Climate change – key terms

This resource provides explanations of some of the key terms and concepts encountered when learning about climate change. It includes references to New Zealand’s greenhouse gas profile.

• Anomaly
• Anthropogenic global warming
• Carbon dioxide (CO₂)
• Carbon footprint
• Carbon neutral
• Carbon sink
• Emissions
• Extreme weather
• Fossil fuels
• Greenhouse gases
• Gross greenhouse gas emissions
• Methane (CH₄)
• Net greenhouse gas emissions
• Nitrous oxide (N₂O)
• Parts per million (ppm)

Anomaly

An anomaly is a variation from a baseline measurement. The World Meteorological Organization recommends the 30-year reference period from 1961–1990 as the baseline for calculating anomalies for long-term climate change assessments. It is used for reporting purposes to show climate change over time.

Anomalies can also be measured against the current climate normal, for example, 1991–2020. These anomalies are presented as ‘normal’ for a daily weather report.

Anthropogenic global warming

The rise in regional and global temperatures caused by human-produced greenhouse gas emissions, including burning of fossil fuels and intensive agriculture.

Carbon dioxide (CO₂)

A naturally occurring gas in the Earth’s atmosphere. It is the principal greenhouse gas produced by human activities. Humans added about 42 gigatonnes (Gt) of carbon dioxide to the atmosphere in 2018 – more than 190 times the weight of all the people in the world.

New Zealand’s gross CO₂ emissions in 2016 were about 35,000 kilotonnes.

Carbon footprint

A carbon footprint corresponds to the whole amount of greenhouse gases produced to (directly and indirectly) support a person’s lifestyle and activities. It can also refer to the amount of carbon emitted during an activity or the manufacturing of a product.

Carbon neutral

A process in which there is no net release of carbon dioxide. The amount of carbon taken out has to equal the amount of carbon released. An organisation can achieve carbon neutrality by offsetting – balancing emissions by funding an equivalent amount of carbon savings via tree planting and other projects.

Carbon sink

Anything that absorbs more carbon dioxide than it emits. Natural examples of carbon sinks are forests, soil and the oceans.

Emissions

The release of greenhouse gases from a human activity such as coal-burning power stations, car exhaust or methane from farm animals. Emissions can also come from natural sources such as volcanoes.

Different approaches for estimating our emissionse include:

• a production-based approach that counts any emissions produced within our borders
• a consumption-based approach that counts emissions within our borders released to produce goods and services used here and import emissions (emissions released overseas to produce the goods and services we use in New Zealand).

The Ministry for the Environment generates New Zealand’s Greenhouse Gas Inventory annually. It is the key source of evidence on the country’s greenhouse gas emission trends.

Extreme weather

Any type of severe or unseasonal weather such as heavy rainfall, droughts, extended heat waves or cold spells that is much higher or lower than what is expected. Extreme weather events are predicted to become more common due to extra energy entering the atmosphere.

Fossil fuels

Coal, oil and natural gas are examples of fossil fuels. They are called fossil fuels because they come from ancient carbon sources (plants and animals). When burned, fossil fuels release the carbon they once stored.

In New Zealand, road transport makes the largest contribution to our carbon dioxide emissions due to burning fossil fuels.

Greenhouse gases

Greenhouse gases are natural and human-produced gases that trap heat in the Earth’s atmosphere and warm the Earth’s surface. Water vapour is the most common greenhouse gas. Carbon dioxide, methane and nitrous oxide are the most common human-generated greenhouses gases.

New Zealand has an unusual greenhouse gas profile for a developed country. Almost half of our greenhouse gas emissions come from agriculture, and only a small proportion comes from electricity generation, which is the opposite to many other developed countries.

Gross greenhouse gas emissions

Gross greenhouse gas emissions are the total emissions from energy, industrial processes and product use, agriculture and waste. They do not include natural sources of emissions such as those from biological processes or volcanoes.

In New Zealand, gross greenhouse gas emissions were about 24% higher in 2018 than in 1990. From 2008–2018, emissions have changed little despite increases in gross domestic product (GDP) and population.

Methane (CH₄)

Methane is a gas that is naturally emitted from wetlands and wildfires. It is also associated with agriculture, landfills and coal mining. Methane warms the climate about 25 times more than an equivalent amount of carbon dioxide.

About 86% of New Zealand’s methane emissions come from ruminant livestock – sheep, cattle, goats and deer.

Net greenhouse gas emissions

Net greenhouse gas emissions include gross emissions combined with emissions and removals from land use, land-use change and forestry. Land-use change is the conversion of land from one purpose to another.

New Zealand’s net emissions have increased by 57% since 1990.

Nitrous oxide (N₂O)

Nitrous oxide is a gas that is a natural part of the nitrogen cycle. However, about 40% of total nitrous oxide emissions come from human activities. Nitrous oxide is emitted from agricultural soils (via animal urine patches), fossil fuels and industrial activities. Nitrous oxide warms the climate about 300 times more than an equivalent amount of carbon dioxide.

Most of New Zealand’s nitrous oxide emissions come from the soil – microbes convert nitrate in urine patches to nitrogen gases.

Parts per million (ppm)

A unit of measurement for the concentration of greenhouse gases in the atmosphere. Atmospheric carbon dioxide concentrations have been monitored continuously at Mauna Loa Observatory in Hawaii. In March 1958, the CO₂ concentration was 313 ppm by volume. In May 2020, the concentration reached a seasonal peak of 417 ppm by volume.

Baring Head, a monitoring station at the southern end of the North Island, has been recording atmospheric CO₂ concentrations since 1972 – the longest continuous record in the southern hemisphere. It has also documented the rise of CO₂ from around 320 ppm in 1972 to well over 409 ppm in September 2019.