About climate change
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tterns will intensify
gases are changing the earth’s temperature
simply ‘global warming’There is uncertainty in all climate change models
There is now clear international evidence that the world’s climate is changing. Between 1880 and 2012, the world warmed by an average of 0.85°C. Other evidence includes a rise in sea levels, melting of Northern Hemisphere snow and ice, and a change in ocean temperatures .
We define ‘climate change’ as:
- a change in the state of the climate
- which could be a change in the ‘average weather’, or how varied the weather patterns are
- that continues for decades (or longer) .
In New Zealand the Resource Management Act 1991 defines climate change to mean:
a change of climate that is attributed directly or indirectly to human activity that alters the composition of the global atmosphere and that is in addition to natural climate variability observed over comparable time periods.
NZ climate scientists predict that New Zealand’s weather will change in the following ways [3,4]:
- Warming: All of New Zealand is very likely to warm about 1°C by 2040 and 2°C by 2090. There will be more very hot days, and fewer very cold days.
- Rainfall: The West Coast region will have more rain. North and eastern parts of the North Island and the east of the South Island will have less rainfall.
- Droughts: Droughts are likely to occur more often, especially in the east of both islands, and the Bay of Plenty and Northland.
- Fire danger: There are likely to be more days with very high and extreme fire danger in eastern New Zealand, the Bay of Plenty, Wellington and Nelson.
- Wind: The South Island is likely to get windier on average, particularly in winter.
Climate scientists state that the changes in climate are primarily due to anthropogenic (human-produced) activities, rather than part of the earth’s natural variation . Human activity causes an ‘enhanced greenhouse gas effect’.
In a greenhouse, the glass lets the sun in to warm the room, but it also prevents the warm air escaping. The room stays warm. The earth’s atmosphere acts in a similar way, trapping the heat from the earth’s warm surface to maintain a comfortable temperature for the earth (Figure 1).
Figure 1: The Greenhouse Effect
Greenhouse gases are carbon dioxide, nitrous oxide, methane, ozone, water vapour, and chlorofluorocarbons. Since industrialisation, these gases have been produced in much greater amounts by human activities – particularly burning fossil fuels.
The increase in greenhouse gases means that more of the sun’s energy is trapped near the earth, rather than passing into the outer atmosphere. This has changed the earth’s temperature balance mechanism .
Climate scientists predict that the world will warm by 0.3–4.8°C before the end of the 21st century . This projection is an average across the whole world. It is also a long-term trend. On a year-to-year basis, we are not likely to notice a warming climate.
Some places are predicted to warm more than others, and much of the warming will be absorbed by the world’s oceans. This warming expands the oceans, leading to sea level rise. The warming temperatures are melting sea ice and glaciers, and the extra water that flows into the world’s oceans will also raise sea levels.
In addition to average warming, many areas of the world are predicted to have more extreme weather events like intense rainfall, storms and floods.
At the same time, there are also many areas of the world that are likely to see periods of drought. It is possible to have more drought and more floods if there are short periods of intense rainfall but a lack of rainfall at other times.
Models of climate change use known facts as well as assumptions to predict how things will be in the future. Climate models often give a range of estimates to show how things will be if one or more factors change. This means there will always be some uncertainty.
Climate models done by different people have similar predictions, and we can use the models with past climate data to accurately ‘predict’ the current climate. This gives the models more ‘weight’.
1. IPCC. 2013. Summary for Policymakers. In TF Stocker, D Qin, G-K Plattner, MMB Tignor, SK Allen, J Boschung, A Nauels, Y Xia, V Bex and PM Midgley (Eds.), Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge, United Kingdom and New York, NY, USA: Cambridge University Press.
2. IPCC. 2006. Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge, United Kingdom and New York, NY, USA: Cambridge University Press.
3. Ministry for the Environment. 2008. Climate Change Effects and Impacts Assessment: A guidance manual for local government in New Zealand. Second edition. Wellington: New Zealand Climate Change Office, Ministry for the Environment.
4. Reisinger A, Kitching R, Chiew F, Hughes L, Newton P, Schuster S, et al. 2014. Australasia. In V Barros, C Field, D Dokken, M Mastrandrea, K Mach, T Bilir, M Chatterjee, K Ebi, Y Estrada, R Genova, B Girma, E Kissel, A Levy, S MacCracken, P Mastrandrea and L White (Eds.), Climate Change 2014: Impacts, Adaptation, and Vulnerability. Part B: Regional Aspects Contribution of Working Group II to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge, United Kingdom and New York, NY, USA: Cambridge University Press.
5. IPCC. 2007. Climate Change 2007: Synthesis Report. Contribution of Working Groups I, II and III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Core Writing Team, Pachauri, R.K and Reisinger, A (eds.)]. Geneva: IPCC.