Forestry Insights

The Earth’s climate has been in a continual state of change for billions of years and during the comparatively brief period of time represented by human history there have been well-chronicled climatic fluctuations.  For some years during the 17th century European winters were so cold that major rivers froze – the River Thames in London was sometimes frozen so solidly that fairs and markets were held on the ice.

However, there is now international scientific agreement that the current trend of steadily rising temperatures – about 0.5 degrees Celsius over the past 100 years – is not part of a long-term cyclical variation. 

• The 1980s and 1990s are the warmest decades on record
• The 10 warmest years (since meteorological records began) have
  occurred during the past 15 years
• The 20th century was the warmest globally during the past 1000 years

The Earth is getting warmer and:

“There is new and stronger evidence that most of the warming observed over the last 50 years is attributable to human activities.”
Intergovernmental Panel on Climate Change (IPCC)

Global warming is being caused by increasing levels of ‘greenhouse gases’ which trap the heat of the sun inside the Earth’s atmosphere.   For tens of thousands of years these gases have provided natural insulation and made life on Earth possible – without any ‘greenhouse effect’, the heat of the sun would escape and temperatures on Earth would drop to around minus 18 degrees Celsius.

Global warming is caused by greenhouse gases which trap the heat of the sun inside the Earth’s atmosphere

However, since the Industrial Revolution – that is during the past 200 years or so – developed countries have produced ever-increasing quantities of greenhouse gases.  This has been largely due to the burning of fuels such as coal, oil and natural gas for transport, energy, heating and air conditioning.  Other human activities, the clearing of land for agriculture and urban development, are also responsible for greenhouse gas emissions.

The main greenhouse gases are:
Water vapour (H_²O)
Carbon dioxide (CO₂)
Methane (CH₄)
Nitrous oxide (N₂O)
Ozone (O₃)
Halocarbons and  (CFCs, HFCs, PFCs, etc.)

Carbon dioxide, methane and nitrogen oxide
are the three main greenhouse gases

Carbon dioxide is the most significant greenhouse gas and it is released when fossil fuels (coal, oil and gas) are burnt.  It is estimated that at least 22 billion tonnes of carbon dioxide are emitted in this way every year.

Concentrations of carbon dioxide in the atmosphere have increased by 31% since 1895.  Before the Industrial Revolution, research scientists have determined that the concentration of carbon dioxide in the atmosphere was about 280 parts per million.  In March 2004, at the Mauna Loa Observatory in Hawaii, scientists took readings of 379 parts per million – this compared with 376 parts per million just one year before.  It is now predicted that the level will exceed 450 parts per million by the middle of the century.

Carbon dioxide levels have increased by 31% since 1895

Methane is a gas which is produced when vegetation is burned, digested or rotted in conditions where there is no, or very little oxygen.  Methane is released by rubbish dumps, compost heaps, septic tanks, rice paddies and by the digestive processes of grazing animals.  Concentrations of methane have increased by 151% since 1895.  It is an important greenhouse gas because it is 20 times more effective at trapping heat than carbon dioxide.

Methane levels have increased by 151% since 1895

Nitrous oxide levels have increased by 17% since 1895. Nitrous oxide is a gas which is naturally emitted from soils and oceans. Human activity contributes to the release of the gas through the cultivation of the soil and the use of nitrogen fertilisers.

Nitrous oxide levels have increased by 17% since 1895

Both methane and nitrous oxide are serious issues for the control of greenhouse gas emissions in New Zealand where agriculture, especially dairy and sheep farming, is the most important economic activity.  According to the latest national inventory, agriculture accounts for 50% of the country’s total emissions and this level is rising.

Agriculture causes 50% of New Zealand's greenhouse gas emissions

By the middle of this century the level of carbon dioxide in the atmosphere will have doubled since the beginning of the Industrial Revolution.  Scientists agree that this will have the effect of increasing Earth’s average surface temperature by 1.4 to 5.8 degrees Celsius.  Temperatures are likely to increase more rapidly over land than over the sea.

The latest reports, from a climate modelling experiment being run on a global scale by United Kingdom researchers at Oxford University, predict that by the mid-century temperatures could be as much as 11 degrees Celsius higher.

The effects of this increase in temperature on the Earth’s climate and the weather patterns experienced in each region are difficult to predict with any accuracy but it is certain that substantial melting of the polar ice caps will lead to a significant rise in sea level that will devastate many highly populated, low lying areas.  One hundred million people live within a metre of mean sea level. 

Ice caps are melting and sea levels are rising

The British Antarctic Survey has shown that the West Antarctic Ice Sheet has already begun to disintegrate and ice is flowing out into the ocean at the rate of 250 cubic kilometres per year.

Meteorological conditions are already thought to be changing with more dramatic fluctuations in seasonal weather being experienced in many parts of the world – devastating storms and floods, blizzards with exceptionally heavy snowfall, protracted droughts in areas that have traditionally relied on predictable rainfall seasons.  Since the beginning of the 1990s there has been increased incidence of droughts in regions of Australia used to getting regular seasonal rainfall.  Devastating wildfires – with massive emissions further increasing the greenhouse effect – have been the all too common consequence.  New Zealand too has experienced marked changes in weather patterns.

Agricultural failure, water shortages, increased disease and the death of the world’s major tropical and sub-tropical forests are likely consequences.  And, in the long term, global warming is going to be a serious threat to the future of all human life on Earth – some of the most alarming reports indicate that substantial areas of land will be made uninhabitable by the end of this century.

Global warming is a threat to human life on Earth

In theory, it is possible that global warming can be slowed by drastically reducing the level of greenhouse gas emissions.  Recognising this, the parties to the United Nations Framework Convention on Climate Change met in Kyoto, Japan in 1997 and agreed on a protocol to reduce greenhouse gas emissions by harnessing the forces of the global marketplace to protect the environment.

A pact to reduce greenhouse gas emissions – but only by 5%

The objective of the protocol is for industrialised countries to reduce greenhouse gas emissions to 5% below 1990 levels before 2012.  There was a major setback when the United States – the world’s largest user of energy and responsible for 36% of carbon emissions – refused to ratify the agreement.  Australia also refused to join.  It had been agreed that the protocol could only proceed if enough countries were on board to account for 55% of global emissions at 1990 levels.  When Russia ratified in late 2004, this quota was reached and the Kyoto Protocol entered into force on February 16, 2005.  The 141 signatory countries are now preparing for the first commitment period which runs from 2008 to 2012 during which time they are legally obliged to meet the emissions reduction targets laid down by the protocol.

The Kyoto Protocol allows nations with emissions targets to trade greenhouse gas allowances so that they can meet their targets at the lowest cost.  This means that countries can buy less expensive emissions permits from countries that have more permits than they need (because they have met their targets and have credits left over).  Structured effectively, emissions trading will provide a powerful economic incentive to cut emissions.

Carbon ‘locked up’ in forests can be used to meet reduction targets

Under the terms of the protocol, carbon that is ‘locked up’ in forests planted since 1990 (on land that was previously unforested) can be measured and evaluated in ‘carbon credits’ which can then be used to help meet national targets either by the sale of these credits on the international market or by directly offsetting emissions which threaten to unbalance a country’s ‘carbon budget’.

While this may provide a financial incentive for the planting of more forests, many environmental groups are opposed to the use of forest generated carbon credits as laid down by the protocol.  It is feared that countries rich in forest credits may be slow to take measures to reduce emissions generated by traffic, power generation and industrial activity.

Many scientists are already describing the protocol as doing “far too little … far too late.”  It has been calculated that if all the signatory countries meet their reductions targets for the rest of the century, it would slow down the process of global warming by just six years.

The Kyoto Protocol could be ‘too little – too late’