Climate Change

Climate is continuously changing, and through studies of ice cores and the rock record we can see that throughout the Earth's history the climate has changed a number of times. Climate change has been linked to most of the main extinctions (late Cambrian, late Ordovician, end Permian, the K-T event and the late Triassic.) Climate change often happens as a result of other factors such as volcanism and impact and can lead to the loss of many species.

Getting HOTTER

During the Permian the continents were in one landmass called Pangea. As all the land was together and was so large, there was a hot dry interior because a majority of the land was away from the sea and experienced little rainfall. It also had great seasonal fluctuations due to the lack of the moderating affects of a large water body. The climate's temperature may have risen due to the increase in volcanic activity. During the end of the Permian the Siberian traps were erupting, releasing vast amounts of different gasses into the atmosphere.

One of these gasses was Carbon dioxide (CO2). This has an insulating affect on the atmosphere making the climate temperature warmer. Increased climate temperature has also been shown to slow the metabolism of creatures, and upset the formation of internal and external carbonate (CaCO3) skeletons. Many marine organisms have carbonate skeletons. If these creatures were unable to form their skeletons they would have either no support for their bodies or no external protection, so would be unable to survive. (A. H. Knoll) A hotter climate of the low latitudes during the Permian lead to a reduction in the area of coal swamps. As this habitat decreased, species that lived there, such as amphibians and some spore bearing plants, became extinct.

Getting COLDER

As well as getting hotter there is evidence that the climate also cooled. Sedimentological evidence for cooling comes from glacial deposits in polar zones, and thick dune sands and evaporites from temperate zones that represent a cool dry environment. As already discussed in the section on Vulcanism some of the volcanic gasses released from the Siberian trap flood basalts could have the opposite affect to the CO2, cooling the climate instead of heating it. Other evidence comes form the reduced presence of carbonate limestones around the end of the Permian. This process would have had the greatest affect in the tropics where most of the Earth's limestone production occurs. Cooling would eliminate the tropical ares and kill tropical species, and if there were less Carbonate producers there would be less carbonate which is what is seen.

Another cooling affect comes from glaciation. Cooling can happen in low latitudes without there being glaciation and in this way just the cooling of the climate would be the cause of extinction by the method mentioned above.

What did these temperature changes do?

The cooling methods appear to contradict the evidence for heating. However, if chilling and heating happened repeatedly, with geologically rapid repeated heating and cooling occurring, many species would not have time to adapt to the alternative environment. Many that were not able to live in the new climate would have suffered depletion in numbers and possibly extinction.

A cooler climate on its own would have left warm tropical taxa with nowhere to go that with the correct temperature for them, so they would had to have adapted or die out.

A cooler climate has also been linked to changes in ocean circulation. When there is a cool climate, there are changes in the sea's circulation patterns. Water from the deep oceans which is laden with CO₂ and hydrogen sulphide (H₂S) is bought up to the surface. There is also the possibility that methane (CH₄) could also escape from sea floor sediments when they are disturbed by circulation changes. Not much of these compounds are normally found in surface waters and the presence of them in abnormally large quantities could kill many marine organisms.

The changing climate could also have affected terrestrial species in that it would alter vegetation patterns which would lead to food shortages for smaller animals,which in turn caused food shortages further up the food chain. The cold glaciated seas and the toxic compounds bought up to the shallow seas could suggest why so many more marine species became extinct compared to terrestrial extinctions.

It also has been postulated that changes in salinity can occur due to a hotter climate because of the increase in halite deposits. More halite on land would mean less salt circulating in the oceans. Fluctuations in salinity would alter the marine environment which would lead to the selective extinction or reduction in numbers of families that were not able to cope with such changes.