unit 4 aos1 enviromental exam

natural and human factors that affect earths energy balance

Both natural and anthropogenic (human) factors affect Earth’s temperature and energy balance. Earth’s energy budget(or balance) is the balance between the energy Earth receives from the Sun and the energy which is radiated back into space.

All of the Earth’s spheres are involved in this balance: the hydrosphere absorbs solar energy and redistributes it with ocean currents across the Earth, ensuring balanced heat flow. The atmosphere counteracts the imbalance, as wind travels along the Earth and gases affect heat flow. The lithosphere re-radiates light variably and the biosphere absorbs solar energy in photosynthesis to be used further along the food chain.

identification of natural phenomena and anthroprogenic factors that affect earths energy balance

• volcanic eruptions

• solar variability

• changes in atmospheric gas composition due to human intereactions

solar variability

The Sun does not radiate heat equally through time. It acts on a roughly 11-year solar cycle.

• Goes through solar maximums, the periods of high activity from the sun and solar minimums, periods of low activity.

• We can see this activity from the presence of sunspots, which are dark spots on the surface of the Sun.

• Sunspots and flares indicate changes in the Sun’s magnetic field, each solar cycle, the Sun’s magnetic field flips, due to the current of hot gas within the Sun, and theSun’s ‘solar dynamo’

• Increase or decrease in solar radiation reaching Earth about 0.1-0.2%

It has been predicted that the solar cycles do have some effect on the weather, the International Panel on Climate Change (IPCC) has concluded that the Sun's solar cycle does not account for global warming.

Solar cycles can affect air and water circulation (i.e. wind patterns, ocean currents) and possibly cloud cover. It has also been observed that ozone concentrations are higher during solar maxima.

Solar flares can cause geomagnetic storms, which are temporary disturbances to Earth’s magnetic systems, which can cause disturbances to satellites, power grids or radio

transmissions. Solar flares are also the cause of the southern and northern lights.

volcanic eruptions

Volcanoes erupt many different molecules, including carbon dioxide (CO2,) sulfur dioxide (SO2,) hydrogen sulfide (H2S) and hydrogen halides, which can be harmful to nearby life depending on their concentrations.

Earth’s active volcanoes release between 180 to 440 million tonnes of CO2 every year.

This CO2 was essential for the formation of life and the natural greenhouse gas effect. It is relatively small compared to human activity which released 36.8 billion tonnes of CO2 in 2019. Even a devastating volcanic eruption would pale in comparison to human emissions.

human activity

Humans contribute to the change in Earth’s atmosphere. Actions which produce greenhouse gases include

• Burning fossil fuels, releasing trapped CO2 from millions of years ago.

• Livestock, which produce CH4 from their metabolism

• Other production of chemicals like CFCs

the natural greenhouse effect

Earth’s temperature is determined by the amount of energy coming in and out of the atmosphere, greenhouse gases are a major factor in changing this ‘budget’

About only 34% of solar energy is reflected directly back into space.

• Another 19% is absorbed by the atmosphere by water vapour, CO2 and other gases.

This is the natural greenhouse gas effect

• Around 47% of the solar energy is received by the surface of the planet (noting that this amount is variable, depending on location and time of year)

• The greenhouse gas effect is ESSENTIAL to life, without it, Earth would be a frozen ball.

Some solar radiation absorbed by Earth is reradiated back into the atmosphere in the form of infrared light (IR), where some of it escapes and some of it is absorbed and reflected towards Earth by natural greenhouse gases such as water vapour, carbon dioxide (CO2), nitrous oxide (N2O), ozone (O3) and methane (CH4).

Water vapour is the most significant greenhouse gas, and is the main natural greenhouse gas.

The Sun emits a variety of radiation, around 38% is visible light (what we interpret as light). 53% is at longer wavelengths (more than 700 nm) at infrared light (which we perceive as heat) and a small amount is ultraviolet light (<390 nm). As this sunlight moves through the atmosphere, molecules absorb different frequencies of light. This is why not all radiation reaches Earth’s surface.

Ozone absorbs most ultraviolet light, most light that reaches the surface is UV and visible light.

BUT THE OZONE LAYER IS NOT THE GREENHOUSE EFFECT!

the albedo effect

Albedo is the fraction of solar energy that is re-radiated from Earth to space. It ranges from a scale of 0 (no reflection) to 1 (all energy reflected). Light surfaces (light in colour) reflect more radiation than dark surfaces do.

Ice and snow have a high albedo, meaning they reflect more light at 0.6-0.9, while water has lower albedo, meaning it's more absorbent and less reflective at 0.1. Earth has an average albedo of 0.31, which is moderately low.

Albedo is important to consider as if we lose high albedo surfaces on Earth, more solar energy is likely to be absorbed by the ground, increasing temperature.

• As Earth warms, ice and snow begin to melt.

• This means that more energy is absorbed and thus the Earth will warm up, causing even more ice and snow to melt.

• This causes a positive feedback loop.

• Scientists are particularly interested in how this will affect Earth’s albedo, if more water vapour from melted ice and snow is present, then more clouds can form, which have a relatively high albedo.

ocean circululation

Oceans store heat and are heat sinks, they distribute heat by ocean currents, both near the surface and deep underwater. This helps to stabilise global climate patterns such as preventing the equator (which receives most of the solar energy) from becoming too hot, and moving this heat towards the poles.

Surface currents are created by wind patterns, the rotation of Earth and the shape of ocean basins.

Earth’s currents ‘deflect’ wind according to the rotation of the Earth and increase their rotational movement. This is the Corialis effect.

• Deepwater currents create ‘thermohaline circulation’ , which is the current caused by the difference in water density. Water density is affected by both heat and salinity thus thermo and haline. Cold water is typically more dense, and saltier water is more dense. The greater the difference in densities, the greater the mixing and circulation.

• Changes in this circulation could lead to unexpected storms, hurricanes, and temperatures around the globe.

This circulates warm and cold water around the globe, accounting for the movement of nutrients and dissolved gases such as carbon dioxide and oxygen.

Ocean currents thus regulate the global climate because they counteract the uneven spread of solar energy coming into Earth. Also, places near water often have milder climates with less drastic temperature shifts due to the water regulating temperature.

carbon sequestration

is the storage of CO2 in carbon sinks, to lessen its effect in the greenhouse gas effect. It is a natural process within the carbon cycle and happens throughout the different spheres.

oceans act as carbon sinks

carbon dioxide in the air dissolves in water to form carbonic acid (H2CO3) which is the process of ocean acidification. However, as more and more CO2 is being held in the ocean, the ocean’s capacity to hold it is decreasing. Cool waters are more effective than warm waters as carbon sinks, and since the water is warming, the rate that oceans can absorb carbon dioxide and their capacity is decreasing.

• Shells are made of calcium carbonate

• CO2 dissolves into water to form carbonic acid.

• Carbonic acid makes the water more acidic by dissolving into H+ ions (pH lower)

• Extra H+ reacts with carbonate ions to reform bicarbonate ions

• Reduces the amount of carbonate ions available for marine life to make shells.

• Less availability of carbonate ions -> harder to form shells -> less survival

• Life in the oceans also plays a role in carbon sequestration, although to a lesser extent.

• Phytoplankton are plants which are the ‘base’ for the aquatic food chain. They take up carbon dioxide during photosynthesis. However, they need light and nutrients.

• Once they die, they sink to the ocean bottom and decompose and eventually form ocean sediment.

forests are also carbon sinks

absorbing CO2 during photosynthesis and then incorporating this carbon into their own structure. This carbon is released during fires (combustion). Carbon is passed down through the carbon cycle, and through plants and animals consuming the living matter.

soil

can also act as a carbon sink, where it is stored as organic matter. It can remain stored like this for long times.

This is why deforestation and the clearing of forests can release CO2, as the trees release their CO2 and the soil is acted upon by decomposers, which release CO2.

The climate, vegetation, soil texture and drainage affect how much carbon is stored and how long the carbon is stored for.

greenhouse effect

The majority of the ‘greenhouse effect’ that we talk about refers to the enhanced greenhouse effect, where human activity has increased the concentration of CO2 in the atmosphere to irregular amounts. This leads to more heat energy being absorbed back to the Earth and thus increasing the global surface temperature.

The natural greenhouse effect regulates an average temperature, which allows for Earth to be as suitable for life as it is. Water vapour is the main gas which contributes to this.

Since the Industrial Revolution (after c. 1750), we began to produce more greenhouse gases through

• The combustion of fossil fuels, releasing carbon dioxide into the atmosphere.

• The expansion of agriculture, which needed more land, which then reduced the abundance of forests to act as carbon sinks

• The manufacturing of artificial greenhouse gases like chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFs)

Not all gases in the atmosphere are greenhouse gases and not all greenhouse gases have the same potency. The ability for a gas to absorb heat is determined by how excited their molecules can get from incoming solar radiation. If a gas molecule has more ways to vibrate, then it can absorb a wider range of frequencies of light and thus a larger amount of energy.

But a gas’ potency is also determined by

• The ability for the gas to absorb heat (as above)

• The length of time it persists (lifetime)

• The concentration within the atmosphere

global warming potential

a measure to compare the impact of different greenhouse gases. The GWP is how much infrared light can be absorbed over a specific timeframe (usually its lifetime) relative to 1 unit of CO2 where CO2 is given a GWP of 1.

• CO2 has a GWP of 1 (standard reference point)

• Methane (CH4) has a GWP of ~28-36 over 100 years, but methane will only last about a decade

• Nitrous oxide (N2O) has a GWP of 265-289 over 100 years.

• That is, one tonne of methane has an equivalent warming ability to 28-36 tonnes of CO2 over 100 years.

similarities between natural and enhanced greenhouse effect

• Both involve the trapping of infrared radiation by greenhouse gases

• Both involve the re-emission of visible light as infrared light and the subsequent trapping by GHGs

• both heat the earth

• Both share the same TYPES of GHGs (not necessarily as their cause) of CO2, methane, water vapour and nitrous oxide.

differences between natural and enhanced greenhouse effects

• The natural greenhouse effect is essential for life, maintaining a livable temperature. The enhanced greenhouse effect is harmful and leads to climate change

• Main gas in natural greenhouse effect is water vapour (and a little CO2) Main gas in enhanced greenhouse effect is CO2

• CFCs, PFCs and other artificial gases contribute to enhanced greenhouse effect not natural greenhouse effect

• Enhanced greenhouse effect is largely because of fossil fuel combustion Natural greenhouse effect is mostly because of natural water vapour (and gases released from life/volcanic eruptions

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