Why carbon footprinting (and carbon labelling)
only tells half the story
Rob Lillywhite & Rosemary Collier, University of Warwick, Wellesbourne, Warwick
Background
Carbon footprint of potato
•
A ‘carbon footprint’ is an estimate of all the greenhouse
gases (GHGs) associated with a process or product
•
It converts emissions of GHGs into a single carbon dioxide
equivalent (CO2e) value
•
In a farming and food context, the footprint represents
the total emissions of carbon dioxide (CO2), methane (CH4)
and nitrous oxide (N2O)
•
Auditing GHGs within an agricultural setting is not a
precise process, variation can be considerable, but there is
a tendency for the results to be presented with the same
confidence as in an industrial setting
Methodology and Approach
•
Overall, the average footprint was 126 g CO2e kg-1
•
Fertilizer and storage had the greatest influence overall,
whilst the manufacture of pesticides contributed little
•
Variation was considerable, which is not unexpected, since
inputs will vary as a result of biological, geological and
climatic differences between the places where crops are
grown
Carbon labelling of potato
•
Carbon labels are used to ‘inform’ consumers about the
carbon footprint of individual products but they aggregate
data and may actually provide little information of value
•
The approach followed the specifications laid out by
British Standards in PAS2050 ‘Specification for the
assessment of life cycle greenhouse gas emissions of
goods and services’
For example, Tesco King Edward potatoes have a carbon
footprint of 160 g CO2e per 250 g serving (640 g CO2e kg-1)
which incorporates five life cycle stages (production,
distribution, store, use, waste) (Tesco)
•
•
Carbon footprints were prepared for eight potato crops
from two different regions (Sussex and Lincolnshire) in the
UK (Defra, 2009)
The production stage contributes 211 g CO2e kg-1 (which
appears high in comparison to other studies) but it is the
‘use’ stage that has the greatest influence
•
•
The footprint was sub-divided into five categories (see
results section for categories)
The carbon footprint of cooking varies from 240 (boiling)
to 1025 (baking) g CO2e kg-1 which introduces enormous
variation into the footprint (a weighted average is used on
the label)
•
By incorporating the ‘use’ stage in its carbon label, Tesco
effectively hides information about the other four stages
since baking doubles the carbon footprint compared to
boiling
•
This approach may not be helpful to consumers trying to
understand the carbon burden of agricultural products, or
indeed different types of cooking.
•
Walker’s crisps
2008
2009
2011
Conclusions
Results
Category
Mean
Range
•
The values provided by carbon footprints and labels are
only estimates as high levels of variation are involved in
their calculation
g CO2e kg-1
Seed
Field operations
Fertilizer
Pesticides
Storage
10
28
50
5
33
7 – 15
19 – 46
33 – 67
2–9
3 – 81
•
However, carbon footprinting is a useful scientific tool for
assessing the carbon burden of production
•
Carbon labelling is currently not helpful to consumers
trying to understand the carbon burden of production
since values are variable and have little or no context
Total
126
64 - 218
•
Other environmental impacts, which some consumers
consider of greater importance, for example, pesticides
and water, are not addressed by current labels
Warwick Crop Centre
Rob Lillywhite
Rosemary Collier
www.warwick.ac.uk/go/wcc