Climate change

Greenhouse gases and the greenhouse effect

Greenhouses gases and the 'greenhouse effect' are an essential part of the balance which creates the Earth's unique atmosphere within our solar system.

While other planets such as Venus have scorching temperatures, or freeze - like Neptune - Earth's temperatures are largely temperate. This is due to our atmosphere, the thin layer of gases cloaking our planet, and the distance of the Earth's orbit from the sun.

This balance, which warms Earth but prevents it from becoming too warm, is often referred to as the 'greenhouse effect'1 - because it works much like a greenhouse.

Solar radiation from the sun constantly strikes the Earth's atmosphere, mostly in the form of visible, ultraviolet and infrared light. About 30 per cent of this is reflected immediately back out to space while the rest is absorbed by oceans, land and atmosphere then released as infrared thermal radiation (or heat), passing out of the atmosphere and into space.

Carbon dioxide 2 (CO2) has always been part of this delicate balance, trapping heat in the atmosphere. For hundreds of thousands of years, the concentrations stayed between 200 and 300 parts per million. However, since the industrial revolution 3, humans have burned huge amounts of fossil fuels - such as coal, oil and petrol. These contain carbon, and when they are burnt this combines with oxygen to form CO2.

This, alongside other human activities, from farming to deforestation, has greatly increased concentrations of greenhouse gases, particularly CO2, disrupting that atmospheric balance. There is estimated to be at least 30 per cent more CO2 in our atmosphere than 150 years ago.

These greenhouse gaseous compounds absorb infrared radiation - trapping and holding heat in the atmosphere, ultimately leading to global warming.

As well as fossil fuels, other activities contribute to increased greenhouse gases.

The United States Environmental Protection Agency (USEPA 4), cites the key greenhouse gases emitted by human activities, as:

  • CO2 - from fossil fuels such as coal and from deforestation
  • Methane - through agricultural activities, waste management, energy use and burning of biomass - like wood
  • Fluorinated gases - industrial processes, refrigeration, and use of a variety of consumer products contribute to emissions of F-gases, which include hydrofluorocarbons, perfluorocarbons, and sulphur hexafluoride (SF6)

For more information click here.

It's almost universally acknowledged that if greenhouse gas emissions continue unchecked, it will cause climate change, rising sea levels and extreme weather events. In response, there is an international movement via the UN to try to mitigate impacts through policies that reduce the atmospheric concentrations of greenhouse gases.

Coal is a particular focus of this because it has the highest carbon content of any fossil fuel - and is more emissions intensive per unit of industrial output than any other source. Internationally, some governments and companies are developing carbon capture and storage technologies to capture, transport and store CO2 emissions underground. (Link to article on alternative technologies).

More information about coal can be found here.

In New Zealand the main sources of CO2 are motor vehicles, electricity generation, and the petrochemical, steel, and dairy industries.

Currently, CO2 emissions in the northern hemisphere are higher than those in the southern - however, there has been a dramatic rise in the last decade.

According to New Zealand's Ministry for the Environment's Greenhouse Gas Directory, New Zealand's gross emissions increased by 1 percent from 2013 to 2014.

Agriculture (49 per cent) and energy, including transport (40 per cent) sectors were the two largest contributors. Net emissions from land use, land use change and the forestry sector increased by 2.5 per cent.

Overall, from 1990 to 2014 gross emissions 5 in New Zealand increased by 23.2 per cent. Key drivers of this were:

  • CO2 emissions from road transport, the chemical industry and food processing
  • Methane emissions from livestock digestive systems
  • Nitrous oxide emissions associated with agricultural soils
  • Fluorinated gases released from industrial, and household refrigeration and air conditioning systems

In New Zealand, coal is mainly used in electricity generation, steel making, cement and lime making, food processing, hothouse horticulture, other industrial processing such as wood, wool and leather, and breweries. In the South Island, where there is no natural gas, coal is also used to heat facilities such as educational establishments, hospitals, hotels, offices and swimming pools. (Link to article on the NZ coal story)

In the mining of coal, emissions are released from the use of diesel in mining operations, and from "fugitive methane" released into the air from the coal during opencast or underground mining.

New Zealand has 18 coal mines producing three to four million tonnes a year, around half of which is exported. It is estimated that New Zealand's coal sector, both producers and users, account for about 7% of this country's greenhouse gas emissions. 

Some other greenhouse gases are produced by industrial facilities - such as aluminium smelting 6 - which produces a quantity of fluoride waste, perfluorocarbons and hydrogen fluoride as gases. Perfluorocarbons are powerful greenhouse gases with a long lifetime.

Since the mid-1990s, Tiwai Point owner, New Zealand Aluminium Smelters Ltd, has reduced its greenhouse gas emissions per tonne by almost 60%.

Widespread deforestation 7 due to modern agriculture is also a cause of CO2 build-up. Trees absorb CO2 from the atmosphere, store the carbon in trunks branches and roots, and also release oxygen. When forests are cut this is released into the atmosphere as CO2 through burning or rotting wood.

On the subject of agricultural emissions, learn more from Landcare Research 8.



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