Since the industrial revolution of the early 19th century, the concentration of greenhouse gases such as carbon dioxide, methane and nitrous oxide has increased in the atmosphere. They now far exceed pre-industrial levels as determined from ice cores that span thousands of years.
Global increases in atmospheric carbon dioxide concentration are caused primarily by fossil fuel use and land-use change, while increases in methane and nitrous oxide are primarily due to agriculture. This increased concentration of gases traps more of the earth’s warmth than normal, leading to a gradual warming of the atmosphere.
Fluctuations in the ‘natural’ atmospheric system bring about changes in climate (climate variability). However, changes in the climate as a result of increased concentrations of greenhouse gases in the atmosphere are expected to be much greater, and to happen more quickly, than any natural changes in the past 10,000 years.
Most of the increase in global temperatures since the mid-20th century is attributed to increased greenhouse gas concentrations caused by human activity. Human activity also influences other aspects of the climate, such as ocean warming, temperature extremes and wind patterns.
Climate change is expected to have significant impacts on our economy, environment and the way we live – the effects of a warming planet and subsequent changing climate patterns are already becoming evident.
The main features of projected climate change impacts on New Zealand for 2040 and 2090 are shown in this table.
This map of regional climate impacts provides an indication of projected regional impacts of climate change in New Zealand.
New Zealand’s average surface temperature increased by 0.9°C between 1908 and 2006. This increase is consistent with the increase in average global temperature of 0.76°C in the past century. The average minimum temperature has increased by 1.2°C and the maximum has increased by 0.7°C over the same period for New Zealand. Frost frequency has decreased since the 1950s.
These changes suggest that we can no longer rely on using historical climate data to predict our future climate patterns.
Note: The bars represent annual anomalies, that is, the difference in temperature in an individual year compared with the average for the 1980–1999 period. The straight line represents the linear trend in temperature anomaly between 1908 and 2006.
Source: Ministry for the Environment; National Institute of Water and Atmospheric Research.
For the next two decades (to 2030), global increases in temperature of about 0.2°C each decade are projected for a range of expected levels of greenhouse gas emissions. Best estimate projections of global temperature increases by 2100 are between 1.8 and 4°C.
The mid-range projections are that New Zealand temperatures will increase by about 1°C by 2040 and 2°C by 2090, relative to 1990. The annual-average pattern of warming is projected to be fairly uniform over the country, although slightly greater over the North Island than the South Island.
Maps and tables showing projected temperature changes in New Zealand regions for 2040 and 2090 are available below.
One of the greatest impacts of climate change is likely to be on water resources.
An increase in westerly winds is expected to result in more rainfall and flooding in the west, and less rainfall and more droughts in the east and north of the country.
Maps and tables showing projected rainfall changes for New Zealand regions for 2040 and 2090 are available below.
A small shift in the average climate can cause significant changes in the occurrences of extremes (such as heavy rainfall, strong winds, storm surges, drought and very high temperatures). Generally, it is the extreme events that cause damage.
Climate models predict that New Zealand will experience an increased frequency and intensity of extreme weather events, including more droughts in already drought-prone areas, and larger and more frequent floods in regions already vulnerable to flooding.
Climate change is expected to impact on existing drivers of coastal hazards in New Zealand such as tides, storms, waves, swells and coastal sediment supply - with a range of expected consequences on coastal erosion processes, sea-level rise and saltwater intrusion into aquifers.
More information on expected impacts and preparing for coastal change.
The Intergovernmental Panel on Climate Change brought together the most up-to-date knowledge on climate change in its Fourth Assessment Report in 2007.
A number of other helpful resources are available on the climate change website.
Climate change and ozone depletion are accelerated by human activity. Many ozone-depleting gases are also greenhouse gases. By reducing the use of ozone depleting gases, we can both protect the ozone layer and reduce climate change.
At the same time, climate change is likely to accelerate the recovery of the ozone layer, at least outside polar regions. While the earth’s surface is expected to warm in response to increases in greenhouse gases, the stratosphere is expected to cool. Outside polar regions, this combination results in a decrease of the rate of ozone depletion. However, in polar regions, the lower stratospheric temperatures and stronger polar winds could extend the period over which stratospheric clouds are present, which in turn promotes chlorine-caused ozone destruction.
This information has come from:
Last updated: April 2009