1a- how has the climate changed in the geological past Flashcards
how are marine sediments used to reconstruct the past
The chemical composition of fossil shells of foraminifera can be used to indicate the ocean temperature in which they formed. They can show how the climate is variable in one location.
how are ice cores used to reconstruct the past
ice is formed at the poles when there is a high proportion of the O-16 isotope compared to O-18 so the ice traps the air and the precipitation that forms the ice and when we take an ice core we can see back 800,000 years
how are fossils used to reconstruct the past climate
plants and animals require specific conditions to thrive e.g coral reefs are very sensitive to temperature. Their fossils can be used to figure out what the climate was like at the time they were alive
how dendrochronology is used to reconstruct the past
tree rings can be used as the rings (annules) vary in size depending on temperature conditions and moisture availability that year.
how are lake sediments used to reconstruct the past
Pollen analysis identifies past vegetation types and from this, the climatic conditions can be inferred.
Diatoms which are found in lakes record evidence of past climates in their shells
Varves are tiny layers of lake sediment with light and dark layers, the light bands are coarser sediment and indicate high energy due to meltwater in the spring/summer and the darker bands are finer sediment which shows deposition in winter months.
how has plate tectonic driven climate change (natural forcing)
Pangea splitting meant land moved to higher altitudes and so there was more ice and more albedo which led to cooling (pfl)
when the isthmus of Panama was formed the gulf stream intensified 5 million years ago and so NW Europe warmed which led to increased evaporation and precipitation which led to decreased salinity which reduced downwelling in the north Atlantic so the Gulf stream and thermo-haline circulation were affected.
The decreased salinity and heat being transferred by the gulf stream triggered the Quaternary ice age.
Towards the end of the last ice age when the ice was melting the salinity decreased and the gulf stream weakened again so glacial conditions continued in Europe this was the younger dryas period
how has solar output driven climate change (natural forcing)
the energy emitted by the sun is intercepted by the earth, we measure it by observing sunspots. There is a positive correlation between the number of sunspots and solar energy output.
On a long-term scale solar output is variable e.g in the 17th century there were very few sunspots and this corresponded to the ‘Little ice age’ but it’s hard to isolate the impacts of variations in solar output from other influences.
how has volcanic activity driven climate change (natural forcing)
ash and sulphur dioxide pumped into the atmosphere has a cooling effect, sulphur aerosols are formed and they reflect solar radiation back into space and decrease the temperature
how have Milankovitch cycles driven climate change (natural forcing)
obliquity- the earth’s tilt varies from 22-24.5 and when its smaller the seasonal differences in temperature are reduced this means snow and ice accumulated during winter won’t melt in the summer so glacial expansion will occur albedo means pfl.
Eccentricity- how elliptical the earth’s orbit is which is affected by the pull from Saturn and Jupiter. The biggest eccentricity causes uneven seasons as it affects distance from the sun
Precession- the perihelion changes over time due to gravitational influence of moon and Jupiter wihc effects the intensity of the seasons, if perihelion occurs in winter then winters will be warmer and summers cooler snow and ice wont melt in summer so snow and ice expands
how has natural greenhouse effect driven climate change (natural forcing)
there is a close relationship between atmospheric CO2 levels and average global temperatures, low co2= low temperature. we can use ice cores to see what the levels of co2 were in the past and use this to predict the temperature. When the temperature decreased CO2 dissolves and the temperature decreases further.
how has the climate changed over time (long term change)
100 million years ago the global temperature was 6-8 degrees higher than today so tropical conditions extended to Antarctica and Alaska this coincided with higher co2 levels.
35 million years ago there was a rapid transition to colder conditions due to reduced co2.
how has the climate changed over time (glaciation of Antarctica)
35 million years ago Antarctica went rapidly into an icehouse period due to;
co2 levels dropping abruptly by about half
continental drift towards the south pole so the Atlantic Circumpolar Current insulated Antarctica from warmer water
the south sandwich islands disrupted the deep water ocean currents around Antarctica and isolated it from warmer water
how has the climate changed over time (quaternary period)
the quaternary glaciation has been cyclical changes of climate with long glacial periods dispersed with short interglacial periods
20,000 years ago the Devensian reached its maximum and 1/3 of the surface was covered by ice and snow
The last time Britain had glaciers was the younger dryas period 13,000 years ago
how has the climate changed over time (the holocene)
the Holocene is the current interglacial period. Ice sheets have shrunk so the sea level has risen by over 100 meters and remnants of the valley glaciers only survive in high mountains like the Himalayas.
there have been short-lived periods of cooling like the Medieval warm was followed by the ‘little ice age’ when temperatures fell and Europe was sent into deep freeze.
Last 200 years of climate change has been driven by humans and our influence on global climate has become dominant- new period called the Anthropocene
