Here is an important tool to help us understand the uneven distribution of GHG emissions by consumption category and country: The Carbon Footprint of Nations website from the Norwegian University of Science and Technology, based on a global trade-linked analysis using the input-output method.
Here is how global emissions break down by purpose:
- 72% of global emissions are related to household consumption
- 10% of emissions are from government consumption
- 18% of emissions are attributed to investments
And here is the break down by consumption category:
- Food accounts for 20% of GHG emissions
- Operation and maintenance of residences contribute 19%
- Transportation is 17%
The IPCC estimates that agriculture contributes 13.5% of global emissions, based on land area used for agriculture, numbers of livestock and other details (but not including land use change). The 20% share of food is based on an input-output analysis and presumably includes processing, packaging and other added value beyond agriculture -- a very useful estimate if accurate.