Are lower carbon diets healthier? Adam Briggs of the University of Oxford explains new research to model the effects of taxing GHG intensive foods.
With colleagues from the British Health Foundation Health Promotion Research Group, University of Oxford, and the School of Agriculture, Policy and Development, University of Reading, we estimated what a tax on foods, based on their greenhouse gas emissions, could do for UK population health.
Climate change has been described as ‘the biggest threat to global health of the 21st century’ with implications for altered disease patterns, increasing numbers of extreme climatic events, and food and water insecurity. Agriculture is thought to contribute around 10% of total greenhouse gas emissions and up to 30% if emissions from land-use change are included – such as those emissions resulting from deforestation. In the UK, the Climate Change Act commits the government to reduce emissions by 80% by 2050 from 1990 levels. However to do this within the agricultural sector will require more than just technological improvements; the population’s diet will need to change to become more sustainable. Researchers have previously investigated what a greenhouse gas friendly diet may look like but none have offered realistic ways of getting there. Furthermore, it is unclear whether those greenhouse gas friendly diets would truly be healthier.
Currently, the price of the food we eat does not reflect the wider harms to society of its greenhouse gas emissions. We modelled a tax that internalises those wider costs to society to estimate what may happen to the UK diet and the implications for health and greenhouse gas emissions.
We modelled two tax scenarios, one where only food groups with greenhouse gas emissions greater than average are taxed (all meats, fish, eggs, and coffee), and a second where in addition food groups with emissions lower than average are subsidised to create a tax-neutral scenario. We found that just taxing foods with high emissions had the potential to avert or delay 7,800 deaths per year in the UK from chronic diseases such as heart disease and cancer, as well as reduce UK greenhouse gas emissions from the agriculture sector by 18,600 kt/CO2 equivalents per year (about 7.5% of our estimate for total UK agricultural emissions). However, when we also subsidised food groups with lower than average emissions to create a tax neutral scenario, rather than a reduction we identified the possibility of an increased 1,900 extra deaths alongside an associated reduction in emissions of 15,200 kt/CO2 equivalents per year.
The tax modelled would put £1.76 on a kg of beef (the most taxed product), compared to 4p on a kg of poultry. The most heavily subsidised products included sugar and sweets (a reduction in price of 11p per kg). We used UK national survey data on shopping preferences to estimate how purchases of different food and drink products would change with a change in price. We also estimated what would happen to purchases of other food and drink groups as a result of increasing the price of beef, for example, and used the results to estimate the resulting average UK diet. We then used the number of calories in the resulting diet, as well as the amount of fats, fibre, salt, and fruit and vegetables, to predict the impact on deaths from chronic disease.
The results of this work predict important effects on both UK health and greenhouse gas emissions and highlight that although synergies between the two exist (from just taxing foods with high emissions), conflicts also may occur if subsidising foods with low emissions. In both scenarios, the major drivers for the changes in the number of UK deaths are change in calories. When taxing foods with high emissions, we estimate that the average daily calorie consumption would reduce by 28 kcals with large reductions in red meat consumption (of around 14%) compensated only partially by increases in fruit and vegetable fat consumption. When subsidising foods with low greenhouse gas emissions, similar reductions were found for red meat however significant increases in consumption were predicted for milk (6%), sugar (5%), fruit (3%), bread (2%) and vegetables (2%). This resulted in an increase in daily calorie consumption of 21 kcal/day. In both these tax scenarios, if calorie consumption were to stay the same as before the tax, UK deaths would be delayed or averted indicating that in both circumstances the overall composition of the diets is healthier.
It is important to note that our work does make some assumptions: the data on the greenhouse gas emissions from different foods is not perfect, we are unable to estimate how different subgroups of society may react to the tax, and we make no allowance for food wastage. However, we do demonstrate that realistic diets which would result in significant reductions in greenhouse gas emissions can also be good for population health, although it is important to note that conflicts may exist. And did I mention the estimated £2 billion/year revenue?
Dr Adam Briggs is an Academic Clinical Fellow in Public Health at the University of Oxford
The full paper: Adam D M Briggs, Ariane Kehlbacher, Richard Tiffin, Tara Garnett, Mike Rayner, Peter Scarborough. Assessing the impact on chronic disease of incorporating the societal cost of greenhouse gases into the price of food: an econometric and comparative risk assessment modelling study. BMJ Open 2013;3:e003543 can be accessed here.