The science behind climate change

Solar energy enters our atmosphere 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. This is 33° colder than the observed mean surface temperature of the Earth, which is 15°C. This process is the natural greenhouse effect.

The higher concentration of greenhouse gases in the atmosphere means that more radiation than normal remains trapped. 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. 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. The ocean has absorbed about 30% of the emitted carbon dioxide from 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.

The following graph shows projected changes in New Zealand's temperature compared to the average temperature over the period 1986-2005. It shows that New Zealand has warmed by about 0.9 degrees Celsius since 1990.  The 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.

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. This means reducing greenhouse gas emissions and sequestering 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. Even the effects of aggressive mitigation are not likely to be evident within the next few decades. 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 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, we need to consider the impact of a changing future climate.

The RMA Quality Planning Resource on Climate Change (2013) states that Councils should 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 part of councils’ longer term planning under the Local Government Act.

Updated June 7, 2022 at 11:20 AM

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