This background justifies using the human life

 

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 When ice melts, less radiated heat from the sun is reflected back into space, so more is absorbed, causing more ice to melt (Albedo).

2. As the carbon content of oceans and soils increases, their ability to absorb CO₂ falls (Gattuso et al., 2015).

3. When permafrost (tundra) peat thaws, it releases CO₂, methane (CH₄), and nitrous oxide (N₂O), causing more warming and melting (Voigt et al., 2017). Permafrost peat contains about 1,700 Pg carbon—about twice as much as the entire atmosphere—of which 30% (68–508 Pg) could be released by 2100 (MacDougall et al., 2012). Atmospheric CH₄ concentration has unexpectedly accelerated in recent years (Nisbet et al., 2018).

4. Forests will dry out at the same time as weather conditions that cause fires (dry soil, high temperature, low humidity, and high winds) become more frequent. Fires produce CO₂, causing more warming and drying (Gabbert, 2018; Reidmiller, 2018). Forest dieback can be caused by a combination of drought and bark-beetle infestation, caused in turn by AGW (Sangüesa-Barreda et al., 2015). Beetle-caused dieback can switch a forest from a carbon sink to a carbon source (Hansen et al., 2013a). Between 1984 and 2016, the European forest area affected by mortality doubled—largely due to AGW and land-use changes (Senf et al., 2018).

5. Extreme temperatures caused by climate change will increase human energy consumption for heating and cooling (International Energy Agency, 2019).

When feedbacks are taken into account, the global carbon budget for limiting AGW to 2 or 1.5°C is reduced by “several years of anthropogenic carbon dioxide emissions at present rates” (Lowe and Bernie, 2018, abstract).

The Human Life as a Unit of Value

Consider the following two theses: (1) human lives are equal in value and (2) human lives are the most valuable thing that humans know. Scientific research is consistent with (1), having failed to find evidence for inherent biological or cultural differences in value or ability (e.g., intelligence) between human groups (Fairchild, 1991). Consistent with both points, Kant (1785/2011) proposed a “kingdom of ends,” in which people are always considered as ends and never as means, implying that their value is incomparable with other forms of value.

The two theses have a strong legal foundation. The Universal Declaration of Human Rights, adopted by the United Nations in 1948, repeatedly refers to human equality. The first sentence of the declaration specifies “the inherent dignity and of the equal and inalienable rights of all members of the human family.” The preamble also mentions the “equal rights of men and women.” Article 1 proclaims that “All human beings are born free and equal in dignity and rights.” Article 7 adds that “All are equal before the law and are entitled without any discrimination to equal protection of the law.” According to Article 10, “Everyone is entitled in full equality to a fair and public hearing by an independent and impartial tribunal.” The principle of equality also applies to marriage (Article 16), access to public service and voting rights (21), pay for work (23), and access to education (26).

This background justifies using the human life as a unit for measuring the size of a disaster or catastrophe—comparable with kilograms, meters, and seconds for physical measurements. The number of deaths associated with a given event is an objective (although approximate) measure of the suffering associated with that event, and hence with its magnitude or seriousness.

Subjective estimates are different. First, the perceived size of a number is not proportional to its actual size: “one billion” does not seem a thousand times bigger than “one million”. Second, psychic numbing (Lifton, 1982) means a large disaster may not seem bigger or more important than a small one. Neuroscientific evidence (Dehaene, 2003) points to an approximately logarithmic relationship between the number of deaths and the perceived magnitude of a disaster.

A scientifically founded humanitarian approach should aspire to overcome such subjective limitations. “This perspective presumes a linear relationship between the number of lives one can save in a given situation and the value associated with saving them. Thus an effort saving 200 lives would have twice the value of another that saves 100 lives” (Fetherstonhaugh et al., 1997, p. 285).

Estimating Future Death Tolls

Future death tolls in connection with AGW will depend on climate in various ways. Changes in extreme temperatures (lows in winter and highs in summer) at a given location are one of many possible climate-related causes of death; studies that focus on this aspect (e.g., Kalkstein and Greene, 1997; Nicholls, 2009; Huber et al., 2017) may be ignoring the main drivers. Death rates will be highest in developing countries or among people living in poverty, so studies with that focus are more relevant.

AGW interacts in complex ways with several of the Sustainable Development Goals (Nilsson et al., 2016). Many different climate impacts could directly or indirectly lead to premature death or exacerbate existing rates of premature death from hunger or avoidable disease. Vector- and rodent-borne diseases including arboviral (dengue, chikungunya, West Nile, and malaria) may change their geographic distribution with climate change (temperature, extreme weather events, and seasonality) and environmental factors (land-use, ecosystems, deforestation, hydrology, and biodiversity); rodent population density and distribution are also affected by weather conditions (Apfel, 2007, p. 4). “(H)uman illnesses due to antimicrobial-resistant infections may become a major cause of death from infectious diseases worldwide by 2050” (UN Environment, 2019, p. 12). At the same time, food demands may increase by 50% (Searchinger et al., 2018).

The positive effect of international development projects on global rates of hunger may recently have been overtaken by the negative effect of AGW. In 2015, the proportion of undernourished people on each continent varied between 7 and 19%; the world average was 11% in 2016 (Our World in Data, n.d.). This proportion decreased steadily in recent decades on all continents. But in low-income countries, the proportion of undernourished people was 27.2% in 2015, 28.2% in 2016, and 28.3% in 2017. Roser and Ritchie (2018) explained: