable to future climate change". Thus, it has been stated that "It is imperative to adopt policies and programs to mitigate and adapt to climate change" in the YRD, specifically, policies that are aimed at reducing the impact of particular climate threats based on the YRD's geography. This includes the region's current infrastructure in the mitigation of flood disasters and promotion of efficient energy usage at the local level.

A national-level policy analysis done on the drylands of northern China presents the notion of "sustainable urban landscape planning (SULP)" that specifically aims to "avoid occupying important natural habitats and corridors, prime croplands, and floodplains". The research indicates that adopting SULPs moving into the future can "effectively manage the impacts of climate change on water resource capacity and reduce water stress" not only within the northern China experimental model but for "drylands around the world".

South Asia

Main article: Climate change in South Asia

South Asia's urban population grew by 130 million between 2001 and 2011—more than the entire population of Japan—and is poised to rise by almost 250 million by 2030. But, urbanisation in South Asia is characterized by higher poverty, slums, pollution and crowding and congestion. At least 130 million South Asians—more than the entire population of Mexico—live in informal urban settlements characterized by poor construction, insecure tenure and underserviced plots. Despite being a water-rich zone, climate projection models suggest that by 2050, between 52 and 146 million people living in South Asia could face increased water scarcity due to climate change, accounting for 18% of the global population exposed to water scarcity. Urban water access is particularly critical in South Asia as it remains home to more than 40% of the world's poor (living on less than US$1.25 per day) and 35% of the world's undernourished. A study done of selected Himalayan cities in India and Nepal found that none of them have a robust system of water planning and governance to tackle the water challenges emerging from rapid urbanization and climate change. Khulna, Bangladesh is also facing many issues surrounding water insecurity as well. As sea levels begin to rise, due to climate change, salinity will move inwards, reducing the amount of safe drinking water available to the people of Khulna. There are plans being put in place to make the quality of water in cities better, but this decreases the availability to those in the informal urban areas. As of now they rely on using on as little water as possible, specifically for their crops.

North and South America

Brazil

Main article: Climate change in Brazil

Areas of South America were also cited in recent studies that highlight the dangers of urbanization on both local and transnational climates, and for a country like Brazil, one of the highest populated nations in the world as well as the majority holder of the Amazon rainforest. The United Nations Development Programme highlights the Amazon rainforest as serving a "key function in the global climate systems," granted its profound usefulness in capturing CO₂ emissions. UN research has indicated that because of Brazil's climate being so intimately reliant on the health of the rainforest, deforestation measures are currently seen as having adverse effects on the rainforest's "natural adaptive capacities" towards extreme climate shifts, thus predisposing Brazil to what are expected to be increased volatility in temperature and rainfall patterns. More specifically, it is expected that if global warming continues on its current path without vast mitigation strategies being put in place, what is currently predicted to be an average 2 °C increase in temperature at the global scale could look like a 4 °C within Brazil and the surrounding Amazon region. Rapid urbanization in other countries will also result in higher need for resources. This includes resources that will cause further deforestation of the Amazon Rainforest to obtain. This will inevitably create a lot more Climate issues, as we continue to lose more trees in the Amazon rainforest.

Issues of climate change in Brazil do not start and end at what has already been done with regards to urbanization; it is very much an issue rooted in socioeconomic contexts. Factor analysis and multilevel regression models sponsored by the U.S. Forest Service revealed that for all of Brazil, "income inequality significantly predicts higher levels of a key component of vulnerability in urban Brazilian municipalities" to flood hazards.

The future of Brazil's effect of climate is likely to change since though its NDC Brazil has made the commitment to lower their Greenhouse gas emissions by 37% below their 2005 levels by 2025. This will likely serve as a challenge within the cities of Brazil since 86% of the whole countries population lives in the urban areas, and this is likely to increase to 92% by 2050. As for deforestation, since Brazil is home to the Amazon rainforest, Brazil has always had a high deforestation rate. Brazils deforestation was at a high in 2004 with having 27.77 thousand kilometers of forest being destroyed, having a low in 2012 with only 4.57 thousand kilometers of forest being destroyed, and since then it has been back on the incline with 10.85 thousand kilometers of forest being destroyed.

United States

Main article: Climate change in the United States

The United States, as one of the largest industrialized nations in the world, also has issues regarding infrastructural insufficiencies linked to climate change. Take a study of Las Vegas topology as an indicator. Research that created three Land use/land cover maps, or LULC maps, of Las Vegas in 1900 (albeit hypothetical), 1992, and 2006 found that "urbanization in Las Vegas produces a classic urban heat island (UHI) at night but a minor cooling trend during the day". In addition to temperature changes in the city, "increased surface roughness" caused by the addition of skyscrapers/closely packed buildings in its own way were found "to have a mechanical effect of slowing down the climatological wind Windfield over the urban area". Cities in the United States that are heavily industrialized, such as Los Angeles, are responsible for a large number of greenhouse emissions due to the amount of transportation needed for millions of people living in one city. Such unnatural environmental phenomena furthers the notion that urbanization has a role in determining local climate, although researchers acknowledge that more studies need to be conducted in the field.

Cities play an important role in investing in climate innovation in the United States. Often local climate policies in cities, preempt larger policies pursued by the states or federal government. For example, following the United States withdrawal from the Paris Agreement a coalition of cities, under the banner of Mayors National Climate Action Agenda. A 2020 study of US cities found that 45 of the 100 largest cities in the U.S. had made commitments by 2017, which led to a reduction of 6% of U.S. emissions by 2020.

Clean Air Act

Since the Clean Air Act's passing in 1963 as a landmark piece of legislation aimed at controlling air quality at the national level, research has indicated that "the mean wet deposition flux... has decreased in the U.S. over time" since its enactment. Even then, however, the same research indicated that measurements in the amounts of chemical pollutants contaminating rain, snow, and fog "follows an exponential probability density function at all sites". Such a finding suggests that alleged variability in rainfall patterns is the likely driving factor for the study's seemingly promising results, as opposed to there being a clear significance stemming from the policy change. It is within this context that while beneficial, the Clean Air Act alone cannot stand as the only firm rationale for climate policies in the United States moving forward.

Mayors National Climate Action Agenda

Mayors National Climate Action Agenda, or Climate Mayors, is an association of United States mayors with the stated goal of reducing greenhouse gas emissions. Founded by Los Angeles mayor Eric Garcetti, former Houston mayor Annise Parker, and former Philadelphia mayor Michael Nutter, the group represents 435 cities and nearly 20% of the U.S. population.

Founded in 2014, the organization received one million dollars in start-up funding from the Clinton Global Initiative to support the founding mayors' efforts to organize cities in advance of the signing of the 2015 Paris Agreement.

The organization has stated its commitment to upholding the emissions goals of the Paris Agreement on climate change even if the United States withdraws from the agreement.

International policy

Several major international communities of cities and policies have been formed to include more cities in climate action.

C40

The C40 Cities Climate Leadership Group is a group of 97 cities around the world that represents one twelfth of the world's population and one quarter of the global economy. Created and led by cities, C40 is focused on fighting climate change and driving urban action that reduces greenhouse gas emissions and climate risks, while increasing the health, wellbeing and economic opportunities of urban citizens.

From 2021, Mayor of London, Sadiq Khan, serves as the C40's chairperson, former mayor of New York City Michael Bloomberg as president of the board, and Mark Watts as executive director. All three work closely with the 13-member steering committee, the board of directors and professional staff. The rotating steering committee of C40 mayors provides strategic direction and governance. Steering committee members include: Accra, Bogota, Boston, Buenos Aires, Copenhagen, Dhaka, Dubai, Durban, Hong Kong, London, Los Angeles, Milan, Seattle, and Stockholm.

Working across multiple sectors and initiative areas, C40 convenes networks of cities providing a suite of services in support of their efforts, including: direct technical assistance; facilitation of peer-to-peer exchange; and research, knowledge management & communications. C40 is also positioning cities as a leading force for climate action around the world, defining and amplifying their call to national governments for greater support and autonomy in creating a sustainable future.

SDG 11: Sustainable cities and communities

Sustainable Development Goal 11 (SDG 11 or Global Goal 11), titled "sustainable cities and communities", is one of 17 Sustainable Development Goals established by the United Nations General Assembly in 2015. The official mission of SDG 11 is to "Make cities inclusive, safe, resilient and sustainable". The 17 SDGs take into account that action in one area will affect outcomes in other areas as well, and that development must balance social, economic and environmental sustainability.

SDG 11 has 10 targets to be achieved, and this is being measured with 15 indicators. The seven "outcome targets" include safe and affordable housing, affordable and sustainable transport systems, inclusive and sustainable urbanization, protection of the world's cultural and natural heritage, reduction of the adverse effects of natural disasters, reduction of the environmental impacts of cities and to provide access to safe and inclusive green and public spaces. The three "means of achieving" targets include strong national and regional development planning, implementing policies for inclusion, resource efficiency, and disaster risk reduction in supporting the least developed countries in sustainable and resilient building. 3.9 billion people—half of the world’s population—currently live in cities globally. It is projected that 5 billion people will live in cities by 2030. Cities across the world occupy just 3 percent of the Earth's land, yet account for 60–80 percent of energy consumption and 75 percent of carbon emissions. Increased urbanization requires increased and improved access to basic resources such as food, energy and water. In addition, basic services such as sanitation, health, education, mobility and information are needed. However, these requirements are unmet globally, which causes serious challenges for the viability and safety of cities to meet increased future demands.

SDG 11 represents a shift in international development cooperation from a focus on poverty as a rural phenomenon to recognizing that cities, especially in the global south, are facing major challenges with extreme poverty, environmental degradation and risks due to climate change and natural disasters. Despite its ambiguous targets and goals, is still an important tool for addressing urban challenges and calls for actors to develop realistic, locally defined indicators and outputs to fit the urban context of specific cities to promote more sustainable, inclusive and equal cities.

Global Covenant of Mayors for Climate and Energy

The Global Covenant of Mayors for Climate & Energy was established in 2016 by bringing formally together the Compact of Mayors and the European Union's Covenant of Mayors. It is a global coalition of city leaders addressing climate change by pledging to cut greenhouse gas emissions and prepare for the future impacts of climate change. The Compact highlights cities' climate impact while measuring their relative risk levels and carbon pollution. The Compact of Mayors seeks to show the importance of city climate action, both at the local level and around the world. The Compact was launched in 2014 by UN Secretary General Ban Ki-moon and former New York City Mayor Michael Bloomberg, the UN Special Envoy for Cities and Climate Change. The Compact represents a common effort from global city networks C40 Cities Climate Leadership Group (C40), ICLEI, and United Cities and Local Governments (UCLG), as well as UN-Habitat, to unite against climate change. 428 global cities have committed to the Compact of Mayors. The collective member cities comprise over 376 million people and 5.19% of the global population.

Hypoxia (medical)

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Hypoxia_(medical) 

 

Hypoxia
Other names	Hypoxiation, lack of, low blood oxygen, oxygen starvation
Cyanosis of the hand in an elderly person with low oxygen saturation
Specialty	Pulmonology, toxicology
Symptoms	Cyanosis, numbness or pins and needles feeling of the extremities
Complications	Gangrene, necrosis
Risk factors	Diabetes, coronary artery disease, heart attack, stroke, embolism, thrombosis, deep-vein thrombosis, tobacco smoking

Hypoxia is a condition in which the body or a region of the body is deprived of adequate oxygen supply at the tissue level. Hypoxia may be classified as either generalized, affecting the whole body, or local, affecting a region of the body. Although hypoxia is often a pathological condition, variations in arterial oxygen concentrations can be part of the normal physiology, for example, during hypoventilation training or strenuous physical exercise.

Hypoxia differs from hypoxemia and anoxemia in that hypoxia refers to a state in which oxygen supply is insufficient, whereas hypoxemia and anoxemia refer specifically to states that have low or zero arterial oxygen supply. Hypoxia in which there is complete deprivation of oxygen supply is referred to as anoxia.

Generalized hypoxia occurs in healthy people when they ascend to high altitude, where it causes altitude sickness leading to potentially fatal complications: high altitude pulmonary edema (HAPE) and high altitude cerebral edema (HACE). Hypoxia also occurs in healthy individuals when breathing mixtures of gases with a low oxygen content, e.g. while diving underwater especially when using closed-circuit rebreather systems that control the amount of oxygen in the supplied air. Mild, non-damaging intermittent hypoxia is used intentionally during altitude training to develop an athletic performance adaptation at both the systemic and cellular level.

In acute or silent hypoxia, a person's oxygen level in blood cells and tissue can drop without any initial warning, even though the individual's chest x-ray shows diffuse pneumonia with an oxygen level below normal. Doctors report cases of silent hypoxia with COVID-19 patients who did not experience shortness of breath or coughing until their oxygen levels had plummeted to such a degree that the patients risked acute respiratory distress (ARDS) and organ failure. In a New York Times opinion piece (April 20, 2020), emergency room doctor Richard Levitan reports: "A vast majority of Covid pneumonia patients I met had remarkably low oxygen saturations at triage—seemingly incompatible with life—but they were using their cellphones as we put them on monitors."

Hypoxia is a common complication of preterm birth in newborn infants. Because the lungs develop late in pregnancy, premature infants frequently possess underdeveloped lungs. To improve lung function, doctors frequently place infants at risk of hypoxia inside incubators (also known as humidicribs) that provide warmth, humidity, and oxygen. More serious cases are treated with CPAP.

The 2019 Nobel Prize in Physiology or Medicine was awarded to William G. Kaelin Jr., Sir Peter J. Ratcliffe, and Gregg L. Semenza in recognition of their discovery of cellular mechanisms to sense and adapt to different oxygen concentrations, establishing a basis for how oxygen levels affect physiological function.

Generalized hypoxia

The symptoms of generalized hypoxia depend on its severity and acceleration of onset. In the case of altitude sickness, where hypoxia develops gradually, the symptoms include fatigue, numbness / tingling of extremities, nausea, and cerebral anoxia. These symptoms are often difficult to identify, but early detection of symptoms can be critical.

In severe hypoxia, or hypoxia of very rapid onset, ataxia, confusion, disorientation, hallucinations, behavioral change, severe headaches, reduced level of consciousness, papilloedema, breathlessness, pallor, tachycardia, and pulmonary hypertension eventually leading to the late signs cyanosis, slow heart rate, cor pulmonale, and low blood pressure followed by heart failure eventually leading to shock and death.

Because hemoglobin is a darker red when it is not bound to oxygen (deoxyhemoglobin), as opposed to the rich red color that it has when bound to oxygen (oxyhemoglobin), when seen through the skin it has an increased tendency to reflect blue light back to the eye. In cases where the oxygen is displaced by another molecule, such as carbon monoxide, the skin may appear 'cherry red' instead of cyanotic. Hypoxia can cause premature birth, and injure the liver, among other deleterious effects.

Local hypoxia

If tissue is not being perfused properly, it may feel cold and appear pale; if severe, hypoxia can result in cyanosis, a blue discoloration of the skin. If hypoxia is very severe, a tissue may eventually become gangrenous. Extreme pain may also be felt at or around the site.

Tissue hypoxia from low oxygen delivery may be due to low haemoglobin concentration (anaemic hypoxia), low cardiac output (stagnant hypoxia) or low haemoglobin saturation (hypoxic hypoxia). The consequence of oxygen deprivation in tissues is a switch to anaerobic metabolism at the cellular level. As such, reduced systemic blood flow may result in increased serum lactate. Serum lactate levels have been correlated with illness severity and mortality in critically ill adults and in ventilated neonates with respiratory distress.

Cause

Oxygen passively diffuses in the lung alveoli according to a pressure gradient. Oxygen diffuses from the breathed air, mixed with water vapour, to arterial blood, where its partial pressure is around 100 mmHg (13.3 kPa). In the blood, oxygen is bound to hemoglobin, a protein in red blood cells. The binding capacity of hemoglobin is influenced by the partial pressure of oxygen in the environment, as described in the oxygen–hemoglobin dissociation curve. A smaller amount of oxygen is transported in solution in the blood.

In peripheral tissues, oxygen again diffuses down a pressure gradient into cells and their mitochondria, where it is used to produce energy in conjunction with the breakdown of glucose, fats, and some amino acids. Hypoxia can result from a failure at any stage in the delivery of oxygen to cells. This can include decreased partial pressures of oxygen, problems with diffusion of oxygen in the lungs, insufficient available hemoglobin, problems with blood flow to the end tissue, and problems with breathing rhythm. Experimentally, oxygen diffusion becomes rate limiting (and lethal) when arterial oxygen partial pressure falls to 60 mmHg (5.3 kPa) or below.

Almost all the oxygen in the blood is bound to hemoglobin, so interfering with this carrier molecule limits oxygen delivery to the periphery. Hemoglobin increases the oxygen-carrying capacity of blood by about 40-fold, with the ability of hemoglobin to carry oxygen influenced by the partial pressure of oxygen in the environment, a relationship described in the oxygen–hemoglobin dissociation curve. When the ability of hemoglobin to carry oxygen is interfered with, a hypoxic state can result.

Ischemia

Main article: Ischemia

Ischemia, meaning insufficient blood flow to a tissue, can also result in hypoxia. This is called 'ischemic hypoxia'. This can include an embolic event, a heart attack that decreases overall blood flow, or trauma to a tissue that results in damage. An example of insufficient blood flow causing local hypoxia is gangrene that occurs in diabetes.

Diseases such as peripheral vascular disease can also result in local hypoxia. For this reason, symptoms are worse when a limb is used. Pain may also be felt as a result of increased hydrogen ions leading to a decrease in blood pH (acidity) created as a result of anaerobic metabolism.

Hypoxemic hypoxia

Main article: Hypoxemia

This refers specifically to hypoxic states where the arterial content of oxygen is insufficient. This can be caused by alterations in respiratory drive, such as in respiratory alkalosis, physiological or pathological shunting of blood, diseases interfering in lung function resulting in a ventilation-perfusion mismatch, such as a pulmonary embolus, or alterations in the partial pressure of oxygen in the environment or lung alveoli, such as may occur at altitude or when diving.

Carbon monoxide poisoning

Main article: Carbon monoxide poisoning

Carbon monoxide competes with oxygen for binding sites on hemoglobin molecules. As carbon monoxide binds with hemoglobin hundreds of times tighter than oxygen, it can prevent the carriage of oxygen. Carbon monoxide poisoning can occur acutely, as with smoke intoxication, or over a period of time, as with cigarette smoking. Due to physiological processes, carbon monoxide is maintained at a resting level of 4–6 ppm. This is increased in urban areas (7–13 ppm) and in smokers (20–40 ppm). A carbon monoxide level of 40 ppm is equivalent to a reduction in hemoglobin levels of 10 g/L.

CO has a second toxic effect, namely removing the allosteric shift of the oxygen dissociation curve and shifting the foot of the curve to the left. In so doing, the hemoglobin is less likely to release its oxygens at the peripheral tissues. Certain abnormal hemoglobin variants also have higher than normal affinity for oxygen, and so are also poor at delivering oxygen to the periphery.

Altitude

Main article: Altitude sickness

Atmospheric pressure reduces with altitude and with it, the amount of oxygen. The reduction in the partial pressure of inspired oxygen at higher altitudes lowers the oxygen saturation of the blood, ultimately leading to hypoxia. The clinical features of altitude sickness include: sleep problems, dizziness, headache and oedema.

Hypoxic breathing gases

Main articles: Inert gas asphyxiation and Asphyxiant gases

The breathing gas in underwater diving may contain an insufficient partial pressure of oxygen, particularly in malfunction of rebreathers. Such situations may lead to unconsciousness without symptoms since carbon dioxide levels are normal and the human body senses pure hypoxia poorly. Hypoxic breathing gases can be defined as mixtures with a lower oxygen fraction than air, though gases containing sufficient oxygen to reliably maintain consciousness at normal sea level atmospheric pressure may be described as normoxic even when slightly hypoxic. Hypoxic mixtures in this context are those which will not reliably maintain consciousness at sea level pressure. Gases with as little as 2% oxygen by volume in a helium diluent are used for deep diving operations. The ambient pressure at 190 msw is sufficient to provide a partial pressure of about 0.4 bar, which is suitable for saturation diving. As the divers are decompressed, the breathing gas must be oxygenated to maintain a breathable atmosphere.

Inert gas asphyxiation may be deliberate with use of a suicide bag. Accidental death has occurred in cases where concentrations of nitrogen in controlled atmospheres, or methane in mines, has not been detected or appreciated.

Other

Hemoglobin's function can also be lost by chemically oxidizing its iron atom to its ferric form. This form of inactive hemoglobin is called methemoglobin and can be made by ingesting sodium nitrite as well as certain drugs and other chemicals.

Anemia

Main article: Anemia

Hemoglobin plays a substantial role in carrying oxygen throughout the body, and when it is deficient, anemia can result, causing 'anaemic hypoxia' if tissue perfusion is decreased. Iron deficiency is the most common cause of anemia. As iron is used in the synthesis of hemoglobin, less hemoglobin will be synthesised when there is less iron, due to insufficient intake, or poor absorption.

Anemia is typically a chronic process that is compensated over time by increased levels of red blood cells via upregulated erythropoetin. A chronic hypoxic state can result from a poorly compensated anaemia.

Histotoxic hypoxia

Main article: Histotoxic hypoxia

Cyanide poisoning

Histotoxic hypoxia results when the quantity of oxygen reaching the cells is normal, but the cells are unable to use the oxygen effectively as a result of disabled oxidative phosphorylation enzymes. This may occur in cyanide poisoning.

Physiological compensation

Acute

If oxygen delivery to cells is insufficient for the demand (hypoxia), electrons will be shifted to pyruvic acid in the process of lactic acid fermentation. This temporary measure (anaerobic metabolism) allows small amounts of energy to be released. Lactic acid build up (in tissues and blood) is a sign of inadequate mitochondrial oxygenation, which may be due to hypoxemia, poor blood flow (e.g., shock) or a combination of both. If severe or prolonged it could lead to cell death.

In humans, hypoxia is detected by the peripheral chemoreceptors in the carotid body and aortic body, with the carotid body chemoreceptors being the major mediators of reflex responses to hypoxia. This response does not control ventilation rate at normal pO
₂, but below normal the activity of neurons innervating these receptors increases dramatically, so much so to override the signals from central chemoreceptors in the hypothalamus, increasing pO
₂ despite a falling pCO₂

In most tissues of the body, the response to hypoxia is vasodilation. By widening the blood vessels, the tissue allows greater perfusion.

By contrast, in the lungs, the response to hypoxia is vasoconstriction. This is known as hypoxic pulmonary vasoconstriction, or "HPV".

Chronic

When the pulmonary capillary pressure remains elevated chronically (for at least 2 weeks), the lungs become even more resistant to pulmonary edema because the lymph vessels expand greatly, increasing their capability of carrying fluid away from the interstitial spaces perhaps as much as 10-fold. Therefore, in patients with chronic mitral stenosis, pulmonary capillary pressures of 40 to 45 mm Hg have been measured without the development of lethal pulmonary edema.[Guytun and Hall physiology]

Hypoxia exists when there is a reduced amount of oxygen in the tissues of the body. Hypoxemia refers to a reduction in PO2 below the normal range, regardless of whether gas exchange is impaired in the lung, CaO2 is adequate, or tissue hypoxia exists. There are several potential physiologic mechanisms for hypoxemia, but in patients with COPD the predominant one is V/Q mismatching, with or without alveolar hypoventilation, as indicated by PaCO2. Hypoxemia caused by V/Q mismatching as seen in COPD is relatively easy to correct, so that only comparatively small amounts of supplemental oxygen (less than 3 L/min for the majority of patients) are required for LTOT. Although hypoxemia normally stimulates ventilation and produces dyspnea, these phenomena and the other symptoms and signs of hypoxia are sufficiently variable in patients with COPD as to be of limited value in patient assessment. Chronic alveolar hypoxia is the main factor leading to development of cor pulmonale—right ventricular hypertrophy with or without overt right ventricular failure—in patients with COPD. Pulmonary hypertension adversely affects survival in COPD, to an extent that parallels the degree to which resting mean pulmonary artery pressure is elevated. Although the severity of airflow obstruction as measured by FEV1 is the best correlate with overall prognosis in patients with COPD, chronic hypoxemia increases mortality and morbidity for any severity of disease. Large-scale studies of LTOT in patients with COPD have demonstrated a dose–response relationship between daily hours of oxygen use and survival. There is reason to believe that continuous, 24-hours-per-day oxygen use in appropriately selected patients would produce a survival benefit even greater than that shown in the NOTT and MRC studies.

Treatment

To counter the effects of high-altitude diseases, the body must return arterial pO
₂ toward normal. Acclimatization, the means by which the body adapts to higher altitudes, only partially restores pO
₂ to standard levels. Hyperventilation, the body's most common response to high-altitude conditions, increases alveolar pO
₂ by raising the depth and rate of breathing. However, while pO
₂ does improve with hyperventilation, it does not return to normal. Studies of miners and astronomers working at 3000 meters and above show improved alveolar pO
₂ with full acclimatization, yet the pO
₂ level remains equal to or even below the threshold for continuous oxygen therapy for patients with chronic obstructive pulmonary disease (COPD). In addition, there are complications involved with acclimatization. Polycythemia, in which the body increases the number of red blood cells in circulation, thickens the blood, raising the danger that the heart can't pump it.

In high-altitude conditions, only oxygen enrichment can counteract the effects of hypoxia. By increasing the concentration of oxygen in the air, the effects of lower barometric pressure are countered and the level of arterial pO
₂ is restored toward normal capacity. A small amount of supplemental oxygen reduces the equivalent altitude in climate-controlled rooms. At 4000 m, raising the oxygen concentration level by 5 percent via an oxygen concentrator and an existing ventilation system provides an altitude equivalent of 3000 m, which is much more tolerable for the increasing number of low-landers who work in high altitude. In a study of astronomers working in Chile at 5050 m, oxygen concentrators increased the level of oxygen concentration by almost 30 percent (that is, from 21 percent to 27 percent). This resulted in increased worker productivity, less fatigue, and improved sleep.

Oxygen concentrators are uniquely suited for this purpose. They require little maintenance and electricity, provide a constant source of oxygen, and eliminate the expensive, and often dangerous, task of transporting oxygen cylinders to remote areas. Offices and housing already have climate-controlled rooms, in which temperature and humidity are kept at a constant level.

A prescription renewal for home oxygen following hospitalization requires an assessment of the patient for ongoing hypoxemia.