Key facts about climate change
The Earth is getting warmer
There is lots of evidence that tells us the average temperature of the world's atmosphere and oceans has increased - not just direct temperature measurements on land and at sea, but also changes in the dates when lakes and rivers freeze and their ice melts, the extent of snow cover, reduction in glaciers, extension of the growing season, and changes in the heat stored in the ocean. A number of biological changes have also been observed including poleward and upward shifts in the range of some plant and animal species, and earlier timing for some species of spring events such as leaf-unfolding, bird migration and egg-laying. These indicators provide unequivocal evidence that the climate is changing.
Human activities are very likely the cause of long-term climate change
Humans have added significant amounts of greenhouse gases to the atmosphere since the industrial era, primarily through the burning of fossil fuels and clearing of forests. Adding more of a greenhouse gas like carbon dioxide to the atmosphere intensifies the greenhouse effect, by trapping heat within the Earth’s troposphere, in turn warming the Earth’s climate. Long-term climate change is being driven primarily by the levels of these gases in the atmosphere.
Levels of carbon dioxide and methane are increasing
The levels of carbon dioxide and methane in the atmosphere have increased as the result of human activities and are now higher than they have been in 650,000 years.
We know this from a number of ice core studies. Snow traps tiny bubbles of air as it falls and is compressed into ice. Over the years, more and more ice layers stack up on top of each other. Drilling into ice sheets in Antarctica and Greenland provides a record of what the atmosphere was like back in time.
These analyses provide very clear and consistent results that today's greenhouse gas concentrations are now far higher than they were at any time during the past 650,000 years. Other measurements, such as atmospheric concentrations, show how our global greenhouse gas emissions have grown. Global emissions have grown by 70 per cent between 1970 and 2004.
If we don’t reduce global greenhouse gas emissions, carbon dioxide levels will continue to rise during the 21st century
The Intergovernmental Panel on Climate Change (IPCC) has used a range of scenarios to determine what might happen to the world’s atmosphere if we don’t take action to reduce global greenhouse gas emissions.
The scenarios indicate it is very unlikely that carbon dioxide concentrations in the atmosphere will stabilise before 2100, unless global action is taken to reduce emissions.
Without action, the rate of global temperature change over the next 100 years will almost certainly be unlike anything human civilisation has experienced before
Climate changes have occurred naturally in the past, and some regional changes have been significant. But globally, our climate has been relatively stable for the past 10,000 years. If the world does not take action to reduce greenhouse gas emissions, the global average temperature is very likely to change more rapidly during the 21st century than during any natural variations over the past 10,000 years.
Climate change is not just rising temperatures
Under climate change New Zealand can also expect to see changes in wind patterns, storm tracks, the occurrence of droughts and frosts, and the frequency of heavy rainfall events. The impacts of climate change in New Zealand will become more pronounced as time goes on.
The effects of climate change will continue beyond 2100. Sea-levels will continue to rise for centuries after greenhouse gas concentrations have stabilised
The climate system takes time to change. In particular, the deep oceans take centuries to heat up when the atmosphere above them warms. This means that oceans will continue to heat up, and therefore expand causing sea-levels to rise, even if greenhouse gas concentrations in the atmosphere are no longer increasing.
The climate system is very complex and there are still uncertainties about future climate changes.
Future climate change depends on how much greenhouse gases are emitted in future (and hence on the development pathway of human society) and also how the Earth responds to the increased heating. So we cannot be precise about how much the climate will change in the future. We are generally sure of the direction of change (for example, the world will become warmer, and global average sea-levels will rise), and we can give plausible ranges for those changes (for example, the range of emissions looked at by the IPCC is expected to increase the world’s average temperature by between 1.1 and 6.4 degrees Celsius by 2100).
Want to learn more?
The Ministry for the Environment website provides more information on domestic and international action against climate change:
For more information on the science of climate change:
- Impacts of climate change in New Zealand
- Advice from the Prime Minister’s Chief Scientific Adviser
- The Intergovernmental Panel on Climate Change’s comprehensive assessments of climate change. This includes the reports on The Physical Science Basis, Impacts, Adaptation and Vulnerability and Mitigation of Climate Change from the IPCC 4th Assessment 2007.
Last updated: 1 November 2010
