1.A Flashcards
Method used to reconstruct earth’s climate - Marine sediment and fossils
Coral reefs live in tropical waters. They need a particular temperature, specific depth of water and right amount of light. If depth of water changes just a fraction – cannot survive. Different species of plantsand animals need different conditions to survive. – som ecan be very sensitive to climate and not adapt easily to this change. – Thereofre when fossil corals are found its possible to estimate precisely the environemtn they lived in by assuming that they need the same conditions as those that thrive today. The chemical compsotion of shells help indicate the ocean temp in which they formed in.
Method used to reconstruct earth’s climate - ice cores
Relies on the analysis of ice – you analyse the isotopes in each layer. It is possible to measure how cold or warm the climate was at the time the snow fell. Ice sheets form when layers and layers of snow build up and gradually turns to ice . Once ice core removed – demonstrates layers showns that you are able to to count back as one layer = a year. Possible with modern tech to extract gas bubbles from within the ice – recorded earths at at the time. Ice cores show us that whe gas concentrations have gone up, then the temp had also gone up in parralell
Method used to reconstruct earth’s climate - dentrochronology
Study of tree rings is the dating of past events such as climate change through tree ring growth . Vary in width each year depending on tenp conditions and moisture availability. Tree rings are the cambium layer – lies between the wood and bark. – how large these cambium cells grow each year. Environmental inputs into cambium are primarily regional climatic variations, changes in temp, aridity and soil chemistry. – during dry seasons cambium cells are smallers and layer is thinner in wet seasons.
Method used to reconstruct earth’s climate - lake sediment
reconstructed from pollen grains, spores, diatoms and carves in lake sediment.
Pollen analysis identifies past vegetation types and fro this - infers palaeoclimatic conditions. Pollen diagrams show number of identifies pollen types in different sediment layers.
Diatoms = single creed algae found in lakes with cell walls made of cilia. they record evidence in their shells.
Varves are tiny layers of lake sediment comprising alternative light and dark bands - light = formed from coarser sediment indicate high energy, meltwater, spring and summer. Darker = made up of fine sediment shows deposition during winter months.
Past climate - glaciation of Anatatica
- continent is covered with ice caps so thick only tops of highest mountains appear - above ice
- 40 million years ago the continent = experienced sub tropical conditions
- 35 million years ago - when the icehouse state occurred
Transition to this icehouse conditions = explained by changes in atmospheric co2 and tectonic processes
Past climate - glaciation of Anatatica - co2 levels
- co2 levels dropped 35 million years ago abruptly from 1000 ppm to 600 ppm
Past climate - glaciation of Anatatica - continental drift
movement of Antartica towards the South Pole and away from SA and Aus isolated the continent.
Past climate - glaciation of Anatatica - growth of south sandwich islands submerged volcanic arc
= disrupted deep water ocean currents around Antartica - isolating continent from warmer waters.
Past climate - Quaternary glaciation
- spans the last 2.6 million years - main feature is the cyclic change of climate with long cold periods or glacials interrupted by short and warmer inter glacials.
- during glacial periods av annual temps in NW EU remained below zero.
- in the past 450,000 years - 4 major glacial episodes
Past climate - The Holocene
- current geological period
- begun at end of last glacials 111,700 years ago - an inter glacial period
- ice sheets and glaciers have shrunk and sea levels has risen by over 100m and with exception of antatrtica and Greenland ice sheets have disapepread from continental surfaces.
- Almost global climate - warmed steadily - not been continuous and serveral short episodes of warmer/cooler
- vast majority of scientists believe c.c in last 200 years - driven by human acitivity -enetring a new geological period called Anthropecene.
How has natural forcing driven climate change? - Plate tectonics continental drift: LT
The positions of continents change over time due to continental drift due to plate tectonics. This can then further influence the amount of land in higher latitudes and therefore the amount of ice cover. The impacts of this are that as continents gradually drift to higher latitudes, this causes lower temps therefore more snow accumulates causing ice sheets to form and increase the surface albedo with more isolation reflected creating a cooling effect.
- occur on a regional and global scale - large impact on the global ice cover.
- These currents absorb heat from the atmosphere and increase the sea surface temperature where this circulation transports warm and cold water all around the globe leading this to have a global impact. Even such a small change to these currents will cause a large effect on climate as these currents absorb such a large amount of heat. 5 million years ago, the land masses of North America and South America started to join at the Isthmus of Panama. This event in turn established the Gulf Stream warming North West Europe and even leading to the triggering of the Quaternary Ice Age.
How has natural forcing driven climate change? - Milankovitch Cycles: LT - ECCENTRICITY
Eccentricity is a cycle of every 100,000 years where a stretched orbit caused to retreat and advance.
- Different in solar radiation receipt of 30% between perihelion and aphelion and the Ice Ages correspond to periods of maximum orbital eccentricity.
- The more elliptical it is, the colder the climate will be.
How has natural forcing driven climate change? - Milankovitch Cycles: LT - OBLIQUITY
Every 41,000 years obliquity occurs. The smaller the tilt, less seasonal variations therefore colder climates, for example cooler summers. Therefore, snow accumulates forming more glaciers increasing a positive feedback effect. This then causes more reflection of incoming solar radiation which decreases the temperature.
How has natural forcing driven climate change? - Milankovitch Cycles: LT - PRECESSION
every 22,000 years precession occurs. This affects the point in the year when the earth is closest to the sun and when earth is furthest away during the Northern summer, causes a cooler summer therefore resulting in a similar situation and obliquity where a positive feedback loop occurs.
How has natural forcing driven climate change? - Solar Output (sunspots) - ST
Is varies over time and isn’t a constant occurrence. UV radiation increases dramatically during high sunspot activity casing more energy to be delivered resulting in global temperatures to increase. Therefore, showing that scale is related to the level of impact as the temperature increase depends on the scale of sunspot energy and UV radiation being emitted. Although this is seen to have a large impact, most scientists believe there is only a 0.1 % variation which is very subtle compared to other factors therefore there is not a long enough influence to have a significant impact.
