What is climate change and why is it happening?

Human induced climate change is one of the widest-reaching hazards facing New Zealand.

It significantly influences how the risks from many hazards are likely to change in the future. In essence, climate change describes how the average weather patterns over New Zealand, and their extremes, will change from their current state. This change is being predicted as a result of the "global warming" of the Earth, caused by the emission of greenhouse gases.

Causes of Climate Change

On the issue of global warming and its causes, the Intergovernmental Panel on Climate Change (IPCC) stated in its most recent assessment report that "Most of the observed increase in global average temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations."This statement was based on a vast array of evidence from observations, as well as our understanding of the physics of the atmosphere, ocean and land.

Globally, the biggest contribution to greenhouse gases is from carbon dioxide, which is emitted when fossil fuels are burnt for their energy. In New Zealand the emission of methane from agriculture is also a significant contribution to our local emissions.

Potential consequences of Climate Change

Some of the key impacts of climate change for New Zealand are:

  • Sea level rise - Sea levels around New Zealand are expected to rise due to the ocean expanding as it warms, as well as the melting of glaciers. Sea level rise around New Zealand is likely to be similar to global projections. This rise depends on the amount of warming, and critically on the response of glaciers in Greenland and Antarctica.
  • Heavy rainfall and flooding - A warmer atmosphere can hold more moisture (about 7% more for every 1°C increase in temperature). Modelling work suggests that for New Zealand all rainfall extremes can be expected to increase by about this amount. On top of this, local atmospheric circulation changes can further increase or decrease rainfall extremes.
  • Drought – Droughts are projected to become more frequent and more intense under climate change. Droughts represent a significant cost to the agricultural sector of the New Zealand economy.
  • Strong winds – Climate models suggest that the frequency of extreme winds over New Zealand is likely to increase in almost all areas in winter, and decrease in summer. Increases in strong winds may mean that coastal regions exposed to the prevailing winds may be subject to an increase in the frequency of heavy swells, which would add to the effects of higher sea levels
  • Daily temperature extremes and frosts – In addition to changes in mean temperature, daily temperature extremes will also vary with regional warming. A large decrease in the number of frost days is projected for the central North Island and in the South Island as the 21st Century progresses. An increase in the number of days above 25°C is also expected, particularly at already warm northern locations. High temperature extremes are known to have impacts on human health as well as economic costs.
  • Biological systems - Higher temperatures could favour conditions for the increased spread of exotic diseases and pests, affecting both fauna and flora.

Climate Change research at NIWA

To identify likely future climate changes across New Zealand, projected changes from global climate models are downscaled by NIWA scientists to a level that is useful for studying local impacts. These global climate models have been driven by a range of emissions scenarios that represent possible futures for the Earth. The downscaling for New Zealand is done using both statistical techniques that rely on historical relationships, as well as a regional climate model. The latter includes all the physical equations that are necessary to describe how the atmosphere behaves, and requires the use of NIWA's supercomputer, Fitzroy, to solve these complicated equations.

The output from both these techniques is then used as input to other models e.g. river flow models, crop models which simulate plant growth, or even animal population models. Research is also undertaken to analyse the hazards that these changes represent. To learn more about how NIWA makes predictions about the impact of climate change see our page on Climate change scenarios for New Zealand.

Climate change scenarios for New Zealand

Current NIWA research projects

Regional Modelling of New Zealand Climate - This programme aims to better quantify climate changes over New Zealand, and to encourage better use of climate change scenario information in strategic planning. Detailed projections and data sets of future climate change are produced from regional climate models and from statistically downscaled global models. These projections can then be used to drive other environmental models that address issues relevant to water resources, tourism, and urban and coastal infrastructure.

Regional Modelling of New Zealand Climate

Risk of drought under climate change - Of all of the threats posed to New Zealand by climate change, drought is the one which could have the largest effect on New Zealand's economy. This project has significantly advanced previous estimates of how drought severity and frequency are likely to change as global warming effects New Zealand.

Risk of drought under climate change 

Climate change and urban impacts - This research programme recognises that some of the greatest impacts of climate change will occur in the built-up urban environment. The programme aims to help central and local government identify opportunities for adaptation by using a science-based risk assessment process to reduce the impacts of climate change on urban infrastructure.

Climate change and urban impacts

Impacts of climate change on river flows and floods - This project will demonstrate how to use the latest global climate forecasts to predict changes in river flows in New Zealand, including changes in size or frequency of future floods.

Impacts of climate change on river flows and floods

Analysis by NIWA suggests that urban water managers may need to prepare for more – and more challenging – dry spells as our climate changes. [Photo: Dave Allen]
Projected surface temperature changes for the late 21st century (2090-2099) from the IPCC Fourth Assessment Report. You can see the original with a more detail explanation on the IPCC website.