unit 2.1
what is the milankovitch cycle?
a cyclical movement related to the Earth's orbit around the Sun. there are three of them: eccentricity, axial tilt, and precession
define the greenhouse effect
a natural process and one that is vital to the existence of humans. without the greenhouse effect the earth will be significantly colder and unable to support large scale life
what is the maunder minimum?
a period when europe experienced harsher winters because of low sunspot activity. it was dubbed as the little ice age
4 other main components of the atmosphere?
argon, neon, helium, krypton
define negative feedback
changes in a system that tend to dampen or buffer changes; this tends to hold a system to some equilibrium state making it more stable. (decreases)
define positive feedback
enhance or amplify changes; this tends to move a system away from its equilibrium state and make it more unstable. (increases)
define long wave radiation
is the energy leaving the earth as infrared radiation at low energy and contains less energy than shortwave radiation. (generally emitted by cold bodies)
what is blocking?
occurs when the jet stream forms an s shape over the north eastern atlantic causing the wind to fall back over itself and affects the dynamic of jet streams
define energy balance
the balance between incoming short wave radiation and outgoing short wave and long wave radiation
define short wave radiation
the energy from the sun that enters the earth's atmosphere (very short wavelengths) such as ultraviolet and visible light. (generally emitted by hot bodies)
define albedo
the fraction of Sun's radiation reflected from a surface. OR the ratio between the total solar radiation reaching a surface and the amount reflected
define enhanced greenhouse effect
the impact on the climate from the additional heat retained due to the increased amounts of carbon dioxide and other greenhouse gases that humans have released into the earth's atmosphere since the industrial revolution
define conduction
the transfer of heat by contact
define convection
the transfer of heat by movement of a gas or liquid
blocking: with and without ?
with: cold dry winters without: mild, wet winds (uk weather)
example of negative feedback
- a good supply of grass for rabbits to eat will attract more rabbits to the area, which puts pressure on the grass, so it dies back, so the decreased food supply leads to a decrease in population because of death or out migration, which takes away the pressure on the grass, which leads to more growth and a good supply of food which leads to a more rabbits attracted to the area which puts pressure on the grass and so on
anthropogenic (human) causes of climate change
- burning of fossil fuels - deforestation (reduction in photosynthesis, burning of biomass, breakdown of organic matter in biomass and soil) - cattle ranching (cows releasing methane) - rice farming in padi fields (anoxic conditions allow growth of methanogens) - use of fertilisers (breakdown of nitrogen-rich compounds)
what are the greenhouse gases?
- carbon monoxide, - carbon dioxide - methane - sulphur dioxide, nitrous oxide - water vapour - ozone.
what is eccentricity (milankovtich cycle)?
- eccentricity is the path of the Earth around the sun. this varies from being a circle, to being an ellipse. - a complete cycle occurs about every 100,000 years
what is global dimming?
- global dimming is probably due to the increased presence of aerosol particles in the atmosphere caused by human action. - aerosols and other particulates absorb solar energy and reflect sunlight back into space. the pollutants can also become nuclei for cloud droplets. - water droplets in clouds coalesce around the particles. increased pollution causes more particulates and thereby creates clouds consisting of a greater number of smaller droplets. - the smaller droplets make clouds more reflective, so that more incoming sunlight is reflected back into space and less reaches the Earth's surface. - this same effect also reflects radiation from below, trapping it in the lower atmosphere (positive feedback).
more examples of positive feedbacks
- melting permafrost - vanishing artic ice - warming wetland peat - amazon rainforest die off - clogging the ocean sink - subsea floor methane hydrate
how does methane gas release link to a positive feedback loop?
- methane is a gas trapped in frozen peat bogs, permafrost and as "water ice" (hydrates) under sediment on the sea floor. - if the atmospheric temperature and ocean temperature increases, the peat bogs and hydrates will thaw and release methane. - this will cause greater warming and the release of more methane
example of a positive feedback
- polar ice reflects light from the sun. as this ice begins to melt, less sunlight gets reflected into space. it is instead absorbed into the oceans and land, raising the overall temperature, and fuelling further melting. - this results in a positive feedback loop called ice albedo feedback, which causes the loss of the sea ice to be self-compounding. - the more it disappears, the more likely it is to continue to disappear.
what is the precession (milankovtich cycle)?
- precession describes a natural 'wobble' of the Earth' axis. this affects the time of seasons as the earth orbits the sun. - the complete wobble cycle takes about 26,000 years.
what is the reflective value of ice?
- sea: 0.3-0.45 - glacier: 0.2-0.4
what is the reflective value of ocean water?
- small zenith angle: 0.03-0.1 - large zenith angle: 0.1-1
explain energy balance between solar radiation and long wave radiation
- the earth has a natural temperature control system. - certain atmospheric gases are critical to this system and are known as greenhouse gases. - on average, about one third of the solar radiation that hits the earth is reflected back to space. - of the remainder, some is absorbed by the atmosphere but most is absorbed by the land and oceans. - the Earth's surface becomes warm and as a result emits infrared radiation. - the greenhouse gases trap the infrared radiation, thus warming the atmosphere - naturally occurring greenhouse gases include water vapour, carbon dioxide, ozone, methane and nitrous oxide, and together create a natural greenhouse effect. - however, human activities are causing greenhouse gas levels in the atmosphere to increase.
what is the axial tilt (milankovtich cycle)?
- the earth's axis tilts. sometimes it is more upright, and sometimes more on its side. - the greater the tilt, the greater the solar radiation the poles receive
explain energy balance
- the energy balance is the balance between incoming energy from the sun and outgoing energy from the atmosphere. energy released from the sun is in the form of shortwave radiation. the earth releases long wave radiation. - when the sun's energy reaches the earth some is reflected back by clouds, some is absorbed or scattered by the atmosphere, some is reflected by the earth, but the majority is still absorbed by the earth. - the amount of energy reflected by the earth is affected by surfaces' albedo - the earth-atmosphere energy balance is achieved as the energy received from the sun balances the energy lost from the earth back into space. by maintaining a balance we enjoy a stable climate. - however, by altering the balance of energy we can cause climate changes. at the moment the world is experiencing global warming which is believed to be caused by the increase amount of greenhouse gases in the atmosphere causing more reflected and released energy to be trapped in the earth's atmosphere.
describe the greenhouse effect
- the greenhouse effect acts as a kind of blanket. - as energy is reflected or released by the earth it moves into the atmosphere where it is trapped and reflected back by a layer of greenhouses gases. - the reflected energy returns to earth and is absorbed warming global temperatures
what is the sunspot cycle?
- the number of sunspots increases from minimum to maximum to minimum on a cycle of about 11 years. - the more sunspots, the more solar flares, and the more heat given off.
what is the problem with the enhanced greenhouse effect?
- the problem of global warming is caused by humans enhancing the greenhouse effect. - we are releasing more greenhouse gases into the atmosphere which is trapping an ever increasing amount of reflected or released energy which returns to earth and warms us further
natural causes of climate change
- variations in solar output (sunspots) - solar or astronomical forcing (milankovitch cycle) - volcanic emmisions - global dimming - cosmic collisions (impact can throw up a lot of debris, block sunlight, prevent photosynthesis, collapsing dinosaur's food chain)
how can volcanic eruptions lead to global dimming?
- volcanic eruptions should increase global temperatures but normally they don't. - this is because they also release large quantities of sulphur dioxide (SO₂). - sulphur dioxide mixes with water vapour to become a volcanic (sulphate) aerosol. - volcanic aerosols reflect the sunlight away and reduce the sun's heat energy entering the atmosphere
how can volcanic eruptions lead to global warming?
- when volcanoes erupt they can produce huge amounts of carbon dioxide. - this carbon dioxide adds to the amount of greenhouse gases in the atmosphere. - this in turn could lead to higher temperatures.
what percentage of the atmosphere is oxygen?
21%
what's the earth average albedo?
34%
what percentage of the atmosphere is nitrogen?
78%