Frequently Asked Questions
Global Change
- What is the greenhouse effect?
The greenhouse effect is a natural process that helps regulate the Earth's temperature. The greenhouse effect is the result of heat absorption by gases in the atmosphere (greenhouse gases) that 'trap' heat in the lower atmosphere. Some of this trapped heat is radiated back to Earth, warming it. Without the greenhouse effect, the temperature of the Earth would be about -18°C instead of its present 14°C.
- If the greenhouse effect is a natural process, why are we worried?
The problem is that human activity is increasing the concentration of greenhouse gases in the atmosphere. This is enhancing the greenhouse effect, so the Earth is warming faster than it should.
- Which gases are greenhouse gases?
Water vapour is the most abundant greenhouse gas, followed by carbon dioxide. Other greenhouse gases include methane, nitrous oxide, and fluorocarbons.
- Is our climate really changing?
Yes. Global surface temperatures have increased by about 0.6°C since the late-19th century, and about 0.2-0.3°C over the past 25 years. We can see environmental effects of global warming in, for example, changing patterns of snow cover, and decreases in the length of glaciers and Arctic sea ice. A dramatic global warming, at least partly associated with the El Niño phenomenon, took place in 1998.There is clear evidence of changes in climate variability or extremes at regional scales. However, at a global scale sustained trends are less obvious. In recent years, drought or wet spells accompanying El Niño episodes have been more intense. Some areas have experienced increased rainfall, and extra-tropical cyclone activity appears to have increased in the Northern Hemisphere, but decreased in the Southern Hemisphere, over the past 50 years.
- Is our sea level rising?
Over the past 100 years the global mean sea level has been rising at an average rate of 1 to 2 mm per year. This is significantly higher than the rate averaged over the last several thousand years.
- Are El Niños related to Global Warming?
El Niños have been present for hundreds of years. Although El Niños are not caused by global warming, warmer global sea surface temperatures may enhance the El Niño phenomenon. El Niños have been more frequent and intense in recent decades, and a change in El Niño - Southern Oscillations (more frequent and persistent El Niño episodes rather than the cool La Niñas) that occurred in the mid-1970s has persisted.
- Can't observed changes in climate be explained by natural variability?
Earth's position and orientation relative to the sun (its orbit) varies slightly in predictable cycles (called Milankovitch cycles). These are believed to be the cause of ice-ages. Although Milankovitch cycles are important in explaining ice-ages and long-term changes in the climate, they are unlikely to impact significantly at decade or century timescales. In predicting climate change in the 21st century, changes in the Earth's orbit will be far less important than rises in temperature resulting from increased levels of greenhouse gases in the atmosphere.
Kyoto Protocol
- What is the Kyoto Protocol?
The Kyoto Protocol was established under the United Nations Framework Convention on Climate Change (UNFCCC). It is the first legally binding international agreement aimed at slowing and eventually stopping global warming. Over 80 countries have signed the Kyoto Protocol, indicating their intention to consider adopting legally-bound greenhouse gas emissions targets. However, the Protocol will come into force only if 55 countries ratify it.
- New Zealand has ratified the Kyoto Protocol. What does this mean?
New Zealand's ratification of the Kyoto Protocol signals the Government's commitment to reduce our emissions of greenhouse gases. Under the Protocol, we are legally bound to reduce our emissions over the first commitment period (2008-2012) to 1990 levels on average, or to take responsibility for emissions over these levels. "Taking responsibility" means offsetting excess emissions by, for example, using sink credits from Kyoto forests or trading emissions units on the international market. The Government is looking at policy options to encourage reduction of greenhouse gas emissions, for example specific projects, and negotiated greenhouse agreements (NGAs) between business and the Government.
- What is a greenhouse gas sink?
A sink is any natural or man-made system that absorbs greenhouse gases from the air.
Because sinks remove greenhouse gases, the Kyoto Protocol allows countries to get credit for them (to offset emissions). One sink credit will be allocated for every tonne of carbon dioxide equivalent absorbed after 1 January 2008. Sink credits are also referred to as emission units devised from sink activities.
Similarly, a carbon sink is any system that absorbs carbon dioxide from the atmosphere.
Afforestation and Reforestation
- What is a "Kyoto forest"?
Kyoto forest is forest that can be used in calculating sink credits to offset greenhouse gas emissions. A forest is deemed to be Kyoto forest if it has been established since 1 January 1990 on land that was previously unforested. Carbon released on deforestation or harvesting of Kyoto forests must be taken into account in inventories.
- How much carbon is stored in perpetuity in indigenous forest versus a pine forest that is harvested every 25 years?
Average above-ground C for NZ forests (from the National Vegetation Survey data) = 143 Mg/ha. (Hall et al. 2001). This data represents a composite figure for all forest types. Forests are assumed to be at equilibrium but could be in the process of succession, or in decline following canopy disturbance by environment or animals.Hall G.M.J. (2001). Mitigating an organisation's future net carbon emissions by native forest restoration. Ecological Applications 11, 1622-1633. (Copyright by the Ecological Society of America). Maclaren J.P. (1996). Plantation forestry: its role as a carbon sink. In: Greenhouse: Coping with Climate Change, (eds W.J. Bouma, G.I. Pearman, M.R. Manning), CSIRO Publishing, Collingwood.Maclaren's (1996) figures for pine are on average 112 Mg/ha (above-ground) in perpetuity, assuming a 25-30 year harvest cycle. This does not take into account fossil fuel use to process the wood or the anaerobic decay of wood in landfills to produce methane.
- If the pine forest is never harvested how much carbon does it store?
Maximum above-ground biomass predicted using the LINKNZ model (Hall et al. 2001) is about 550 Mg/ha after 80 years.Hall G.M.J. (2001). Mitigating an organisation's future net carbon emissions by native forest restoration. Ecological Applications 11, 1622-1633. (Copyright by the Ecological Society of America).
- If the pine forest is never harvested what will happen to it once the old trees die?
If we assume that this gives way to indigenous forest LINKNZ predicts an equilibrium value for above-ground biomass of about 400 Mg/ha. This is about 20% less than the maximum value obtained in an indigenous succession to podocarps alone.
- If I have a mature indigenous forest what difference will harvesting a couple of big trees make? Won't this just promote greater growth of surrounding trees?
The answer to this is largely unknown. It seems to depend on the site and the species concerned. Some species of beech exhibit compensatory growth when several trees are harvested but others die back when this kind of canopy opening is created.