Global climate - natural greenhouse effect + natural variations in solar radiation Flashcards
What does the natural greenhouse effect do?
- Regulates Earth’s climate
- Keeps Earth’s surface at 15 degrees C average (ideal for life)
- which would otherwise be 33 degrees C lower (-18 degrees C = impossible for life)
How long has the natural greenhouse effect been taking place? and what causes it?
Caused by greenhouse gases
- A natural process that has always been present + predates human activity on Earth
What are greenhouse gases and examples of them?
They occur naturally in Earth’s atmosphere
Include:
- Methane
- Carbon dioxide
- Water vapour
- Nitrous oxide
How do greenhouse gases work?
Allow solar radiation to pass through/into the atmosphere - but then trap the heat like a ‘blanket’
- UV shortwave radiation passes through, but they absorb (trap) long-wave infrared radiation
- this infrared radiation is then re-radiated/ re-emitted by the Earth (heat energy).
What are the stages of the natural greenhouse effect?
- Short-wave radiation passes through atmosphere
- Some short-wave radiation is absorbed and is converted into long-wave radiation
- Some long-wave radiation passes back into space
- Some long-wave radiation is reflected off greenhouse gases back to Earth, heating Earth up
What kind of energy system does our atmosphere have?
The atmosphere is an open energy system, receiving energy from the sun
- Energy can enter and leave the atmosphere
- Inputs: insolation (solar radiation)
- Outputs: re-radiation
How much energy is lost to space through reflection?
31% (other 69% is lost later on)
How much energy is absorbed at the surface (which is then later lost to space)?
46%
Why is the Earth’s solar budget due natural conditions?
It’s a balanced system
- Radiation Input = Radiation output
(the Earth is neither heating nor cooling)
Where on Earth is the most solar energy received?
Most solar energy is received at the equator
Where is the least solar energy absorbed?
At the equators
What are the reasons for the Earth’s energy balance (places on Earth where more energy is absorbed than other areas)?
- Effect of latitude on insolation
- Seasons affecting amount of insolation
- Effect of cloud cover on insolation
What is the effect of latitude on insolation?
- Sun’s energy = more concentrated at equator than poles, where it spreads over larger area (less heat per km^2 at poles)
- Sun’s energy travels through more atmosphere at poles + more energy absorbed by dust and pollen particles before it reaches surface
- Angle of the sun is lower in the sky at the poles + more energy reflected into space
- Snow + ice at poles also reflects more insolation than the land and sea at the equator
How do warm and cold currents redistribute energy around Earth?
- Warm water moves from equator to poles
- Cold water moves from the poles towards the equator
Why does the UK experience milder winters than expected?
For its latitude, winters should be colder, but due to the warming influence of the North Atlantic Drift, the winters are much milder than expected
How do seasons also affect the amount of solar radiation (insolation) reaching different parts of the Earth?
Spring Equinox - 21 March
Winter Solstice - 21 December
Autumn Equinox - 23 September
Summer Solstice - 21 June
- This is because of the tilt of the Earth’s axis in relation to the sun
How is the effect of insolation reaching Earth affected by seasons exampled in the month of December?
- Northern hemisphere is tilted away from the sun
- Further north from the equator, days are shorter, less insolation received (e.g. UK)
- Southern hemisphere is tilted towards the sun
- Further south from the equator, days are longer, more insolation receiver (e.g. Australia)
What is the effect of cloud cover on insolation in Earth?
Stratocumulous clouds
- Less cloud cover = more insolation reaches
Earth’s surface
How long are the natural changes in the amount of solar radiation reaching the Earth?
Occur over different timescales (temporal patterns):
- Short-term (rapid - over years / decades)
or
- Long-term (slow - over centuries / millenia)
What is the main example of long-term, natural variation in solar radiation + climate / temperature?
The glacial - interglacial cycle
For how long have there been a series of Glacials + Interglacials?
Over the last 2 million years
What are Glacial periods?
Relatively cool periods
100,000 years
What are Inter-glacial periods?
Relatively warm periods
10,000 - 10,000 years
What is our present Inter-glacial period called, and how long has it lasted?
The Holocene started around 12,000 years ago
What provides us with evidence of these glacial/inter-glacial periods and how long they’ve lasted?
The Vostok Ice Core, Antarctica
- Evidence can be seen in the CO2 levels in the Vostok Ice Core
- provides over 400,000 years of climate data
What is the difference in the amount of ice present in glacial vs inter-glacial periods?
Earth in the Devensian Glacial:
- Cooler = more ice
Earth in the Holocene inter-glacial (now):
- Warmer = less ice
Why does Earth experience glacial and inter-glacial periods?
Because Earth’s orbit around the sun varies:
- from circular to elliptical
Why does Earth’s orbit vary from elliptical to circular?
Because of the gravitational pull from other planets
What are Milankovich cycles?
The changes in the Earth’s orbit affecting the amount of solar radiation heating Earth’s surface, and therefore Earth’s temperature:
- Elliptical = cooler = glacial
- Circular = warmer = inter-glacial
How long do Milankovich cycles last?
The cycle from elliptical orbit to circular completes every 100,000 years
What is stage one of the Milankovich cycle?
A change - elliptical orbit - in the Earth’s orbit kick starts the process of long-term climate change
- Less insolation
- Climate 0.5 degrees C cooler
What is stage two of the Milankovich cycle?
The Albedo effect takes over, exaggerating the effect, causing temperatures to fall further and a glacial to occur
- more white snow + ice
- Earth’s albedo (reflectivity) increases
- More insolation reflected into space
- Climate 5 degrees C cooler ( = glacial)
How is the process then reversed after the first two stages?
Reversed by a return to circular orbit
- more insolation
- climate 0.5 degrees C warmer
- less white snow + ice
- Earth’s albedo decreases
- less insolation reflected into space
- climate 5 degrees C warmer ( = inter-glacial)
How does the albedo effect affect the Milankovich cycle?
It amplifies the Milankovich cycle / glacial - inter-glacial cycle
When does the surface of the Earth absorb more heat?
When a surface doesn’t have snow or ice it absorbs more heat
What does a low albedo cause?
- 30% of insolation is reflected with low albedo
- low albedo = inter-glacial
What does a high albedo mean?
- 90% of insolation is reflected with high albedo
- high albedo = glacial
What evidence is there for the glacial cycle in Britain?
- When ice melted in Yorkshire about 2,000 years ago -> cargo of rocks was dumped miles away from home
- These rocks were picked up by the glaciers + moved until the glacier melted
- these out-of-place rocks are called erratics
- Glaciers shaped everything in their path - gouged out some of the most spectacular landscapes in Britain
What evidence is there for the inter-glacial cycle in Britain?
- Most of last 2 million years - Ice Age was cold, but..
- In London in 1930, builders dug up a collection
exotic bones- e.g. one bone is 120,000 years old (which
would place it in the middle of an ice age - however it does not belong to a wooly
mammoth or polar bear - Instead it’s the tooth of a hippopotamus
- e.g. one bone is 120,000 years old (which
- This proves that the Ice Age was punctuated by
warmer periods (some even warmer than today)- proves that right in the middle of London,
120,000 years ago, icy wilderness was replaced
by Serengeti plains
- proves that right in the middle of London,
- In London in 1930, builders dug up a collection
- Glaciers –> Swamps
- Mammoths –> Hippos
What are examples of natural short-term changes in the climate?
- Sun spots
- Global dimming / Volcanic cooling
What are sunspots?
Sunspots are the result of Magnetic storms which release increased solar radiation to Earth
How often do sunspots occur?
An 11 year cycle has been identified
How do sun spots create short-term changes in Earth’s climate?
As the number of sunspots increases, so does the temperature on Earth
- are evidence of high energy phases in solar activity
What provides evidence for the effect sunspots had on Earth’s climate (UK example)?
1694 ‘frost fair’ on the Thames in London
- The Thames often froze in winter and ‘frost fairs’ were held on the ice
- During a period of colder temperatures known as the Little Ice Age, when winter temperatures were 2 degrees C lower than normal
What was the coldest period of the Little Ice Age called?
The Maunder Minimum
- a period of few sunspots = low solar energy
How long do Northern Hemisphere changes last?
10,000 years (average temperatures varied, but these are relatively small + short in terms of geological time)
