How does your dinner affect the risk of 30,875 species of land-dwelling animal going extinct?

Dr Thomas Ball can tell you. Depending on what you’re eating he can calculate the likelihood of the global demise of every mammal, bird, amphibian and reptile over the next 100 years. He’ll tell you that not all dinners are equal.

“Every time anyone eats anything, it has an impact on the other species we share the planet with,” says Ball, a postdoctoral researcher in the Conservation Science Group in the University of Cambridge’s Department of Zoology.

“Rearing the cattle for one kilo of beef needs a huge amount of land, which displaces a lot of natural habitat. On average, that has a much bigger impact on species’ survival than growing one kilo of vegetable protein like beans or lentils.”

Ball isn’t just concerned with what we eat, but where it comes from. Beef imported to the UK from Australia and New Zealand - more common since Brexit - can drive up the environmental impact of our meat-eating because those countries are home to a much greater variety of species than the UK.

And while we can choose to buy locally reared beef, many of our everyday favourites like coffee, chocolate, and bananas can’t be grown in Britain at all. They’re produced in tropical regions, which are far richer in biodiversity than Britain, where converting tropical natural habitat to agricultural land impacts many more species.  

To add even more complexity, the same food crop grown in different locations can affect species extinction risk differently. Choose coffee grown in Costa Rica, for example, and your caffeine boost might be ten times worse for biodiversity than if you’d chosen coffee grown in Brazil.

“The coffee you choose to buy can really impact the likelihood of species going extinct," says Ball.

"This is not only because of the species being displaced to produce it, but also because farmers get very different yields from different coffee bean varieties for the same area of land,” he adds.

Ball is part of a Cambridge-led team putting real numbers on the biodiversity impacts of the food system. He’s using the ‘LIFE’ (‘Land-cover change Impacts on Future Extinctions’) metric, developed by the team to calculate how changes in land use, such as deforestation or habitat restoration, are likely to affect the extinction risk of 30,875 terrestrial vertebrate species worldwide.

Dr Alison Eyres, a postdoctoral researcher in the Conservation Science Group in the University of Cambridge’s Department of Zoology, used the metric to generate two maps showing the changes in the probability of terrestrial species extinction across the world in two scenarios. In the first, all remaining natural habitat is converted to farmland, and in the second all existing farmland is restored to its natural state.

While neither scenario is likely, at least in the short-term, the maps highlight the places in the world where mammals, birds, amphibians and reptiles would suffer or benefit the most from these land-use changes - and it’s not evenly spread.

The novelty of the LIFE approach is that it measures extinction risk for all species.

Though species already heavily impacted by habitat loss are more vulnerable to further declines, unlike other approaches LIFE also considers species currently thought to be doing well.

The high resolution and scalability allow users to calculate the impacts of land-use change across areas from 0.5 to over 1,000 square kilometres.

LIFE also takes a long-term perspective - forecasting impacts over a 100-year timeframe to account for the way species populations slowly die out, or rebound, following human-driven changes to the way land is used.

While we may have a degree of choice over what we eat as individuals, the UK government is making big decisions about where to source the foods that appear in our shops.

Ball’s work with Dr Jonathan Green at the Stockholm Environment Institute and the Joint Nature Conservation Committee (JNCC) has resulted in the LIFE metric becoming part of the UK Government’s toolkit for measuring the global environmental impacts of the UK’s consumption of agricultural commodities.

They’ve pulled together national data on the consumption and provenance of 140 food types, and integrated this with the LIFE metric to quantify the impact that different trade and agricultural policies might have on global species extinction risk – the first time this has ever been done.

"When it comes to decisions about producing food it’s not enough to focus on one country in isolation," says Ball.

"We have a UK agricultural policy that incentivises farmers to set aside more land for nature, and reduce food production. But if that means we’re making up the shortfall by relying on imports from more biodiverse places, it could cause far more damage to the species on our planet in the long run."

In the UK our food ‘extinction footprint’ is almost entirely due to imports.

For example, beef produced in Australia and New Zealand, which is now being imported to Britain in much bigger quantities since Brexit, is thirty to forty times more likely to lead to species extinctions than beef produced in the UK and Ireland.

By considering the productivity of any piece of land, Ball can figure out the ‘per kilogramme impact’ of each commodity per year. He says that eating more vegetables and less meat, and cutting down on ‘luxury’ crops like chocolate and coffee, could free up significant areas of land for restoration and save hundreds of the world’s species from extinction.