4.1. Causation and attribution
Why is coal still burned in the U.S. although 52,000 Americans die from coal-related air pollution (excluding carbon) each year? A possible answer involves attribution. It is challenging to establish a causal connection between a given coal plant and the death of a specific future person. To overcome this challenge, instead, the 1000-ton rule assigns responsibility in proportion to the amount of carbon burned. If a company burns twice as much carbon as another, it kills twice as many future people. That is, the marginal death rate from future effects of global warming that are attributable to burning that coal is twice as high. The 1000-ton rule makes that proportionality specific. If the total number of deaths from climate change is known and the carbon emissions is known, the attribution is pro-rated in the same way as climate liability [
101].
Clearly, if a billion people are going to die prematurely due to AGW, those deaths should be prevented. If that question were asked to people from all walks of life and to leaders of diverse countries, the answer would surely always be the same. There is also universal agreement that preventing deaths is better than regretting them afterwards. Consequently, there should be universal agreement that humanity must immediately stop the killing of every individual future person, by immediately stopping the burning of every individual kiloton of carbon.
Those still profiting from emitting carbon might reasonably object that the chain of cause and effect between a carbon polluter’s action and a future resultant death is complex. How can polluters be sure that they are the cause of a given future death? A similar legal question might be asked of a gunman who points a gun at a victim and pulls the trigger with the intention of killing the victim. The attempt may fail for a range of reasons, some of which are beyond the gunman’s control: the gun might be faulty or not loaded, the gunman might miss the target, the target might suddenly move, the target might be injured but not killed, or the police may suddenly arrive, causing the gunman to flee. The gunman is nevertheless guilty of murder or manslaughter if two conditions are satisfied: the intent to kill can be demonstrated, and the victim dies as a result of the murder attempt. Similarly, fossil fuel industry leaders know in advance from media reports (even without reading this article, or other relevant academic literature) that their emissions will probably kill future people. That is true even if they do not intend to kill those people, but are merely being negligent while maximizing their profits while providing a public service in the energy marketplace. Again in that case, the chain of cause and effect is complex and can be interrupted in ways that are beyond the control of the industry. The industry’s leadership is nevertheless guilty if it can be demonstrated that they were informed in advance about the the deadly consequences of their actions or might reasonably have deduced those consequences themselves on the basis of publicly available information.
4.2. Energy Policy Implications
Several energy policy implications immediately fall from adopting a 1000-ton rule of analysis. The primary goal should be to decrease carbon emissions to zero. Anything that causes emissions should be eliminated. A first baby step toward that goal might be to ban advertising for fossil fuels, just as advertisements for tobacco and cigarettes are banned [
102]. In general, advertising should be banned if it encourages deadly habits (such as flying) and addictions (given the similarities between fossil-fuel use and addiction), in particular when the advertising is deliberately misleading (such as greenwashing). Likewise, consumers should be warned about the consequences of excessive or preventable fossil fuel use. For example, airline flight tickets could have a warning label: “Whereas smoking a cigarette takes 10 minutes off your life, an intercontinental return flight takes 13 days off the life of a future person.” Better still, the number of lost days for the specific flight in question could be calculated.
That raises another interesting issue. Whoever willfully causes 1000 tons of carbon to be burned, knowing the consequences in advance but doing it all the same, is guilty of killing a future person. Since it can be presumed there is no motive or intent to kill, this is not murder in a legal sense. If the polluter causes future deaths, they are guilty of manslaughter. Thus, measuring carbon emissions in human lives not only makes the numbers easier to understand – it also clarifies what the priorities should be on the policy front, as allowing policy to cause manslaughter is intuitively unacceptable. One approach to rectifying this problem involves carbon emission liability [
101,
103,
104,
105,
106]. Emissions bottlenecks have been recommended as liability targets to strategically reduce the greatest amounts of carbon emissions [
107].
Another interesting approach could be applying asset forfeiture laws [
108] (also referred to as asset seizure) to manslaughter caused by AGW. These laws enable confiscation of assets by the U.S. government as a type of criminal-justice financial obligation that applies to the proceeds of crime. Essentially, if criminals profit from the results of unlawful activity, the profits (assets) are confiscated by the authorities. This is not only law in the U.S. but is in place throughout the world. For example, in Canada, Part XII.2 of the Criminal Code, provides a national forfeiture régime for property arising from the commission of indictable offences [
109]. Similarly, ‘Son of Sam laws’ could also apply to carbon emissions. In the U.S., Son of Sam laws refers to laws designed to keep criminals from profiting from the notoriety of their crimes and often authorize the state to seize funds earned by the criminals to be used to compensate the criminal's victims [
110]. If that logic of asset forfeiture is applied to fossil fuel company investors who profit from carbon-emission related manslaughter, taxes could be set on fossil fuel profits, dividends, and capital gains at 100% and the resultant tax revenue could be used for energy efficiency and renewable energy projects or to help shield the poor from the most severe impacts of AGW. Future work is needed to determine over what time period should such laws be in force (e.g., seizure of past profits) and if additional penalties are necessary if companies purposefully misled the public to continue to profit from manslaughter (e.g., Exxon-Mobil’s climate communication [
111]). These laws would also apply to equipment manufacturers that enable fossil fuel extraction (e.g., pipeline equipment manufacturers). Such AGW-focused asset forfeiture laws would also apply to fossil fuel company executive compensation packages. Energy policy research has shown that it is possible to align energy executive compensation with careful calibration of incentive equations such that the harmful effects of emissions can be prevented through incentive pay [
112]. Executives that were compensated without these safeguards in place would have their incomes seized the same as other criminals benefiting materially from manslaughter.
Energy policy designed specifically to mitigate climate change should be prioritized in the following three main areas [
113]. In each area, the overriding need to save human lives justifies reduction in fossil fuel burning that is both large and fast:
Energy conservation: Improved energy efficiency and the rational use of energy should be supported by government programs. This can include industrial [
114], agricultural [
115], transportation [
116,
117], sustainable cities [
118], residential [
119] and at the household level [
120] energy efficiency in the developed world as well as the developing world [
121]. Energy efficiency, however, is not enough to bring emissions to acceptable levels [
122].
Evolution of the energy mix: Complete replacement of high carbon fuels (coal, oil and natural gas) by zero carbon content fuels (i.e., hydrogen, electricity, etc.) from renewable energy sources [
123,
124,
125] like: hydropower, wind, geothermal [
126], biomass and most importantly solar, which can be scaled to provide a sustainable society [
127]. Distributed generation (DG) with renewable energy should be encouraged as much as possible because many studies have shown DG customers provide a net benefit not only to non-DG customers, but also to the overall electrical grid [
128,
129]. Value of solar studies [
130] have confirmed the economic benefits surpass net metering rates and increasing the compensation for individuals investing in a renewable energy transition can be increased to at least meet this value. A broad range of policy tools have been introduced in countries and jurisdictions throughout the world that include [
131]: tradable emission rights, tax credits, and subsidies, as well as regulation such as feed-in-tariffs for renewable energy production.
Carbon waste management: Development of techniques to devalue carbon-intensive fuel such as carbon taxes [
132,
133,
134], and technical means for the capture and storage of CO
2 such as soil carbon sequestration [
135].
The results of this study indicate more aggressive policies may be needed than the gradual decarbonization of the past: i) instead of gradually increasing carbon taxes, ban the extraction of all fossil fuels [
136], ii) revoke the charters of fossil fuel companies and disperse their assets [
83], iii) retrain fossil-fuel workers en masse for renewable energy jobs [
137], iv) undercut fossil fuel regimes by giving renewable energy technologies to their citizens [
138], v) promote open-source technologies to erode the economies of fossil-fuel regimes [
139], vi) instead of complicated and time consuming rebates for energy conservation [
140], make mass purchases of energy conservation or renewable energy technologies, and make them freely available to all citizens (e.g., nationalizing/buying/constructing/subsidizing insulation plants or provide free insulation to everyone that will take it), vii) ban the sale of fossil fuel vehicles [
141] or even ban all cars [
142], viii) instead of incentivizing heat pumps [
143], ban natural gas stoves [
144] or even boilers [
145], ix) only allow development of net zero buildings (or better yet - positive energy buildings [
146]), x) as profiting from manslaughter is illegal, tax all fossil fuel-related investments at 100%, or xi) hold climate emitters as well as investors economically liable for harm caused by carbon emissions in the future [
101].
Some of these energy policies may appear extreme in historical context. Expressing carbon emissions in human lives clarifies the argument. For example, an outright ban on mining coal would negatively impact coal workers as they would lose their jobs and coal investors as they would lose their money. As there are both alternative sources of energy and alternative jobs, the cost and inconvenience of retraining coal workers for other types of employment and cutting unearned income for coal investors that have ignored decades of scientific warnings pales in comparison to the need to protect millions of human lives.
4.3. Limitations
Valerie Masson-Delmotte and colleagues warned humanity about the difference between 1.5°C and 2°C of warming [
147]. On that basis, AGW of 2°C was predicted to cause a billion premature deaths, spread across the next century or so. That raises the question of whether the number “one billion” is a reasonable estimate, or is it too high or too low? From a mathematical perspective, the number “one billion” is the peak of a rather broad probability distribution, within which the true value will fall – the number of people who actually die prematurely due to 2°C of AGW. The distribution is assumed to be log-normal: normal (bell-shaped) and symmetrical relative to logarithmic horizontal axis. The predicted number of deaths from 2°C of warming can be broken down in various ways:
Year: At present, the yearly death rate due to AGW is probably roughly one million. This figure is hard to estimate because AGW kills indirectly in diverse ways. The death rate was probably 300,000 per year in 2009 [
148], and has been increasing steadily since then. In 2010, the Madrid thinktank DARA estimated that AGW would cause one million human deaths per year by 2030 [
149]. At some point in the future, the death rate from various effects of AGW will overtake the number dying from air pollution – an independent negative effect of burning fossil fuels. Currently, some 7 million people are dying yearly from air pollution (either indoor or outdoor) [
150]. Altogether, hundreds of millions will die in coming decades as a result of fossil fuel burning, many of whom are already alive now. Further hundreds of millions of future AGW victims are not yet born.
Age: Victims will die at any age, but they will be predominately (very) young or (very) old at the time of death, those two groups being more vulnerable [
151,
152].
Location: UNICEF recently introduced the Children’s Climate Risk Index as shown in
Figure 1 [
145,
148]. The death rate relative to the population will be higher in climate-vulnerable countries such as Afghanistan, Bangladesh, Barbados, Bhutan, Costa Rica, Ethiopia, Ghana, Kenya, Kiribati, Madagascar, Maldives, Nepal, Philippines, Rwanda, Saint Lucia, Tanzania, Timor-Leste, Tuvalu, Vanuatu, and Vietnam.
Proximal cause: The deaths will be caused only indirectly by AGW. More direct causes of death will include heat and humidity, rising sea levels, freak storms, changing precipitation patterns, disappearing glaciers affecting water supplies, ocean acidification, more frequent bushfires, loss of biodiversity, and so on. Many of these side-effects of AGW will reduce food supplies, causing famines.
In August 2021, UNICEF warned that over one billion children are at extreme risk of the impacts of AGW [
153]. According to the Children’s Climate Risk Index (CCRI) [
153],
240 million children are exposed to coastal flooding;
330 million to riverine flooding;
400 million to cyclones;
600 million to vector borne diseases;
815 million to lead pollution;
820 million to heatwaves;
920 million to water scarcity; and
one billion children to dangerously high levels of air pollution.
Looking at the problem from different perspectives provides convergent evidence for an estimate of 1 billion deaths at 2°C of warming:
The estimate corresponds to 10% of projected future world population. All 10 billion humans will need food and fresh water to survive, and AGW will seriously affect both.
Since CO2 stays in the atmosphere for about a century, the prediction implies that, on average, 10 million additional deaths per year will be due to AGW.
If wet-bulb temperature exceeds skin temperature, perspiration can no longer cool the body. Already in 2022, this effect was life-threatening for a billion people in India and Pakistan [
154]. In the same countries in 2023, maximum temperatures were consistently above 40°C for over a two weeks [
161].
Future death rates are hard to predict because nothing of the kind has occurred in human history and the negative consequences of AGW as listed by the IPCC are diverse. They include: hunger, disease, direct heat, extreme weather events (which kill not only directly but also because they cause long-term health problems), violence (e.g., wars over diminishing resources such as water), and immigration. In a first approximation, the various AGW-related causes of death will add. It should be pointed out, there will also be interactions, so the whole will be greater than the sum of the parts [
155]. For example, people are more likely to die during an extreme storm if they are already weak from years of famine.
As global temperatures increase, uninhabitable areas will grow (e.g., in the Middle East). People in those areas who cannot rely on air conditioning or some other cooling strategy (e.g., cool swimming holes) during heat waves, or cannot afford to buy food and water or protect themselves in times of conflict, will be forced to migrate. They will join the swelling tide of climate refugees [
44], risking their lives to find a new place to live.
It has been estimated that there will be roughly one billion additional deaths for each degree of warming [
51], meaning that 3°C of warming would kill 2 billion people. That estimate is probably conservative if one considers the geographical areas that today occasionally suffer from deadly humid heat (with wet-bulb temperature exceeding skin temperature). Predicting the locations of such areas at different levels of warming using climate models, one might predict 3 billion deaths from direct heat alone at 3°C of warming [
156].
During the 21
st century, the population of Africa may rise by a factor of three, from 1.3 billion to roughly 4.2 billion [
157]. Those people will only survive if there is enough food. Along with other problems such as biodiversity loss and soil degradation, AGW will seriously affect food productivity. In the long term, it is challenging for Africa’s food production to be sustainably increased to feed its growing population. In addition, food distribution will be affected by conflict (the 2022 invasion of the Ukraine being an example). From what is known today about AGW, a massive, unprecedented, and seemingly never-ending catastrophe appears to be inevitable.
The calculations presented are conservative relative to some other published estimates of relevant death tolls. For example, Ziegler estimated that 35 million people die each year in connection with hunger [
158] – much more than the estimate of 10 million deaths per year in connection with poverty that is used here. Ziegler’s estimate is relevant because many of the people who will die prematurely in the future as an indirect consequence of AGW will die of hunger, and the estimate “one billion” can be made on the basis of expected increases in existing death rates from hunger. Today around 9 million people die every year from hunger and hunger-related diseases [
159]. This ethical challenge continues despite the global availability of more than enough human edible calories [
160], but several studies have indicated that the entire human population could be maintained even with a loss of all conventional agriculture during a global catastrophe [
161,
162].
4.4. Causes of death and future work
Causes of death often overlap. Intertwined effects include for example the effect of maternal mortality on neonatal survival rates [
163]. Whether poverty is the cause of death in a specific instance is difficult to operationalize. If a life could be saved by spending a reasonable amount of money, and that money was not spent, and the person died as a result, one can argue that poverty was the cause of death. Based on World Health Organization data Pogge [
164,
165] estimated that:
Some eighteen million human beings die prematurely each year from medical conditions we can cure – this is equivalent to fifty thousand avoidable deaths per day.
Moreover,
One-third of all human lives end in early death from poverty-related causes. Most of these premature deaths are avoidable through global institutional reforms that would eradicate extreme poverty. Many are also avoidable through global health-system reform that would make medical knowledge freely available as a global public good.
UNICEF has estimated that as many as 22,000 children are dying daily due to poverty, or 8 million per year [
159]. Another source claims that 35 million people are currently likely to die from hunger, presumably in the next few years [
166]. In addition to poverty, AGW will kill humans in multiple ways. By about 2070, up to 3 billion people will live in places that from today’s perspective will be too hot to survive in [
167]. Storms and floods kill directly, but also indirectly, by causing epidemics. Droughts kill when drinking water or food runs out. Rising seas kill when people are forced to leave their land and become migrants. In all these cases, poverty and AGW combine to cause human deaths.
Mortality from direct heat will depend on wealth or poverty as much as it depends on temperature. People with money own air conditioners that work when they need them, or have access to a cool refuge in thermal emergencies. If current trends continue, the most common cause of premature death in coming decades and centuries will be a combination of two broad factors: AGW and poverty. People with money will mostly be able to adapt. Others will not, with fatal consequences.
In the academic literature, death from direct heat is normally (and somewhat misleadingly) called “temperature-related mortality”. In fact, all causes of death in connection with AGW are “temperature-related”, some being more directly or immediately related to temperature than others. Famines, floods, and fires are less directly temperature-related: AGW changes rainfall, wind, and temperature patterns, which in turn cause famines, floods, and fires. To be clear, it may help to regard deaths from such events as “second-order” or “indirect” temperature-related mortality.
The number of deaths from direct heat may increase non-linearly (although not necessarily exponentially) as the temperature rises. In that way, the increase in mortality will not be the same for each fraction of a degree of AGW. For example, the increase in mortality caused by a global mean temperature increases from 1.5° to 1.6°C relative to pre-industrial temperatures will probably be less than the increase in mortality caused by raising global temperature from 2.5° to 2.6°C. The 1000-tonne rule applies to global warming of less than 2°C, and more work is needed to model possible non-linearities at higher temperatures.
Future work is needed to better attribute current death rates to AGW. The World Health Organization has estimated that between 2030 and 2050 climate change will cause 250,000 additional deaths per year due to malnutrition, malaria, diarrhea and heat stress [
59]. The WHO used a bottom-up estimate, extrapolating from existing death tolls without considering unexpected or non-linear effects in the future. These, of course, are hard to predict. They include war (e.g., conflicts over limited resources like water), migration (due to rising sea levels and other catastrophic effects of AGW), and effects of unprecedented floods, water shortages, and storms).
For the past few decades, the global death rate in connection with poverty has steadily declined in response to international development aid and economic growth in the Global South. Unfortunately, the global number of deaths from hunger (starvation) is now increasing again [
168]. The positive effect of economic growth in developing countries and international aid, which together previously caused mortality to decrease, is gradually being overwhelmed, not only by various negative effects of AGW (drought, flooding, fires, storms, disease spread, migration, conflict) but also by rising food prices linked to the emergence of global food monopolies; up to 90% of global trade in grain is controlled by just four corporations [
169]. In addition, in 2020 and 2021, the COVID-19 pandemic caused an additional increase in death rates in connection with poverty [
170]. Meanwhile, although the global death rate from malaria fell from 2010 to 2014, it increased again from 2015 to 2020, but the increase was partly due to changes in methodology for attributing cause of death [
171]. Future work is needed to disaggregate different causes of death attributed to AGW.
Given the many negative consequences of AGW, combined with biodiversity loss and population growth, our grandchildren will not be surprised when in the year 2100 the death rate in connection with poverty has doubled relative to 2000, from roughly 10 million to roughly 20 million per year. From the vantage point of the year 2023, doubling seems conservative, given the number and diversity of disastrous climate events in the news and corresponding predictions in mainstream peer-reviewed scientific journals.
Future AGW death rates will depend on other population trends. In many developed nations the birth rate has dropped far below the replacement rate already today. For example, South Korea only has 0.8 children per couple [
172] and even the U.S. is at 1.78, which is below the replacement rate [
173]. If these trends continue to spread into other nations, there may be fewer deaths caused by AGW simply because there will be fewer people. These trends, however, may be interdependent: some couples are avoiding children because of climate concerns (1 in 4 childless adults in the U.S.) [
174]. Overall, this review has made it clear there is far more work needed in this area to help guide appropriate energy policies.