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What is Climate Change?

This page supports specialist and non-specialist teachers by providing background information about the concepts that underpin the LENScience resources on climate change and evolution.

Cycles of Climate Fluctuation


Google climate change and you will see an array of headlines, blogs and websites, all with differing information, issues and opinions.


Scientists understand that cycles of climate fluctuation are a natural and on‐going part of Earth’s climate systems. However, since the early 1970s scientists have been concerned at the effect of increased greenhouse gases in the atmosphere resulting from human activities. These increased greenhouse gases are raising temperatures and destabilising the Earth’s climate systems. They are changing the natural climate cycles.


Natural climate cycles are an important part of the Earth’s systems that cause changes in the physical (abiotic) environment and, through these changes, impact on the biotic environment within ecosystems. These environmental changes may alter selection pressures that could result in changes to the distribution patterns of species.  


Allan Wilson Centre Post Doctoral Fellow Ceridwen Fraser’s PhD saw her spend three years unravelling a story of the impact of climate cycles that is hidden in the DNA of Southern Bull Kelp (Durvillaea antarctica). Using modern biotechnologies to analyse DNA from Bull Kelp samples collected from the coastline of New Zealand, Southern Chile and Sub‐Antarctic Islands, Ceridwen discovered evidence that in the last ice age the sea ice was more extensive than previously thought, and that this has affected the distribution of populations of kelp that we see today.



Southern Bull Kelp is one of the world’s largest seaweeds, commonly found in the inter‐tidal zone around the southern coastlines of New Zealand, the sub‐Antarctic islands, Chile and the Falkland Islands. Anchored to the rocks by a strong holdfast, strands of this macro‐algae can stretch out more than 10m in length,  being tossed around by the strong waves and currents but held by this incredibly strong anchor. The holdfast creates a rich habitat for a large numbers of different invertebrates such as limpets, snails and crustaceans. Māori as well as people in Chile have traditionally made use of Bull Kelp both as a food and a material for making food bags and waka. Importantly, Durvillaea antarctica is buoyant. If pulled away from the rocks it will float, creating enormous rafts that carry their own invertebrate community with them. Not all species of Kelp are buoyant.


Understanding Climate Cycles

Climate cycles over geological time are thought to be caused by variations in the Earth’s orbital patterns (e.g. changes to the Earth’s axial tilt). These changes in climate can be traced by scientists through geological studies. Evidence shows that the Earth moves between glacial (frozen) and interglacial (warm) periods at relatively regular intervals lasting tens of thousands of years. Currently we are at the peak of an interglacial (warm) period. But the use of fossil fuels by humans is dramatically increasing the rate of global warming within this interglacial period.



Glacial Periods and Extinction Events 

As the Earth enters a glacial period, the decrease in temperature causes an increase in the area covered by ice. As well as ice expanding over previously habitable areas, sea levels fall as water is frozen into glaciers covering the land. Sea ice also expands across oceans, changing marine habitats; in the last glacial period the sea level was more than 120 metres lower than it is today. Figure 4 shows what New Zealand is thought to have looked like in the last glacial period, approximately 20,000 years ago. During a glacial period habitats can be altered, creating new selection pressures which can cause extinction events, particularly when a species is living near the edge of its habitat range.  


Interglacial Periods: Colonization and Possible Speciation 

Interglacial periods are the warm parts of the climate cycles. Ice melts and glaciers retreat, creating the potential for species to move back into habitats that were occupied by their ancestors thousands of years before. Species that have survived the glacial periods are often able to increase their range, colonizing new habitats, which can, over time, lead to speciation events. In addition, the melting glacial ice raises sea level, often creating islands out of previously connected land. These islands can provide isolated habitats (such as we know in NZ), which are known to encourage speciation events.