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Climate Change and its Impact on Agriculture and Forestry

This is the second document in a series explaining international efforts to address climate change, New Zealand's response and the implications for agriculture and forestry.

What is Climate Change?

Climate patterns vary within natural cycles and are affected by natural events, such as volcanic eruptions and weather patterns such as La Niña and El Niño. However, in recent decades scientists have been suggesting that human activities that release certain gases into the atmosphere are altering the Earth's climate beyond what would be expected as a result of natural cycles. The term "climate change" refers to projected changes in the Earth's climate that are expected to occur because of human activities.

The Greenhouse Effect

The Greenhouse Effect is the natural phenomenon that warms the Earth, enabling it to support life. The sun's warmth passes easily through the blanket of gases around the Earth to reach the Earth's surface. However, instead of this heat being lost back to space when it is reflected by the Earth's surface, certain gases in the atmosphere (called greenhouse gases) block this heat. Greenhouse gases are a natural part of the atmosphere and without them we could not live on Earth. However, the problem we now face is that human actions, particularly the burning of fossil fuels, are increasing the concentration of these gases. This is believed to be raising the Earth's temperature, creating the prospect of global climate change. This is the Enhanced Greenhouse Effect.

What are Greenhouse Gases?

Water vapour is the most important greenhouse gas, but human activities have little direct impact on the amount in the atmosphere. Humans have most impact on levels of carbon dioxide, methane and nitrous oxide. Also making a relatively small contribution to climate change are various artificial chemicals such as halocarbons.

Carbon Dioxide (C0₂)

On a global scale C0₂ makes the biggest contribution to global warming (about 64%). The C0₂ concentration in the atmosphere is now about 30% higher than 200 years ago. If it continues to increase at the same rate it could nearly double by the year 2035. Burning of oil, coal and natural gas and the clearing and burning of vegetation are the main causes of the increased levels of this gas.

Methane (CH₄)

Methane makes the next biggest contribution to global warming - some 20% of the total. In New Zealand, however, it is our major greenhouse gas. The concentration of CH₄ in the atmosphere has risen by about 145% in the last 200 years. The digestive processes of ruminant animals (e.g. cattle, sheep, goats, deer), rice cultivation, venting of natural gas and waste decomposition in landfills are some of the major sources of CH₄ emissions.

Nitrous Oxide (N₂0)

0Burning vegetation, industrial emissions and the effects of agriculture on soil are the major sources of nitrous oxide. Nitrous oxide levels in the atmosphere are estimated to have increased by 15% in the last two hundred years mainly due to more intensive agricultural practices. In New Zealand, the major sources are the effects of fertiliser applications, leguminous plants and animal waste on soil processes. The biological processes involved in nitrous oxide emissions from soil are not well understood and consequently there is considerable uncertainty with estimations of agricultural nitrous oxide emissions.

Halocarbons

Halocarbons of greenhouse significance include perfluorocarbons (PFCs), emitted primarily during aluminium production, and hydrofluorocarbons (HFCs) used as replacements for ozone-depleting substances.

How might the Climate Change?

A number of possible impacts of climate change have been identified. The main impacts are predicted to be temperature increases, sea level rises, changes to rainfall patterns and increased variability of weather events.

Temperature increases

• The Earth's mean surface temperature is predicted to increase by about 2⁰C by the year 2100 if emissions continue to increase at current rates. The most optimistic scenario, according to the International Panel on Climate Change (IPCC) is for an average global increase of about 1⁰C in the next 100 years. The most pessimistic is for an average global increase of about 3.5⁰C. Temperature rises are expected to be greater towards the poles than near the equator.
  

• Climate models for the Australia-New Zealand region predict average temperatures to rise between 0.7⁰C and 3.1⁰C over the next 100 years.

Sea Level Rises

• Global mean sea level is estimated to have risen 10-25cm over the last 100 years.|
  

• In the next 100 years the average sea level is projected to be about 50cm higher than today, due to the oceans warming and expanding and increased melting rates of glaciers and ice caps (however, there is considerable uncertainty in this projection).
  

• The rate of sea level rise in New Zealand would not necessarily be the same as the global average.
  

• Rising sea levels would pose particularly severe threats to island nations comprising low level atolls such as the Tokelau Islands.
  

• Some low lying coastal areas in Northland, Bay of Plenty, and the east coasts of both islands are exposed to the prospect of coastal erosion, particularly if exacerbated by storm

Rainfall

• Globally, rainfall is expected to increase in some areas and decrease in others. Changes are likely to be highly localised.
  

• In New Zealand, climate models predict a decrease in year round rainfall on the east coast of the South Island and in winter rainfall on the east coast of the North Island. Elsewhere, rainfall is predicted to increase.

Increased Variability of Weather Events

• The frequency and intensity of extreme weather events such as cyclones, floods, droughts and heatwaves may change. However, climate change models can st~l not predict how. Rising ocean surface temperatures for example, are expected to affect storm and cyclone development.

Has Climate Change Already Begun?

There has been a significant shift in the New Zealand climate over the last 20 years. Annual temperatures in the central and eastern parts of the North Island have risen by up to 0.25⁰C in the last twenty years. Recent trends indicate more droughts in the north and east of the North Island, more damaging floods in the west and south of the South Island, fewer frosts nation wide, night time temperatures continuing to rise and stronger westerly winds over southern and central New Zealand. 1998 was the hottest year on record, with an average temperature 0.8⁰C above normal.

It is not possible to say at this point whether these changes in climate patterns are linked to human activities or naturally occurring cyclical fluctuations in the climate. However, the pattern of temperature change, globally and nationally, over the past few decades is very consistent with the predicted effects of global warming. While many uncertainties remain, scientists believe that "the balance of evidence suggest a discernible human influence on global climate". Ref. Intergovernmental Panel on Climate Change (IPCC); Summary for Policy Makers, Working Group 1, Chapter 4.

Are El Niño and La Niña phases linked to global warming?

Recent analysis suggests that rising global temperatures may be linked to stronger and more frequent El Niño episodes. In the past twenty years, there have been significantly more El Niño episodes than in the 20 years before that. El Niños are characterised by enhanced westerly winds, with a high risk of drought on the east coast of both islands. La Niña episodes are characterised by more northerly and easterly winds. The southern part of the South Island is prone to drier than normal conditions while temperatures are above average in the north and west of the North Island.

How may climate change impact on agriculture and forestry?

Climate change is likely to have both positive and negative effects on agricultural and forestry production Systems in New Zealand. Climate change can be expected to increase production risks and require changes in the way farmers and growers select and manage their enterprises in the future.

Some of the major risks include:

• Loss of productivity, loss of income and associated social stresses.
  

• Transitional costs of shifting from one land use activity to another more suited to a new climate.
  

• Increased frequency of extreme weather events (e.g. more droughts, high winds and localised flooding) leading to business disruption and infrastructure damage.
  

• Increased pressure on water resources.
  

• Increased pest and disease problems (a significant risk for the horticulture sector), due to increased activity of organisms already present and the increased risk of any new species entering the country being able to survive and reproduce.

Some of the potential benefits include:

• The expansion of existing crops into new production areas, for example Pinus radiata or kiwifruit or maize, may be able to be grown in areas not currently planted due to climatic limitations.
  

• The prospect of being able to introduce new crops (and crop related industries) not currently present in New Zealand.
  

• Rising temperatures and C0₂ levels may assist the growth of pastoral plants and forestry species.
  

• The opportunity to supply products into export markets facing more adverse impacts on production than New Zealand.

Contact for Enquiries

MAF Information Services
Pastoral House
25 The Terrace
PO Box 2526
Wellington, NEW ZEALAND

Fax: +64 4 894 0721
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