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Pressures on our atmosphere and climate

The climate and weather we experience around New Zealand are influenced by a number of factors. These include our geography and position on the globe, the time of year, natural drivers of variability, and human activities.

New Zealand is a set of islands in a remote location in the mid-latitude westerlies of the South Pacific Ocean. Our two main islands stretch across a wide span of latitudes (34–47° south), with mountain ranges affecting the patterns of wind and rain. This varied geography contributes to marked variations in climate across the country, particularly between the east and west, and to extreme weather events, such as flooding and droughts.

Natural climate variability

Our climate varies naturally over timescales ranging from months to millennia. For example, 'wobbles' in Earth's orbit drive ice ages every 100,000 years or so, changes in solar irradiance (or sunspots) occur roughly every decade, large volcanic eruptions can cool the planet for 1–3 years, and then there are climate oscillations, which affect the climate from year to year.

Climate oscillations

A climate oscillation is a natural pattern of changes in air pressure, sea temperature, and wind direction that is consistent over a period of a few months to several decades. Three oscillations in particular influence New Zealand's weather and climate. These are El Niño Southern Oscillation (ENSO) (with three phases: neutral, El Niño, and La Niña), Interdecadal Pacific Oscillation (IPO), and Southern Annular Mode (SAM). The influence of these oscillations on our weather and climate (see box 2) is important for recreation and our agricultural and other industries, such as construction.

Box 2      Climate oscillations influencing New Zealand's weather and climate

El Niño Southern Oscillation

An El Niño phase during summer can lead to increased westerlies, with more rain in the west and drought in the east.See Environmental indicators Te taiao Aotearoa: El Niño Southern OscillationENSO is the cyclical change in the movement of wind and warm equatorial water across the Pacific Ocean. An El Niño or La Niña phase of ENSO occurs every two to seven years and lasts around a year (NIWA, nd-a). In New Zealand, the impacts vary between individual phases, but over summer, an El Niño tends to lead to increased westerly winds, with more rain in the west and drought in the east (Salinger & Mullan, 1999). By comparison, a La Niña may lead to fewer westerly winds and more north-easterly winds in New Zealand. This tends to cause warmer temperatures around the country and more rain in the northeast of the North Island and less in the south and southwest of the South Island.

 

Southern Annular Mode

 	SAM has generally been increasing (becoming more positive) since 1970.See Environmental indicators Te taiao Aotearoa: Southern Annular Mode SAM, also known as Antarctic Oscillation or the Southern Hemisphere Annular Mode, describes the north to south movement of westerly wind that circles the South Pole, dominating the middle to higher latitudes of the Southern Hemisphere. In New Zealand, a negative SAM phase is associated with more frequent westerly winds, unsettled weather, and storms over most of the country. The opposite applies in a positive SAM phase. New Zealand generally experiences relatively light winds and settled weather during a positive SAM phase (NIWA, 2007). One phase of SAM can last for several weeks, but phases change quickly and randomly.

SAM has generally been increasing (becoming more positive) since 1970 (Marshall, 2003). This increasing trend is largely associated with ozone depletion (NIWA, 2006).

 

Interdecadal Pacific Oscillation

 	A positive phase of IPO is linked to stronger west to southwest winds, more rain in the west, and drier conditions in the north and east.See Environmental indicators Te taiao Aotearoa: Interdecadal Pacific OscillationIPO is a pattern of sea-surface temperature and sea-level pressure changes over the Pacific basin that occur over 20- to 30-year timescales. It affects the strength and frequency of ENSO (Salinger et al, 2001). In New Zealand, a positive IPO phase is linked to stronger west to southwest winds, more rain in the west, and drier conditions in the north and east. The opposite occurs in a negative phase. IPO was in a negative phase from 1999 to 2013, then switched to a positive phase.

 

Greenhouse gas emissions from human activities

As well as natural variability, the global climate is changing as a result of increased greenhouse gases and aerosols in the atmosphere from human activities, mainly burning fossil fuels but also changing land use and emissions from other activities (including industry and agriculture). An example of land-use change is converting forested land (which stores large amounts of carbon until the trees are felled) for agriculture and urban developments.

Carbon dioxide, methane, nitrous oxide, and fluorinated gases (human-made gases found in products such as refrigerators, air-conditioners, foams, and aerosol cans) are the most important greenhouse gases emitted from human activity because they accumulate in the atmosphere and absorb additional energy, making Earth warmer than it would otherwise be.

Different greenhouse gases can have different effects on Earth’s warming, for example, through how long they stay in the atmosphere (their ‘lifetime’) and their ability to absorb energy or trap heat (their ‘radiative efficiency’). The global warming potential (GWP) index measures how much each gas contributes to global warming over a given time period compared with carbon dioxide, which has a GWP value of 1. GWP is usually measured over a time period of 100 years. For example, the 100-year GWP of methane describes the effect that emitting 1 kilogram of this gas will exert on atmospheric warming over 100 years relative to the effect of emitting 1 kilogram of carbon dioxide (United Nations Framework Convention on Climate Change (UNFCCC), 2006).

Researchers can use the GWP to add emissions estimates of different gases and compare the effects of reducing emissions from different human activities. Figure 3 shows the most important greenhouse gases emitted from human activity, some of the primary New Zealand sources of these gases, their lifetime in the atmosphere, and GWP.

Figure 3

Note: New Zealand uses the global warming potential (GWP) index in its reports to the United Nations Framework Convention on Climate Change. GWP values are updated from time to time as knowledge of the lifetime and radiative efficiency of gases is refined.

This figure shows important greenhouse gases in the atmosphere and their New Zealand emission sources.

Increasing global emissions

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Global gross greenhouse gas emissions increased 51 percent from 1990 to 2013.

See Environmental indicators Te taiao Aotearoa: Global greenhouse gas emissions

Greenhouse gas emissions enter the atmosphere and, given their long lifetimes, accumulate and spread around the globe. This means that despite New Zealand’s geographic remoteness, we cannot avoid the effects of increasing global emissions.

From 1990 to 2013, global gross greenhouse gas emissions from human activities increased 51 percent (see figure 4). The global emissions for 2013 comprised mostly carbon dioxide (76 percent), methane (16 percent), and nitrous oxide (6 percent).

Atmospheric carbon dioxide concentrations have risen steadily since the industrial revolution (around the mid-18th century) (IPCC, 2013). Records from Baring Head, Wellington show that carbon dioxide concentrations over New Zealand increased 23 percent from 1972 (when measurements first began) to 2016 (see box 3). This is consistent with global trends.

In 2016, global concentrations of atmospheric carbon dioxide passed the symbolic threshold of 400 parts per million (see box 3) (NASA, 2017b). This is the highest level of carbon dioxide in our atmosphere in at least the last 800,000 years (IPCC, 2013).

Figure 4

Note: Net emissions include emissions and removals as a result of land-use change and forestry (LUCF). GHG emissions are in metric tons of CO2 equivalent (MtCO2-e). The Kyoto Protocol set 1990 as the base year for signing parties’ national greenhouse gas inventories.

This graph shows gross and net global greenhouse gas emissions, 1990–2013. Visit the MfE data service for the full breakdown of the data.

Some countries are reducing their emissions. For example, from 1990 to 2013, the United Kingdom reduced its emissions of carbon-dioxide equivalents by 26 percent, Sweden by 25 percent, and France by 11 percent (CAIT, 2017). Any country’s ability to decrease their emissions depends on not only the steps they take to reduce emissions but also their circumstances, such as their economic dependence on greenhouse-gas-intensive industries, changing energy sources, accessibility and availability of emission-reducing technologies, and population changes.

New Zealand’s emissions

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New Zealand’s gross and net greenhouse gas emissions increased 24 and 64 percent respectively, from 1990 to 2015.

See Environmental indicators Te taiao Aotearoa: New Zealand’s greenhouse gas emissions

Over the period 1990 to 2015, New Zealand’s gross and net greenhouse gas emissions increased 24 and 64 percent respectively, although most of the increase in gross emissions occurred by 2005.

Net emissions take into account the carbon dioxide absorbed by forests and then released when the trees are felled. The large increase in net emissions is the result of increases in gross emissions combined with higher logging rates in production forests (Ministry for the Environment, 2017a).

Population growth and increased domestic production have driven the increase in gross emissions since 1990 (Ministry for the Environment, 2017a). Most of these increases came from agricultural production and road transport. Agricultural emissions from livestock digestion (mostly methane) rose 5 percent, while emissions from agricultural soils (mostly nitrous oxide from nitrogen fertiliser use and excrement from grazing livestock) rose 51 percent. Road transport emissions (mostly carbon dioxide) rose 78 percent (see table 1).

The increased agricultural emissions were mainly due to increased dairy production and were partly offset by a drop in emissions from sheep as a result of reduced sheep numbers. Increasing emissions from energy generation have been moderated by an increase in the share of energy from renewable sources (Ministry for the Environment, 2017a).

New Zealand’s Intended Nationally Determined Contribution under the 2015 Paris Agreement on Climate Change is a target to reduce our greenhouse gas emissions to 30 percent below 2005 levels by 2030.

High per capita emissions

8“…New Zealand currently has the fifth-highest level of emissions per person in the OECD.”OECD, 20177As expected from a country with a small population, New Zealand’s contribution to global gross greenhouse gas emissions is small (0.17 percent of global gross greenhouse gas emissions), but our per capita emissions are at the high end compared with most other developed nations, based on 2013 data (CAIT, 2017).

New Zealand has the second-highest level of emissions per gross domestic product unit of the 35 OECD countries and the fifth-highest emissions per capita (OECD, 2017).

New Zealand’s high per capita emissions are mainly due to our unusually large share of agricultural emissions and high per capita car ownership rate. New Zealand’s car ownership is the highest in the OECD (OECD, 2017). Our car fleet is also relatively old by OECD standards, resulting in high fuel consumption for each kilometre travelled.

Table 1    Main sources of New Zealand’s greenhouse gas emissions

EMISSIONS CATEGORY

MAIN GHG PRODUCED

TOTAL GHG EMISSIONS IN 2015 (KT CO2-e)

PERCENT OF GROSS NZ GHG EMISSIONS IN 2015

PERCENT CHANGE SINCE 1990

Digestion from livestock

Methane

28,091

35

+ 5

Road transportation

Carbon dioxide

13,282

17

+ 78

Agricultural soils (direct source, eg fertilisers, animal urine, and crop residues; indirect sources, eg atmospheric deposition and nitrate leaching)

Nitrous oxide

7,917

10

+ 51

Manufacturing industries and construction (iron and steel; non-ferrous metals; chemicals; pulp, paper, and print; food processing, beverage, and tobacco; non-metallic minerals; other)

Carbon dioxide

6,810

8

+ 43

Industrial processes and product use (minerals; chemicals; metals; non-energy products from fuels and solvent use; substitutes for ozone-depleting substances; other)

Carbon dioxide

5,280

7

+ 47

Grassland (conversion of land, primary forest, to grassland; existing grassland)(1) 

Carbon dioxide

4,652

Not applicable

+ 430

Public electricity and heat generation

Carbon dioxide

4,041

5

+ 16

Solid waste disposal

Methane

3,626

5

– 4

 

1.      Percent of gross New Zealand greenhouse gas (GHG) emissions cannot be calculated for grasslands because they are not included in gross emissions totals. Emissions in this category are largely from the loss of carbon associated with converting forest land to grassland.

Note: kt CO2-e – kilotonnes carbon dioxide equivalent. As the table only covers the main sources of New Zealand’s emissions, the percentages in column four will not add up to 100 percent.

Our emissions profile

Our agricultural emissions are large compared with other developed countries, but we have a smaller share of emissions from the energy and transport sectors (see figure 5). Unlike most countries where fossil fuel electricity generation is the primary source of carbon dioxide emissions, in New Zealand, we generate over 80 percent of our electricity from renewable resources (OECD, 2017).

Figure 6 shows the sources and relative contribution of greenhouse gas emissions in New Zealand’s emissions in 2015.

For more information on New Zealand’s greenhouse gas emissions, see New Zealand Greenhouse Gas Inventory and Interactive Emissions Tracker.

Figure 5

This figure compares the gross greenhouse gas emissions profiles of New Zealand and a typical developed country.

Figure 6

This figure shows New Zealand’s greenhouse gas emissions profile in 2015. Visit the MfE data service for the full breakdown of the data.

Box 3      Increasing greenhouse gas concentrations

 	Since 1972, atmospheric carbon dioxide concentrations measured at the Baring Head monitoring station have increased 23 percent.See Environmental indicators Te taiao Aotearoa: Greenhouse gas concentrationsGreenhouse gas concentrations have been measured at the Baring Head Clean Air Monitoring Station, overlooking the Cook Strait near Wellington, since 1972. Baring Head
lies in the perfect position to receive southerly air from areas with no local human activity and therefore represents background concentrations of greenhouse gases over the Southern Ocean.

The Baring Head monitoring station boasts the longest-running continuous record of atmospheric carbon dioxide in the Southern Hemisphere. Data from the internationally recognised site contribute to our global understanding of greenhouse gases and the effect of human activity on Earth's atmosphere. Carbon dioxide was the first gas to be measured at the site in 1972, followed by methane in 1989 and nitrous oxide in 1996. Isotopes (variants) of these gases have been measured nearby since 1954 and are used to understand sources that contribute to the build-up of these gases.

Since 1972, levels of atmospheric carbon dioxide have increased 23 percent, from 326 parts per million to 401 parts per million in December 2016, surpassing the symbolic threshold of 400 parts per million (see 400 parts per million below). Levels of atmospheric methane and nitrous oxide increased 9 percent from 1989 and 6 percent from 1996, respectively. The Baring Head record is consistent with global trends.

Baring Head measurement station near Wellington. (Photo: Dave Allen, NIWA)

400 parts per million

In June 2016, the Baring Head monthly reading of atmospheric carbon dioxide concentrations officially exceeded 400 parts per million (NIWA, 2016). While 400 parts per million is not considered to be any kind of tipping point, it was a symbolic threshold or benchmark – a value that we will never again dip below in our lifetimes. It was also a tangible value to stay below in order to limit global temperature increases and other climate change impacts (see Climate risks: avoiding dangerous climate change).

Scientists at the Stockholm Resilience Centre have made a case for a safe planetary boundary of 350 parts per million of atmospheric carbon dioxide concentrations, with an uncertainty zone of 350–450 parts per million. According to their study, the notion of a planetary boundary for climate change defines a safe operating space in which human societies can develop and thrive (Steffen et al, 2015) – a boundary we have already breached.

 

New Zealand’s carbon stocks

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From 2006 to 2015, there was about twice as much deforestation (120,115 hectares) as afforestation (64,207 hectares).

See Environmental indicators Te taiao Aotearoa: Carbon stocks in forests

Our native and exotic forests absorb carbon dioxide from the atmosphere through photosynthesis and store the carbon as biomass in their timber, roots, and the soil. The amount of carbon stored in living and dead forest biomass (including trunk, roots, branches, deadwood, and litter) and soil makes up a forest’s carbon stocks.

By removing carbon dioxide from the atmosphere, forests help us meet our net emissions reduction commitments. However, this is only effective if the forest area increases to match our increasing emissions. Almost every year since 1990, additional land around New Zealand has been planted in new forests, but this has not been enough to balance the amount of deforestation that has taken place over the same timeframe. From 2006 to 2015, there was about twice as much deforestation (120,115 hectares) as afforestation (64,207 hectares).

Pastures and cropland also store carbon, but it has been difficult to demonstrate clear changes in this storage over time.

Increasing carbon stocks in forests offset greenhouse gas emissions from other sources


Our native forests store about 1.706
billion tonnes of carbon. (Photo: Ministry 

for the Environment)

 

Net greenhouse gas emissions are calculated by offsetting the amount of carbon stored in growing forests against our greenhouse gas emissions.

From 1990 to 2015, our growing forests removed an average of 8.5 million tonnes of carbon from the atmosphere each year – about three times the amount of carbon dioxide emitted by on-road vehicles countrywide (Ministry for the Environment, 2017a).

Our native forests, both mature and regenerating, are predominantly slow growing. Mature native forests store the largest amount of carbon, about 1.706 billion tonnes, because they cover the largest area (almost 6.6 million hectares, about 24 percent of our land area). However, some native trees take many decades to reach full maturity. These carbon stocks are also slow to reach their full potential, so contribute little to offset greenhouse gas emissions from other sources.

By comparison, exotic forests (such as pine), which are planted as wood supply or for erosion control, are generally fast growing, and every year since 1990, additional land has been planted in new forests. There are approximately 2 million hectares of exotic forest around the country. Our exotic forests planted for wood production store just under half as much carbon per hectare as our mature native forests.

Total carbon stored in exotic forests fluctuates over decades as forests grow from seedlings to mature trees and then are harvested and replanted. In 2015, our exotic forests planted for wood production stored about one-sixth the amount of carbon stored in our mature native forests. Many of these exotic forests are nearing maturity and are likely to be harvested soon, which will release carbon back into the atmosphere and will affect efforts to meet our emission-reduction targets.

Deforestation

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About 169,000 hectares of land around the country have been converted from forest to other land use since 2000 – an area almost the size of Stewart Island.

See Environmental indicators Te taiao Aotearoa: Carbon stocks in forests

Deforestation is when a forest is cleared and the land is used for another purpose. Logging managed forest land does not count as deforestation if the land is replanted and maintained as forest land. However, if the managed forest land is logged and converted to another land use, it is counted as a deforested area.

Figure 7 shows the proportion of land deforested from 2008 to 2014 in different regions of New Zealand. About 169,000 hectares of land around New Zealand have been converted from forest to other land use since 2000 – an area almost the size of Stewart Island. In the period 2000–2015, afforestation has been about 10 percent higher than deforestation because of intensive planting in the early years. However, in the last 10 years of that period, deforestation has been nearly twice as high as afforestation.

Figure 7

This graph shows gross percent of land deforested, by territorial authority area, 2008-2014. Visit the MfE data service for the full breakdown of the data.

For more detail on deforestation see the Parliamentary Commissioner for the Environment report Water quality in New Zealand: Land use and nutrient pollution.