What is
climate
change?

Published: July 17, 2019

Tagged with:

  • Explanation
  • Agricultural emissions
  • Climate change
  • Emissions reduction
  • Greenhouse gases

Earth is heating up due to rapidly increasing concentrations of greenhouse gases in the atmosphere. Significant changes to the climate are occurring as a result, which affect our natural environment, primary sector, infrastructure and built environment, as well as human health.

What is climate change?

Transcript

Duration: 2:42

GAVIN
Kia ora. We’re here to talk about climate change – how it works, and how it relates on-farm.

CARRIE
We’ll also reveal New Zealand’s biggest contributor to climate change. It might not be what you think, and it’s rather close to home.

COW 1
[Belch]

COW 2
[Belch]

COW 3
[Is she looking at us?]

CARRIE
Our atmosphere is a magnificent cocktail of gases, water vapour and particles that constantly mix and mingle. It gives us our oxygen, protects us from radiation from the sun, and controls our weather. It’s a delicate balance, and all life depends on it.

GAVIN
But we’re doing things down here which are really upsetting the balance up there. Human activities are rapidly increasing the concentration of greenhouse gases in the atmosphere. They’re called greenhouse gases because they trap the heat and warm the planet. The main greenhouse gases that we produce are carbon dioxide, nitrous oxide and methane. Globally, carbon dioxide is the most important because it stays in the atmosphere a very long time.

CARRIE
Here’s what’s going on.

GAVIN
Incoming solar radiation warms up the surface of the Earth. The Earth’s surface then sends this heat back through the atmosphere and most of it goes out into space. But some of this heat is trapped by greenhouse gases, and this extra heat warms up the atmosphere.

So, the more greenhouse gases we emit into our atmosphere, the more it’ll warm up and affect our climate.

CARRIE
And it’s already having a big impact. Earth’s temperature has warmed by about one degree Celsius since humans started using coal, oil and other fossil fuels. Globally, 18 of the hottest 19 years on record have occurred since the year 2000.

Here in New Zealand, temperatures are about one degree hotter than they were a century ago. We’re seeing more extreme weather and that’s before we talk about rising sea levels, melting glaciers and polar ice. 

SHEEP 1
Indeed, the evidence is compelling.

CARRIE
As our climate in New Zealand changes, it might not be possible to farm in the same ways or the same places as we do now. A couple of degrees of warming might not seem like much, but it has a big impact on crop and pasture growth, and on pests and diseases. More extreme weather also creates bigger problems.

GAVIN
Now it might surprise you to learn that New Zealand’s biggest current contribution to this isn’t carbon dioxide at all.

CARRIE
Nope. It’s methane from animals.

COW 1
[Belch]

COW 2
What the?

CARRIE
You can find out more about how methane affects climate change in our next video.

Produced by the New Zealand Agricultural Greenhouse Gas Research Centre. Funded by the New Zealand Government

What are greenhouse gases?

Earth’s atmosphere is a magnificent cocktail of gases, water vapour and particles that constantly mix and mingle. It gives us our oxygen, protects us from radiation from the sun, and controls our weather. It’s a delicate balance, and all life depends on it.

A number of the gases in the atmosphere act like a blanket around the Earth, trapping warmth from the sun. For this reason, we call them greenhouse gases.

Greenhouse gases exist naturally in low concentrations. Without them, too much heat would escape, and the surface of the planet would freeze.

But human activities are rapidly increasing the amount of these gases in the atmosphere, which is causing the temperature to increase and the climate to change.

The greenhouse gas effect in the atmosphere is illustrated in this diagram.

greenhouse effect explained infographic
Title: The greenhouse effect explained

Left: Naturally occurring greenhouse gases — carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O) — normally trap some of the sun’s heat, keeping the planet from freezing.
Right: Human activities, such as the burning of fossil fuels, are increasing greenhouse gas levels, leading to an enhanced greenhouse effect. The result is global warming and unprecedented rates of climate change. Image: Will Elder, U.S. National Park Service

This increase started in the middle of the 19th century when industrial innovations, like the widespread use of coal, oil and gas to power our cities and cars, transformed the way we live. At the same time, forests were cleared to make way for cities and farms to feed the rapidly growing global population.

Since then, industry, agriculture and transportation have continued to increase the level of greenhouse gases in the atmosphere, causing Earth to heat up at a rate unprecedented in recent history.

global average temperature 1880 2019
Title: Global average temperature 1880–2019

Reference: GISTEMP Team, 2019: GISS Surface Temperature Analysis (GISTEMP). NASA Goddard Institute for Space Studies. Dataset accessed 12 June 2019, at https://data.giss.nasa.gov/gistemp/. Lenssen, N., G. Schmidt, J. Hansen, M. Menne, A. Persin, R. Ruedy, and D. Zyss, 2019: Improvements in the uncertainty model in the Goddard Institute for Space Studies Surface Temperature (GISTEMP) analysis. J. Geophys. Res. Atmos., in press, doi:10.1029/2018JD029522.

Many gases created by human activities act as greenhouse gases, but the three most important from a New Zealand perspective are:

  • Carbon dioxide (CO2): Carbon dioxide enters the atmosphere when fossil fuels (oil, natural gas and coal), solid waste, trees and wood products burn, and during other chemical reactions such as manufacturing cement. Carbon dioxide is removed from the atmosphere by growing plants, which absorb and store it in their tissue. It gets released again when plants decay as part of the biological carbon cycle. Carbon dioxide from fossil fuels makes up 44% of New Zealand’s gross annual greenhouse gas emissions.
  • Methane (CH4): Methane is emitted during the extraction and transportation of coal, natural gas and oil. Methane emissions also come from livestock and agricultural practices such as growing rice, and by the decay of organic waste in landfills. It makes up 43% of New Zealand’s gross emissions, mainly from cattle and sheep.
  • Nitrous oxide (N2O): Nitrous oxide is emitted during agricultural and industrial activities, and when fossil fuels and solid waste burn. It makes up 12% of New Zealand’s gross emissions.

How do we know that the climate is changing?

The scientific evidence is clear.

Globally:

To read more about the evidence for climate change and watch time lapse videos of the increase in global temperatures, melting ice caps and rising sea levels, have a look at this NASA resource or the most recent reports by the Intergovernmental Panel on Climate Change here and here.

Here in New Zealand, temperatures are about 1°C hotter than they were a century ago, with three of the hottest years on record occurring since 2014. Effects are already being felt in our land, freshwater and marine environments:

These are set to continue.

As our climate changes, it might not be possible to farm in the same way or the same places as we can now. A couple of degrees of warming might not seem much, but it can have a big effect on crop and pasture growth, and on pests and diseases. Here are some predictions:

  • Many places will see more than 80 days per year above 25°C by 2100, which will have a significant impact on ryegrass growth (which prefers temperatures in the range of 5–18°C) and animal performance.
  • Annual average rainfall is expected to decrease in the north-eastern South Island and northern and eastern North Island and increase in other parts of New Zealand.
  • Farmers in dry areas can expect up to 10% more drought days by 2040.

To read more about current and future impacts of climate change in New Zealand, see:

What is New Zealand’s contribution to climate change?

New Zealand is currently responsible for about 1% (or 0.01°C) of the total global warming (around 1°C) that has occurred since pre-industrial times, when we include historical emissions from deforestation by early settlers. Read more about this in a report from the Parliamentary Commissioner from the Environment.

While that is small in absolute terms, it is more than 15 times greater than our share of the global population and more than five times greater than our share of the global land area.

calculated contribution to global average temperature change
Title: Calculated contribution to global average temperature change from New Zealand’s emissions to date of carbon dioxide from land-use change and from fossil fuel use, nitrous oxide, and biogenic methane.

Our greenhouse gas profile sets us apart from many other countries.

Globally, carbon dioxide is the main greenhouse gas, but nearly half New Zealand’s reported annual emissions come from livestock production, and they have caused more warming to date than emissions from fossil fuels.

This reflects our strong primary production base and use of renewable energy to generate most of our electricity.

This information is reported annually in New Zealand’s Greenhouse Gas Inventory.

NZ greenhouse emissions, by industry, as percentages
Title: New Zealand's greenhouse gas emissions (percentages)

Fugitive emissions are from the leakage, burning and controlled release of gases in oil and gas operations as well as escaping gases from coal mining and geothermal operations. Agricultural methane is mainly from livestock digestive systems and nitrous oxide is mainly from manure on soil.

Note: Percentages in the graph may not add up to 100 due to rounding.

What are New Zealand’s climate change commitments?

New Zealand currently has three greenhouse gas emissions reduction targets:

  • By 2020 – reduce emissions to 5% below 1990 levels
  • By 2030 – reduce emissions to 30% below 2005 levels
  • By 2050 – reduce emissions to 50% below 1990 levels

These targets apply across the economy – they do not specify reductions for individual sectors or gases. Read more from the Ministry for the Environment about these commitments here.

The Government has proposed amendments to existing climate change legislation to set a new emissions reduction target by 2050. The proposed legislation would set a net zero emissions target for the long-lived greenhouse gases (carbon dioxide and nitrous oxide) and a separate, less stringent, target for biogenic methane, given it behaves differently in the atmosphere. Read more about this Zero Carbon Bill.

At present, there is no dedicated policy to reduce greenhouse gas emissions from agriculture. All other sectors of the economy are included in New Zealand’s Emissions Trading Scheme (ETS), which has recently been amended to make it more effective. More information on the ETS can be found here.

New Zealand also has programmes in place to support afforestation under the One Billion Trees Programme, and supports a range of other climate change initiatives including energy efficiency and conservation and establishment of a Green Investment Fund.

The Government has established an Interim Climate Change Committee to provide independent evidence and analysis of two key issues for climate change policy in New Zealand: agriculture and electricity. The Committee submitted its final reports, with recommendations, to the Government on 30 April 2019. The Government is considering this advice before releasing the reports and its response. Read more about the work of the Committee here.

Published: July 17, 2019