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The science behind climate change

The science behind climate change

Updated 7 August 2017 8:23am

What is climate change?

Solar energy enters our atmosphere as shortwave radiation in the form of ultraviolet rays and visible light. The Earth's surface absorbs some of this energy and heats up. The Earth cools down by giving off a different form of energy, longwave infrared radiation. But before all this radiation can escape to space, greenhouse gases in the atmosphere absorb some of it, which makes the atmosphere warmer. As the atmosphere gets warmer, it makes the Earth's surface warmer, too. In the absence of any atmosphere, the upward radiation from the Earth would balance the incoming energy absorbed from the Sun at a mean surface temperature of around -18°C, 33° colder than the observed mean surface temperature of the Earth, which is 15°C. This process is referred to as the natural greenhouse effect.

The higher concentration of greenhouse gases (like carbon dioxide, methane, and nitrous oxide) in the atmosphere caused by human activities means that more radiation than normal remains trapped in our atmosphere. This creates an enhanced greenhouse effect.



Natural processes have changed the Earth's climate dramatically over the last 4.6 billion years. Over time, natural fluctuations in climate have caused the Earth to become, at various times, very cold and covered in ice, and very hot. In the past 10,000 years the planet’s climate has become increasingly stable, allowing for a flourishing flora and fauna, as well as a massive increase in human population.

However, over the past 50-100 years, warming at the Earth's surface has increased significantly and many of the observed changes since the 1950s are unprecedented over decades to millennia. Since the industrial revolution, the atmospheric concentrations of the main greenhouse gases - carbon dioxide, methane, and nitrous oxide - have increased to levels unprecedented in at least the last 800,000 years. Carbon dioxide concentrations have increased by 40% since pre-industrial times, primarily from fossil fuel emissions and secondarily from net land use change emissions. The ocean has absorbed about 30% of the emitted carbon dioxide from anthropogenic (human) activities, causing ocean acidification.

The latest Intergovernmental Panel on Climate Change (IPCC) AR5 Working Group I Report concludes that human influence on the climate system is clear and that it is extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century. Human influence has been detected in warming of the atmosphere and the ocean, in changes in the global water cycle, in reductions in snow and ice, in global mean sea level rise, and in changes in some climate extremes.

Source: IPCC AR5 Working Group I Report: The Physical Science Basis, 2013.

The IPCC WGI 2013 report states that continued emissions of greenhouse gases will cause further warming and changes in all components of the climate system. Limiting warming will require substantial and sustained reductions of greenhouse gas emissions.

The following graph shows projected changes in New Zealand's temperature compared to New Zealand's average temperature over the period 1986-2005. It shows that New Zealand has warmed by about 0.9 degrees celsius since 1990 and that New Zealand's temperature is expected to rise by another 0.8 degrees celsius or so above the 1986-2005 average if the world rapidly implements stringent measure to limit greenhouse gas emissions. By contrast, New Zealand's temperature is expected to keep on rising throughout this century - by about 3.5 degrees celsius above the 1986-2005 average - in a high carbon world.

Source: New Zealand Climate Change Centre, based on IPCC Working Group II Fifth Assessment Report Chapter 25.


Mitigation and adaptation - how do we minimise the impacts and adapt to a changing climate?

Mitigation: minimising change

The first imperative of climate change action is mitigation: the reduction of greenhouse gas emissions and the sequestration of carbon through planting trees and preserving forests. Mitigation activities aim to address the drivers of human-induced climate change so that the worst impacts can be avoided. Mitigation is critically important in the long term. But even the effects of aggressive mitigation are not likely to be evident within the next few decades, given that climate change effects resulting from past and current emissions are already “baked in” to the system.

The observed impacts of climate change are widespread and consequential. Climate change cannot be solved through mitigation alone; adaptation planning is also essential to reduce vulnerability to the increasingly severe and pervasive impacts of climate change already occurring.


Adaptation: preparing for change

Section 7 of the Resource Management Act requires that particular regard be given to matters related to climate change. In a local government context, wherever current climate is significant to an activity, hazard, or plan, the impact of a changing future climate should also be considered.

The RMA Quality Planning Resource on Climate Change (2013) states that Councils should explicitly consider whether the effects of climate change have significant implications for:

•Natural hazard management

•Land use planning

•The design and location of new infrastructure/assets with a lifetime of more than 30 years

The effects of climate change can also be integrated into councils’ longer term planning under the Local Government Act, as part of their mandate to meet the current and future needs of communities for good quality local infrastructure, local public services, and performance of regulatory functions in a way that is most cost effective for households and businesses.