The human cost of climate change: Estimating long-term mortality

A low-carbon lecture tour of Australia, July-August 2019

Richard Parncutt
  -- Watch the video here -- Read the paper here


Climate change is primarily a human rights issue. It will be a matter of life and death for enormous numbers of people — especially in developing countries. 
That is surely the main point, but almost no-one is talking about it. We are witnessing an eerie silence in both public media and academic publications. 

I addressed this issue in different Australian cities in July and August 2019, travelling only by train and bus (staying grounded; my return flight to Europe was presumably my last ever). My presentation was based on a manuscript that has since been published by Frontiers in Psychology.

All talks were open to the public and
lasted for about 45 minutes followed by questions. I thank the organisers at each location for their trust and support.

Time: Monday 15 July, 1 pm
Place: Monash University (
Clayton)9 Rainforest Walk, room 107
Organisers: School of Earth, Atmosphere and Environment; Sustainable Development Institute

Time: Thursday 25 July, 2 pm
Place: University of New South Wales (Kensington), Mathews Building, 4th floor, 
Seminar Room
Organisers: Climate Change Research Centre

Time: Mon 29 July, 12 noon
Place: University of New England,
Psychology Lecture Theatre
Organisers: Department of Psychology

Time: Thu 1 August, 10 am
Place: Queensland University of Technology (
Kelvin Grove), room OA-103 (O Block, A wing, ground floor)
Organisers: Public Health and Social Work, QUT

Time: Wed 7 August, 4 pm
James Cook University (Smithfield), Cairns Institute, room D3.054
(video-linked to ATSIP 145-030 Townsville)
Organisers: Centre for Tropical Environmental and Sustainability Science
Info - Video

Time: Friday 9 August, 6:30 pm 
("green drinks")
Place: Fish Inn 
Organisers: North Queensland Conservation Council

Time: Fri 23 August, 3:30 pm
Charles Darwin University (Casuarina), Room Yellow 1.1.39 
Research Institute for the Environment and Livelihoods (RIEL)

Time: Friday 30 August, 1 pm
University of Adelaide (North Terrace), G10 Benham Lecture Theatre
Organisers: The Environment Institute
Info - Video


So far, global mean surface temperature has increased by about 1°C relative to the pre-industrial period due to human activity  mainly carbon emissions and deforestation. In 2018, the international community of climate scientists, represented by the Intergovernmental Panel on Climate Change (IPCC), explained that a further temperature rise of 1°C (making 2°C altogether) will have catastrophic global consequences. Many of these consequences can be avoided by limiting the increase to 1.5°C.

We can achieve the 
1.5°C goal by halving global emissions by 2030 and approaching net zero by 2050. Currently, no such international agreement exists. If the 2015 Paris participants do what they promised (and experience suggests otherwise), global mean surface temperature will rise well above +2°C. The damage will be existential and irreversible.

 2°C increase would cause a very large number of premature human deaths in many different ways. Among other things, it would exacerbate the existing death toll in connection with poverty: hunger, curable disease, preventable disease, violence. This rate, which is currently some 10 million per year, could double by 2100.

In a very rough first-order approximation, 
2°C will cause a billion premature deaths, spread out over one to two centuries. That's 10% of a future global population of 10 billion. I will present diverse arguments in support of this preliminary estimate, including various best- and worst-case estimates that take into account estimated probabilities of different possible catastrophic outcomes.

The 1000-tonne rule

To cause 2°C of warming, humanity will have burned approximately a trillion tonnes of carbon, creating about 3.7 trillion tonnes of CO2. If 2°C causes a billion premature deaths, a future person is dying prematurely every time we burn 1000 tonnes of carbon. The implications of this simple rule are staggering:
This may initially seem like an abstract calculation a game with numbers. But the people in these examples are real. Many of them are already alive now, as children. They could die anywhere in the world and they could die for many different reasons. If you are reading this text, you probably live in a rich country, so your childen and personal acquaintances will probably not be mortally affected. Most of the victims will die in poorer or tropical countries. The most common direct causes of death will be hunger, curable/preventable disease, violence, or direct heat. If humanity manages to get climate change under control, most of the deaths will happen during the coming two centuries.

In the many lively discussions following this talk in different Australian cities, no-one argued that my main quantitative estimates, based on IPCC reports,
might be too high or too low. Those estimates are:
Nor did anonymous expert reviewers question these estimates when I submitted them to a leading international peer-review journal. 

Just how bad is this?

Fossil fuels are not all bad. On the contrary: until now, burning carbon has had an enormous positive effect on human quality of life and longevity. Over the past couple of centuries, life expectancies have steadily increased in industrialized countries
largely due to the ready availability of energy for diverse purposes (transport, agriculture, heating, building). That is surely one of humanity's greatest achievements.

We should also remember that any major infrastructure project causes future premature deaths. Consider West Gate Bridge in Melbourne, part of which collapsed in 1970, killing 35 construction workers. It is impossible to completely eliminate the risk of bridge collapse. A typical large bridge will collapse sometime during its lifetime with a given probability. Let's assume the probability of collapse is 0.1% and the human cost is typically 100 lives. If that is true, constructing a typical bridge effectively kills 1/10 of a person. But that human cost is surely outweighed by the benefits of the bridge to millions of users.

Nuclear power plants are a contrasting example. The Chernobyl disaster in 1986 may have caused the premature deaths of as many as a million people
mainly because radiation increases the risk of cancer. If the probability of such a disaster in a typical nuclear reactor is 0.1%, each new reactor is effectively causing 1000 premature deaths. Most people would agree that a risk of that magnitude is too high by comparison to the benefit of the electricity generated by the plant, even without considering the waste problem.

But these "everyday" risks pale into insignificance by comparison to fossil fuels, which according to the 1000-tonne rule are currently killing about 10 million future people worldwide every year. Having appreciated the massive pros and cons of fossil fuels, the challenge now is to radically change how we generate and use energy. We need to maintain what we have achieved in terms of human quality of life and longevity for future generations.

The importance of honesty

The right to life of today's children and future generations is clearly more important than today's economic wellbeing. Agreement on this point is almost universal, given that hardly anyone would dare to publicly contradict it. If we are honest about that, big changes are urgently necessary.
We must also increase the global rate of photosynthesis by stopping deforestation and promoting reforestation (as well as implementing geoengineering solutions, provided the benefits are clearly greater than the dangers), and take appropriate measures to curb global population growth. But even if such projects are very successful, and regardless of what happens in the political/corporate domain, the average person will still have to drastically reduce personal emissions.

The macro and the micro levels are equally important. To have any hope of achieving the 1.5°C target, we must combine them. Each motivates the other.

To those who say we "cannot" change the system in this way or we "cannot" stop flying, driving, and eating meat, there is an easy answer: Tell the truth. We can do these things, and we know it. Humans can do many things. We can also kill millions of future people and risk the extermination of humanity, if we want. The question is, what do we want? 

The statements in italics are not necessarily political demands or value judgments. They can be regarded merely as logical conclusions that follow directly from widely accepted facts and values. In general, we are free to choose between honesty and denial (or between caring or not caring about children and future generations). If everyone agreed to be consistently honest (or to care), implementation of the statements in italics (or something similar) would be inevitable. Again, this is not necessary a political claim or value judgment, but merely a logical conclusion. Is dishonesty the only thing standing in our way?

Responding rationally and constructively

Many people feel overwhelmed by these ideas. The temptation to either panic or deny
is understandable. How can we break free from extreme reactions and develop a rational, constructive response? The talk will draw on diverse academic disciplines including physics, chemistry, biology, ethics (philosophy), psychology, sociology, medicine, economics, law, and political science. It will be accessible for experts in all disciplines and all concerned citizens, regardless of academic background.

Abstract. Greenhouse-gas emissions are indirectly causing future deaths by multiple mechanisms. For example, reduced food and water supplies will exacerbate hunger, disease, violence, and migration. How will anthropogenic global warming (AGW) affect global mortality due to poverty around and beyond 2100? Roughly how much burned fossil carbon corresponds to one future death? What are the ethical, legal, psychological, medical, political, economic implications? Predicted death tolls are crucial for policy formulation, but uncertainty increases with temporal distance from the present and estimates may be psychologically biased. Order-of-magnitude estimates can be made by comparing literature from diverse relevant disciplines. The carbon budget for 2°C AGW (roughly 1012 tonnes of carbon) will indirectly cause roughly 109 future premature deaths (10% of projected maximum global population), spread over one to two centuries. This zeroth-order prediction is relative and in addition to existing preventable death rates. It lies between likely best- and worst-case scenarios of 3 x 108 and 3 x 109, corresponding to plus/minus one standard deviation on a logarithmic scale in a Gaussian probability distribution. It implies that one future premature death is caused every time roughly 1000 (300 to 3000) tonnes of carbon are burned; therefore, any fossil-fuel project that burns millions of tons of carbon is probably indirectly killing thousands of future people. The prediction may be considered valid, accounting for multiple indirect links between AGW and death rates in a top-down approach, but unreliable due e.g. to the uncertainty of climate change feedback and interactions between physical, biological, social, and political climate impacts (e.g., ecological cascade effects, co-extinction). Given universal agreement about the value of human lives, a death toll of this unprecedented magnitude must be avoided at all costs. As a clear political message, the “1000-tonne rule” can be used to defend human rights, especially in developing countries, and to clarify that climate change is primarily a human rights issue.

Biography. Richard Parncutt studied at the University of Melbourne and
the University of New England (Armidale, NSW). He has a BSc with honours in physics and an interdisciplinary PhD in psychology, music and physics. His other research addresses the perception and cognition of musical structure, music performance, the origins of tonality and music, and musicological interdisciplinarity (more). He now lives in Graz, Austria (more). In 2018, he organized an innovative multi-location semi-virtual conference (more) to reduce academic carbon footprints (more).

Nolt, J. (2011). How harmful are the average American's greenhouse gas emissions? Ethics, Policy and Environment, 14(1), 3-10.

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