Knowing your emissions

Thought leadership by Farmlands' Head of Nutrition and Animal Health Dr Rob Derrick.

Global warming is arguably the largest single threat facing humankind. It’s not going away and with the Climate Change Commission’s draft emission target report being released in January 2021, the call has been put out to New Zealanders to create fewer emissions than we do now.

It is the Farmlands’ Growth and Innovation team’s responsibility to understand the challenges these targets will impose and what solutions are available to actively create positive outcomes for both producers and consumers. With greenhouse gases, methane and carbon being the number one topic across the boardroom and over the farm gate, it can be easy to feel overwhelmed with what it all means and what the difference is.

The basics

Greenhouse gases (GHG) warm the earth by absorbing energy and slowing the rate at which energy escapes to space. GHG differ in their ability to absorb energy and how long they stay in the atmosphere and are compared by Global Warming Potential (GWP)1 . 1 tonne of carbon dioxide has a GWP score of 1, methane is at 28-36 and nitrous oxide hits 265-298 times that of carbon dioxide within a 100-year timeframe. Methane is 75 times more potent than carbon dioxide, but typically lasts just 12 years in the atmosphere. Nitrous oxide emitted today remains in the atmosphere for more than 100 years on average so its potential to cause global warming is greater.

The future

New Zealand farmers do have the wherewithal to meet the food needs of a global population while also reducing net greenhouse gas emissions. With strong targets and solutions in place, such as building farm plans and managing land use, together we can all make a difference.

1) United States Environmental Protection Agency. (n.d.). Understanding Global Warming Potentials. https://www.epa.gov/ghgemissions/understanding-global-warming-potentials 2) Ministry for the Environment. (2018). New Zealand’s Greenhouse Gas Inventory. https://www.mfe.govt.nz// files/media/Climate%20Change/new-zealands-greenhouse-gas-inventory-1990-2018-vol-1.pdf

Gases that contribute to the greenhouse effect:

Carbon Dioxide (CO2 )

Carbon dioxide is the most important greenhouse gas — accounting for over 80 percent of all US greenhouse gas emissions from human activities, compared to 45 percent of NZ emissions in 20172. Carbon dioxide enters the atmosphere through burning fossil fuels, solid waste and trees and from some chemical reactions like making cement. Carbon dioxide is removed from the atmosphere — often referred to as sequestration — when it is absorbed by plants, soil and the ocean. Sequestration is one way of helping slow climate change.

Nitrous oxide (N2O)

Nitrous oxide (laughing gas) is emitted from soil when urine, faeces and fertilisers are broken down by microbes in the soil. This occurs more often when the soil is waterlogged. In 2017, nitrous oxide accounted for approximately 11 percent2 of New Zealand’s GHG emissions (in terms of tonnes of carbon dioxide equivalents). Of all the nitrous oxide emissions, over 94 percent2 came from agricultural soils, mainly due to urine and dung deposited by grazing animals. Although it does not contain carbon, nitrous oxide is considered within the carbon footprint of an operation.

Methane (CH4 )

Methane is a by-product of rumen fermentation and is classed as enteric (coming from the digestive tract) as opposed to the methane created in peat bogs. Methane was estimated to contribute 42 percent2 of New Zealand GHG emissions in 2017 (in terms of tonnes of carbon dioxide equivalents). In the rumen, methane plays an important role as a hydrogen sink — it helps to mop up harmful hydrogen which lowers rumen pH. A low rumen pH can cause rumen acidosis if unchecked.

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