1 - Past Climates Flashcards
(41 cards)
1
Q
What is the difference between climate and weather
A
Weather is what happens on a day to day basis and is unpredictable, whereas climate is the average of the weather over a number of years. Typically over a 30 year period.
2
Q
What is a hothouse peridod
A
Warm periods in the earths history. Carbon dioxide levels 10-20 times larger than today. 2000ppm. Supports mega-flora and fauna. Around 3C warmer.
3
Q
What is an icehouse period.
A
Colder periods in the earths history. Carbon dioxide levels around half what they are today. 200ppm. Last one was the quaternary period which started 2.6m years ago and ended 11,000 years ago.
4
Q
What is paleoclimatology
A
the study of past climates
5
Q
What is a climate proxy
A
Preserved physical characteristics of the past which act as natural recorders of climate variability.
6
Q
What are examples of climate proxies.
A
- Ice cores
- Tree rings
- Sea floor sediments
- lake sediments (pollen grains, diatoms, varves)
- Fossils
6
Q
What are examples of climate proxies.
A
- Ice cores
- Tree rings
- Sea floor sediments
- lake sediments (pollen grains, diatoms, varves)
- Fossils
7
Q
Explain how ice cores can be used to reconstruct past climates.
A
- The ice contains tiny bubbles of air trapped during the initial ice formation.
- These bubbles of air provide a record of the gaseous composition of the atmosphere in the past.
- Measurements of greenhouse gasses can indicate temperature.
- They drill around a metre and a half of ice at a time until they reach the bottom.
- The further down they go, the further back in time.
- They can also look at oxygen isotopes (O18) found only in oceans that only find themselves in glaciers if the temperatures are high enough to evaporate them. More isotopes found in warmer conditions due to more energy to evaporate and transport them.
8
Q
How for back can ice cores measure past climates, and what are the issues of using them
A
- 800,000 years
- Can’t tell us millions of years ago
- Ice is melting fast so less places where older ice can be found
9
Q
How can tree rings be used to reconstruct past climates
A
- Each tree ring marks a year - darker band is winter growth, lighter band is summer growth.
- Thicker rings show warmer and wetter years, thinner rings show dryer and colder conditions.
- You can also see forest fires which could suggest warmer climates
- Works best in areas with a temperate climate and in wet conditions, or areas of drought.
10
Q
How far back can tree rings measure past climates and what are the issues with using it as a method
A
- 10,461 BC is the furthest back ever recorded, but many are around 2000 years old. Preserved wood is the oldest and can be up to 50,000 years old.
- Doesn’t go back very far and is more localised rather than showing a global or regional climate.
- There aren’t trees in a lot of areas.
- No indication of greenhouse gasses
- Is only an indication not accurate
11
Q
How can sea floor sediments be used to measure past climates
A
- Fossil shells of tiny creatures called foraminifera in sea-floor sediments and these can be used to reconstruct past climates
- These consist of shells of calcium carbonate and the chemical composition of these shells which can tell us the:
- Sea level
- Temperature
- Ocean conditions
- Amount of Magnesium in the shell exponentially increases from cold to warm water. This means that the Mg/Ca ratio of the shells is expected to rise with increasing temperature.
- They capture the ratio of O16 to O18 in the oceans which provide an insight into the global temperature. In hotter temperatures, the levels of O18 will decrease.
12
Q
How far back can sea floor sediments reconstruct past climates, and what are the issues of using them as a method
A
- Go back 100m years -> sampling intervals over centuries rather than specific years.
- Doesn’t give specific years only general time periods such as centuries.
13
Q
How can pollen grains in lake bed sediments be used to reconstruct past climates?
A
- Pollen analysis can show past vegetation types and in turn can be used to infer paleoclimatic conditions.
- Each pollen grain has a specific shape so can be matched to a species.
- The types of plants can suggest the past climate. E.g. Plants that prefer cooler conditions would suggest cooler conditions
14
Q
How can diatoms in lake bed sediments be used to reconstruct past climates
A
- Diatoms are microscopic plants found in lake sediments. They are mainly useful for past climates due to their high sensitivity to conditions.
- Past climates can be inferred from changes in species abundance for a number of indicator species. Core depth can be used to find a date
- Diatoms typically have high abundance in colder waters.
15
Q
How can varves in lake floor sediments be used to reconstruct past climates?
A
- These are tiny layers of lake sediment made up of light and dark bands.
- The light bands are formed of coarser sediments from spring and summer from high energy melt-runoff.
- Darker bands are made up of fine sediment and show deposition in the winter months
- Thicker varves are indicative of warmer varves and thinner varves are indicative of colder years
- Changes in varves can be plotted against time to determine variability.
16
Q
How can fossils be used to reconstruct past climates
A
- Plants and animals require specific enviromental conditions. Some are particularly sensitive to moisture and temperature fluctuations.
- Coral reefs are highly sensitive to temperature, water depth, and sunlight.
- These variations are revealed in annual growth rings similar to trees.
- The coral skeleton consists of calcium carbonate which is extracted from seawater - this contains oxygen isotopes - these can be used to determine the temperature of the water in which the coral use, and hence reconstruct the climate.
17
Q
What are the CO2, temperature, sea level and ice volume characteristics of hothouse vs icehouse periods.
A
Hot house:
- High CO2 concentration
- High temperatures
- High sea level
- Low ice volume
Ice house:
- The opposite to above
18
Q
Are we currently in an ice age?
A
Yes as there is permenant ice at the poles.
19
Q
In general, what has happened to the earths climate over the last 100m years
A
Transition from hot to colder global climate.
20
Q
What is the name of the interglacial period we are currently in
A
Holocene (however many would argue we are now in the anthropecene)
21
Q
What is the anthropecene
A
the time period in which human activities have significantly impacted the climate
22
Q
When did the antartica ice sheet start to form?
A
roughly 35 million years ago
23
Q
Is it more common for the earth to have ice caps or not?
A
More commonly hasn’t had ice caps over the last 500m years. Hothouse periods make up 70% of the last 2.5b years.
24
What was the global climate like 100m years ago
Significantly warmer.
25
When did the earth last switch from hothouse to ice house
34 million years ago
26
What period are we currently in?
Quaternary period. Started 2.6 million years ago.
27
What has happend to the climate druing the quaternary period?
Temperatures have dropped on average. The temperature has also been very cyclical - it goes up and down rapidly.
28
What was the main cause of Antartica's cooling 35m years ago.
- Antarctica's cooling was partially due to decreasing CO2 and therefore a drop in temperature but it was also aided by continental drift.
- It moved south to the current south pole and away from South America and Australia.
- This isolation lead to a cold current - the Antarctic Circumpolar Current forming and 'insulating' the continent from warmer waters further north.
29
How long do interglacials and glacials tend to last over the last 500,000 years
Glacials - 100,000 years
Interglacials - 10,000-15,000 years
30
What was the medieval warm period
- 900 to 1300 AD
- Around 1C to 2C warmer
- Very few direct measurements but warmer conditions seen through climate proxies.
- Prosporeous time in European history. Increased agricultural productivity / crop diversity - crops grown at higher latitudes and elevations than usual
- Definitely happened in Europe but debated if it was a global phenomenon
- Commonly cited by global warming sceptics as why there will be positives of climate change
31
What is the little ice age
- Around 1300 to 1800
- Northern hemisphere temperatures about 0.6C colder on average
- Very few direct measurements but cooler conditions seen through climate proxies.
- Likely caused by a series of large volcanic eruptions
- Cuased crop failures and famine in Europe and NA
32
What are milankovitch cycles?
These cyclical changes in the Earth’s circumnavigation of the sun create alterations in the seasonality of solar radiation reaching the earth’s surface and these times of increased or decreased solar radiation directly influence the earth’s climate system, impacting the advance and retreat of Earth’s glaciers.
- Precession
- Eccentricity
- Obliquity
33
What is eccentricity and how does it work?
| Milankovitch cycle no 1
- Period of 100,000 years
- Pull of gravity of Saturn and Jupiter causes earths orbit to vary from more circular to more eliptical
- When the earths orbit is more circular there is less difference between the insolation received at the closest and furthest distance from the sun each year. At maxiumum eccentricity this difference is 30%.
- Glacial periods at maximum eccentricity
- Currently almost at most circular orbit
34
What is obliquity and how does it work?
| Milankovitch cycle no 2
- The angle of the earths tilt changes over a period of 41,000 years from 22 to 24.5 degrees.
- The tilt of the earth is the reason we have seasons.
- When the tilt is closer to 22 degrees seasonal differences are reduced, therefore the difference in insolation received by the poles and equitorial areas.
- This means snow and ice accumulating in the winter at the poles does not melt in the summer causing the growth ice sheets.
- The northern hemisphere (which has more land) doesn't get as hot in the summer, causing ice to build up.
35
What is precession and how does it work
- As the earth rotates it wobbles slightly due to gravity from the sun and moon over a period of 22,000 years
- This means that the point in the earths orbit that it is closest to the sun (perihelion) varies
- Changes in precession impacts the intensity of the seasons
- If perihelion occurs during the northern hemisphere winters, winters will be warmer and summers cooler. Therefore snow and ice wont melt as much during the summer.
- Currently N hemisphere is when winter is closest to the sun
36
How do volcanic eruptions impact the earths climate
- Huge amounts of volcanic ash and sulphur dioxide are pumped into the stratosphere
- Sulphur dioxide is converted to sulphuric acid which forms sulphate aeorsoles which relect insolation back into space and thus have a cooling effect
- EG: Mount Pinatubo 15th june 1991 injected 20million tonnes of sulphur dioxide into the atmosphere and cooled the earths temperature by 1.3C over a 3 year period.
37
How do plate tectonics and continental drift impact the climate
- Impacts balances of incoming and outgoing radiation
- Where larger continents occupy higher latitudes, there is an increased albedo and global cooling
- 250m years ago the continents formed a single super continent known as Pangea
- Also alter ocean currents, which impacts the distribution of heat across the earth causing different areas to become warmer or colder
- EG: When NA and SA joined 5m years ago the Gulf Stream was intensified which increased precipitation and diluted the NA which inturn reduced the heat transfered in the N Atlantic and caused the advance of ice sheets, increasing albedo.
38
How do sunpots influence the climate
- Follows and 11 year cycle and sunspots cause an increase in solar output and causes slight warming. This is not enough to impact the climate significantly
- Over longer time periods it can be more variable, as near the end of the 17th century the number of sunspots dropped to almost 0 for several decades causing severe winters in what is known as the 'little ice age'.
- Sunspot activity has been high in the last 50 years
39
How does ocean salinity influence the North Atlantic Drift
Melting of ice sheets in the arctic reduces ocean salinity, making the ocean less dense and reducing downwelling. This slows the whole North Atlantic drift, and as a result Europe recieves far less heat from the oceans. This led to glacial conditions around 12,000 years for 1000 years in northern europe despite the general trend of warming global conditions. This was known as the Loch Lomond stadial.
40
How do natural greenhouse gasses influence the climate?
- Close relationship between CO2 and temperatures
- During the last 800,000 years CO2 levels have varied between 170 and 300ppm during glacials and interglacials respectively. (Currently at 420ppm showing the rapid increase)
- Formation of fold mountains increases carbonation weathering which locks up carbon in the lithosphere over millions of years.
- Phytoplankton increases locks up carbon in sedimentary rocks.
