Theory

Question 1

What is the Earth’s energy budget?

Answer 1

It is determined by energy input from the sun (solar radiation) and energy loss to space by thermal or terrestrial radiation, which is emitted from Earth itself.

Question 2

What is the difference between electromagnetic radiation emitted by the sun and that emitted by the earth?

Answer 2

Solar radiation has shorter wavelengths than terrestrial radiation because the sun is hotter.

Question 3

What is electromagnetic radiation?

Answer 3

Electromagnetic radiation are waves of electric and magnetic fields that can travel through vacuum and matter at the speed of light.

Question 4

What is a photon?

Answer 4

In 1905, Einstein showed that electromagnetic radiation has particle properties. In modern quantum physics the light particle is called a photon.

Question 5

Which has shorter and which longer wavelengths: ultraviolet, visible light or infrared?

Answer 5

Infrared has longer wavelengths, then comes visible light and then ultraviolet, which has the shortest wavelengths.

Question 6

Which wavelengths photon between infrared, visible light, and ultraviolet has the highest/lowest energy?

Answer 6

Shorter wavelengths have higher energy, therefore ultraviolet wavelengths have higher energy, followed by visible light, and last infrared with the lowest energy.

Question 7

How does electromagnetic radiation interact with matter?

Answer 7

Interaction of electromagnetic radiation with matter depends on the wavelength of the radiation.

Molecules have different discrete energy states and they can transition from one state to another by absorbing or emitting a photon at a wavelength that corresponds to that energy difference.

Absorption of a photon leads to a transition from lower to higher energy state - the photon once absorbed is gone and its energy is added to that of the molecule.

Emission of a photon leads to a transition from higher to lower energy state - the emitted photon can have a different wavelength than the absorbed one.

Question 8

What is a black body?

Answer 8

A blackbody is an idealized object that can absorb and emit radiation at all frequencies. It emits radiation according to Planck’s law.

Basically, it absorbs 100% of the radiant energy striking it and, if it’s in equilibrium with its surroundings, it emits all the radiant energy as well.

Question 9

What are the differences between the blackbody radiation curves for the sun and earth?

Answer 9

The sun’s blackbody radiation curve has shorter wavelengths, therefore higher intensity and higher energy output. The curve of the sun peaks in the visible part of the electromagnetic spectrum.

The earth’s blackbody radiation curve shows longer wavelengths, therefore less intensity and lower energy output. The curve is completely in the infrared.

Question 10

What is the Stefan-Boltzmann law?

Answer 10

States that the total radiant heat power (irradiance) emitted by a surface is proportional to the fourth power of its absolute temperature. If E is the radiant heat energy emitted from a unit area in one second (that is, the power from a unit area) and T is the absolute temperature (in kelvins), then E = σT4, the Greek letter sigma (σ) representing the constant of proportionality, called the Stefan-Boltzmann constant. This constant has the value 5.670374419 × 10−8 watt per metre2 per K4. The law applies only to blackbodies, theoretical surfaces that absorb all incident heat radiation.

Question 11

What is temperature?

Answer 11

Temperature is the macroscopic expression of the molecular motion in a substance. In any substance, like an ideal gas, molecules are in constant motion. When they bump into each other they exchange energy. The can move faster or slower, it is the average velocity that determines temperature. The faster they move, the higher the temperature. At absolute zero temperature, there is no motion.

Question 12

What are greenhouse gases?

Answer 12

Gases contained in the atmosphere that absorb infrared radiation, so radiation emitted by the earth. The most important greenhouse gases are water vapor and Co2.

This happens because they are molecules made of different elements, which have dipole moments and can interact with electromagnetic radiation.

Question 13

What is the greenhouse effect?

Answer 13

Absorption of radiation by the atmosphere tends to increase its temperature, viceversa emission tends to decrease it. At equilibrium the atmosphere will emit just as much energy as it absorbs, but it will emit radiation in all directions: half of which downward towards the earth, increasing the heat flux of the atmosphere. This additional heat flux from the atmosphere that warms the surface is the greenhouse effect.

The greenhouse effect is like a blanket that keeps the earth warm by reducing heat loss.

Question 14

What is Total Solar Irradiance?

Answer 14

It is the flux of solar radiation through a plane perpendicular to the sun’s rays.

More precisely, it is the amount of total energy emitted by the sun at all wavelengths (not just visible light), falling each second on a 1 square meter perpendicular plane outside of the earth’s atmosphere.

Irradiance on the Earth’s surface additionally depends on the tilt of the measuring surface, the height of the sun above the horizon, and atmospheric conditions. Solar irradiance affects plant metabolism and animal behavior.It

Question 15

What is climate sensitivity?

Answer 15

Climate sensitivity is a measure of how much the Earth’s climate will cool or warm after a change in the climate system, such as how much it will warm for doubling in carbon dioxide (CO2) concentrations. In technical terms, climate sensitivity is the average change in the Earth’s surface temperature in response to changes in radiative forcing, which is the difference between incoming and outgoing energy on Earth. Climate sensitivity is a key measure in climate science, and a focus area for climate scientists, who want to understand the ultimate consequences of anthropogenic global warming.

Question 16

What is climate forcing?

Answer 16

Climate forcing is the physical process of affecting the climate on the Earth through a number of forcing factors. These factors are specifically known as forcings because they drive the climate to change, and it is important to note that these forcings exist outside of the existing climate system.

Examples of some of the most important types of forcings include: variations in solar radiation levels, volcanic eruptions, changing albedo, and changing levels of greenhouse gases in the atmosphere. Each of these are considered external forcings because these events change independently of the climate, perhaps as a result of changes in solar activity or human-caused fossil fuel combustion.

Question 17

What is climate feedback?

Answer 17

Climate feedback is a process that will either amplify or reduce climate forcing. For example, as more ice melts due to global warming, there will be less sunlight reflected away (see albedo) and consequently, surface temperatures will increase.

Forcing denotes an external influence on a characteristic of the climate system. Example: Increased emission from the sun leads to an increase of the temperature.

Feedback denotes the reaction of the (climate) system to the forcing which, in return, leads to a change in the forcing. Example: a change in the Earth’s temperature may cause effects that lead to more radiation being absorbed or emitted. This then creates further changes in the Earth’s temperature. This ‘loop’ where a change in temperature creates a further change is called a climate feedback, or simply feedback.

Question 18

What is the Claus - Clapeyron relation?

Answer 18

The Claus-Clapeyron relation describes the amount of water vapor (in g water per kg of moist air) that air saturation can hold as a function of temperature. The relevance to climatology is that the water-holding capacity of the atmosphere increases by about 7% for every 1 °C (1.8 °F) rise in temperature.

Question 19

Name the different types of feedback processes.

Answer 19

Water vapor feedback: water vapor itself cannot force changes in the climate, due to its short atmospheric lifetime, but atmospheric water vapor concentrations respond to and amplify temperature changes.

Ice-albedo feedback: a positive feedback climate process where a change in the area of ice caps, glaciers, and sea ice alters the albedo and surface temperature of a planet. Ice is very reflective, therefore some of the solar energy is reflected back to space.

Cloud feedbacks: no clearly understood mechanism has been identified that would make an unambiguous prediction of how clouds would change in a warmer climate. This feedback is the least well understood and the most uncertain element.

Question 20

Explain Planck’s law

Answer 20

In 1900, Max Planck pustulated that the electromagnetic energy is emitted not continuously (like by vibrating oscillators), but by discrete portions or quants. Quantum mechanics was born.

Light is emitted in quants and can be considered not only as a wave-like entity but also as a particle, or photon, with the energy given by the Planck Einstein relation

Question 21

What is climate variability?

Answer 21

Climate, unlike the weather, doesn’t change day-to-day because it is based on longer time scales and averages (at least 30 years). However, climate is variable as well.

Climate variability is the way aspects of climate (such as temperature and precipitation) differ from an average. Climate variability occurs due to natural and sometimes periodic changes in the circulation of the air and ocean, volcanic eruptions, and other factors.

The most information about the temporal variations of a parameter over a given time period is provided by a plot of the frequency of occurrence, or the number of observations in a given time interval. The average, standard deviation, and the maximum and minimum values are also given. Plotting the mean over time allows us to quickly identify fluctuations in time.

Question 22

What are temporal scales of variability?

Answer 22

AMO: Atlantic Multidecadal Oscillation - average temperature of the surface of the North Atlantic Ocean. While there is some support for this mode in models and in historical observations, controversy exists with regard to its amplitude, and whether it has a typical timescale and can be classified as an oscillation. There is also discussion on the attribution of sea surface temperature change to natural or anthropogenic causes, especially in tropical Atlantic areas important for hurricane development. The Atlantic multidecadal oscillation is also connected with shifts in hurricane activity, rainfall patterns and intensity, and changes in fish populations.

ENSO: The El Niño–Southern Oscillation (ENSO) is the strongest year-to-year climate fluctuation on the planet. It is spawned in the tropical Pacific Ocean, but its societal and environmental impacts are felt worldwide. The character of ENSO, which is a naturally occurring phenomenon alternating between warm (El Niño) and cold (La Niña) phases, depends on the background climatic conditions in which it develops.

Question 23

What is a Stommel diagram?

Answer 23

A Stommel diagram is used to categorise climate and weather events of different temporal and spatial scales. Logarithmic axes describe time period and size; contours (coloured areas) depict the spectral intensity of variation in the atmosphere.

Microscale: smallest scales to describe features generally of the order 2 km or smaller
Mesoscale: scale for describing atmospheric phenomena having horizontal scales ranging from a few to several hundred kilometres
Synoptic: largest scale used to describe meteorological phenomena, typically high hundreds or 1000 km or more

Question 24

What is variance?

Answer 24

Variance refers to how much a certain process can change from the means. Variance in the graph increases when a phenomenon reaches a higher point on the graph. A process with higher variance contributes more to the variability of the climate system than a process that has low variance.

Question 25

Explain the Milankovitch Cycle

Answer 25

There have been dramatic changes to our climate, the ice ages have come and gone, and there is a strong pattern that explains why ice ages come and go. Milankovitch cycle explains how the earth’s climate changes over hundreds of thousands of years.
The climate is strongly affected by how much sunlight hits the northern latitudes during the summer.
This amount changes based on changes in the earth’s orbit and rotation.

Why are the northern latitudes so important? Because there is more ice in the northern hemisphere, because there is more land. The ice in the northern latitudes reflects sunlight (albedo), creating a positive feedback loop: ice forms when it’s cold. More ice that reflects away light,makes it even colder.

Land has a lower heat capacity than water, which means that water doesn’t change temperature as easily as land. That’s why ice generates more easily on land.

During the winter, the northern hemisphere develops a lot of ice, which, in the summer season, melts. This depends on how much sunlights hits the northern hemisphere during this season. The amount of sunlight is not always the same, and Milankovitch demonstrated how over hundreds of thousands of years the amount of summer sunlight can shift plus or minus 15%. This can bring or end ice ages.

How come the amount of summer sunlight is changing?

The distance between the sun and earth is changing: the earth’s orbit is not a circle, but an ellipse. 4th of July is Aphelion, the day in which the earth is farthest away from the sun. On January 3rd, or Perihelion, it is closest to the sun. Saturn and Jupiter both nudge the earth causing its orbit to shift slightly and become more or less oval (over hundreds of thousands of years).
The earth’s tilt is changing: other objects influence the tilt of the earth gravitationally every 41thousands of years it tilts up or down. When the earth is more tilted it gets more sunlight in the summer, which means more ice is melted and less light is reflected away. This brings a warmer climate. The earth doesn’t tilt much because the moon stabilizes its tilt. Mars has two tiny moons and therefore its tilt changes much more dramatically.

The amount of summer sunlight is affected by three long-term cycles:

1. Axis tilt
2. Eccentricity (orbit)
3. Precession: changes how the distance to the sun matches with the change of the seasons.

Question 26

What is the Ozone-oxygen cycle?

Answer 26

The ozone–oxygen cycle is the process by which ozone is continually regenerated in Earth’s stratosphere, converting ultraviolet radiation (UV) into heat. In 1930 Sydney Chapman resolved the chemistry involved. The process is commonly called the Chapman cycle by atmospheric scientists.

Most of the ozone production occurs in the tropical upper stratosphere and mesosphere. The total mass of ozone produced per day over the globe is about 400 million metric tons. The global mass of ozone is relatively constant at about 3 billion metric tons, meaning the Sun produces about 12% of the ozone layer each day.

Why is the ozone whole more dangerous in the poles even though rays of the sun hit harder on the tropics? This is because Ozone concentrates on the poles, due to the fact that the
ozone moves in a circular way towards the poles where it accumulates.

Question 27

Explain atmospheric stability.

Answer 27

When discussing stability in atmospheric sciences, we typically think about air parcels, or imaginary blobs of air that can expand and contract freely, but do not mix with the air around them or break apart. The key piece of information is that movement of air parcels in the atmosphere can be estimated as an adiabatic process. Adiabatic processes do not exchange heat and they are reversible.

For determining the atmospheric stability we compare the temperature of the air parcel with the temperature of the atmosphere.

Unstable = Tparcel > Tair
The parcel is warmer than its surroundings, so it tends to rise and expand.

Stable = Tparcel < Tair
The parcel is cooler than its surroundings, so it tends to sink and compress (with an oscillatory movement)

Neutral = Tparcel = Tair
The parcel has the same temperature as its surroundings, so no change.

Question 28

What does Buoyancy of water mean?

Answer 28

Buoyancy, or upthrust, is an upward force exerted by a fluid that opposes the weight of a partially or fully immersed object. It’s the equivalent of gravity for liquids.

Question 29

What are the different layers of the atmosphere?

Answer 29

The atmosphere can be divided into layers based on its temperature. These layers are the troposphere, the stratosphere, the mesosphere and the thermosphere. A further region, beginning about 500 km above the Earth’s surface, is called the exosphere.

Question 30

What is the meaning of Adiabatic?

Answer 30

Occurring without loss or gain of heat

Question 31

What is Geostrophic balance/equilibrium?

Answer 31

Describes a balance between Coriolis and horizontal pressure-gradient forces.

Question 32

What is pressure gradient force?

Answer 32

The pressure-gradient force is the force that results when there is a difference in pressure across a surface. In general, a pressure is a force per unit area, across a surface. A difference in pressure across a surface then implies a difference in force, which can result in an acceleration according to Newton’s second law of motion, if there is no additional force to balance it. The resulting force is always directed from the region of higher-pressure to the region of lower-pressure.

When a fluid is in an equilibrium state (i.e. there are no net forces, and no acceleration), the system is referred to as being in hydrostatic equilibrium. In the case of atmospheres, the pressure-gradient force is balanced by the gravitational force, maintaining hydrostatic equilibrium.

In Earth’s atmosphere, for example, air pressure decreases at altitudes above Earth’s surface, thus providing a pressure-gradient force which counteracts the force of gravity on the atmosphere.

Question 33

Explain Geostrophic wind.

Answer 33

A wind that is a balance between the Pressure Gradient Force and the Coriolis Force. The geostrophic wind is directed parallel to isobars (lines of constant pressure at a given height). This balance seldom holds exactly in nature. The true wind almost always differs from the geostrophic wind due to other forces such as friction from the ground.

Question 34

Explain cyclostrophic wind.

Answer 34

Cyclostrophic wind, wind circulation that results from a balance between the local atmospheric pressure gradient and the centrifugal force.

Question 35

What is Transient Climate Response?

Answer 35

The change in the global mean surface temperature, averaged over a 20-year period, centered at the time of atmospheric carbon dioxide doubling, in a climate model simulation” in which the atmospheric CO2 concentration is increasing at 1% per year.

Question 36

What is wind stress?

Answer 36

Wind stress is the shear stress exerted by the wind on the surface of large bodies of water. When wind is blowing over a water surface, the wind applies a wind force on the water surface. The wind stress is the component of this wind force that is parallel to the surface per unit area. Also, the wind stress can be described as the flux of horizontal momentum applied by the wind on the water surface.

The wind stress causes a deformation of the water body whereby wind waves are generated. Also, the wind stress drives ocean currents and is therefore an important driver of the large-scale ocean circulation.

Question 37

Explain Ekman transport.

Answer 37

The speed and direction of the moving water changes with depth. Ocean water at the surface moves at an angle to the wind, and the water under the surface water turns a bit more, and the water below that turns even more. This makes a spiral of moving water 100 to 150 meters (330 to 500 ft) deep called an Ekman spiral. The average direction of all this turning water is about a right angle from the wind direction. This average is Ekman transport.

The Ekman spiral and Ekman transport are named for Swedish scientist V. Walfrid Ekman who first described the spiral in 1905.

Question 38

What are boundary currents?

Answer 38

Boundary currents are ocean currents with dynamics determined by the presence of a coastline, and fall into two distinct categories: western boundary currents and eastern boundary currents.

Eastern boundary currents are relatively shallow, broad and slow-flowing. They are found on the eastern side of oceanic basins (adjacent to the western coasts of continents). Subtropical eastern boundary currents flow equatorward, transporting cold water from higher latitudes to lower latitudes; examples include the Benguela Current, the Canary Current, the Humboldt Current, and the California Current. Coastal upwelling often brings nutrient-rich water into eastern boundary current regions, making them productive areas of the ocean.

Western boundary currents may themselves be divided into sub-tropical or low-latitude western boundary currents. Sub-tropical western boundary currents are warm, deep, narrow, and fast-flowing currents that form on the west side of ocean basins due to western intensification. They carry warm water from the tropics poleward. Examples include the Gulf Stream, the Agulhas Current, and the Kuroshio Current. Low-latitude western boundary currents are similar to sub-tropical western boundary currents but carry cool water from the subtropics equatorward. Examples include the Mindanao Current and the North Brazil Current.

Question 39

What is the relation between salinity and density of water?

Answer 39

When salt is dissolved in fresh water, the density of the water increases because the mass of the water increases. Salinity describes how much salt is dissolved in a sample of water. The more salt there is dissolved in the water, the greater its salinity. When comparing two samples of water with the same volume, the water sample with higher salinity will have greater mass, and it will therefore be more dense.

Question 40

Explain the scientific method

Answer 40

The scientific method was first outlined by Sir Francis Bacon (1561-1626) to provide logical, rational problem solving across many scientific fields.

The basic steps of the scientific method are:

1. Make an observation that describes a problem
2. Create a hypothesis
3. Test the hypothesis,
4. Draw conclusions and refine the hypothesis

The major precepts of the scientific method employed by all scientific disciplines are verifiability, predictability, falsifiability, and fairness. Critical thinking is a key component of the scientific method. Without it, you cannot use logic to come to conclusions.

Question 41

What is the Zeroth law of thermodynamics?

Answer 41

The zeroth law says that when two objects at thermal equilibrium are in contact, there is no net heat transfer between the objects; therefore, they are the same temperature.

Question 42

How is heat transferred?

Answer 42

Heat is transferred through:

• Conduction (typical of solids): physical contact
• Convection (typical of fluids and gases): driven by density
• Radiation: transfer of energy of any object in the form of electromagnetic waves, dependent on its temperature. Does not require matter → It is the way heat is transferred through space

Question 43

How is the average temperature of the Earth calculated?

Answer 43

Earth is not a Black Body. Therefore, the Stefan-Boltzmann law is not ideal to calculate average temperature of the earth. Albedo must be factored in, as well as greenhouse gases contained in the atmosphere.

In research, to get a complete picture of Earth’s temperature, scientists combine measurements from the air above land and the ocean surface collected by ships, buoys and sometimes satellites, too.

The temperature at each land and ocean station is compared daily to what is ‘normal’ for that location and time, typically the long-term average over a 30-year period. The differences are called an ‘anomalies’ and they help scientists evaluate how temperature is changing over time.

A ‘positive’ anomaly means the temperature is warmer than the long-term average, a ‘negative’ anomaly means it’s cooler.

Daily anomalies are averaged together over a whole month. These are, in turn, used to work out temperature anomalies from season-to-season and year-to-year.

Question 44

What is the composition of the atmosphere?

Answer 44

The atmosphere is composed of a complex mixture of gases in which many suspended substances float, such as liquid and solid water (clouds, precipitation), dust and aerosols.

Permanent gases: Nitrogen (about 78.08% by volume), Oxygen (about 20.95% by volume) and Argon (about 0.93% by volume), are almost uniformly distributed and are almost constant in time.

Variable gases: carbon dioxide (current average concentration concentration: about 0.0385% by volume), methane, ozone, aerosols, are present in more variable quantities in space and time. Finally, there is water vapor, whose concentration varies so much that it is hard to estimate an average (in principle, the content of water vapor in the atmosphere oscillates between 0 and 5-6%, with variations that can be very accentuated, both in space and in time).

Question 45

What are normal or dangerous levels of CO2 in the atmosphere?

Answer 45

250 - 400 ppm is normal outdoors
400 - 1.000 typical indoors
5.000 workplace exposure limit in most jurisdictions
40.000 may lead to serious oxygen deprivation and permanent brain damage

current level of CO2 in the atmosphere: 412 ppm

Question 46

What past climates are good examples of future scenarios?

Answer 46

Mid-pliocene: Ice sheets, but smaller than today’s, CO2 atm was similar to present (around 400 ppmv), global mean surface temperature possibly 1.8-3.6 °C warmer than today → but drying and cooling, high sea levels.

Eocene: no or little ice, temperature at equator not very different from poles (global mean surface temperature possibly about 10-16 °C warmer than today), high precipitation, CO2 atm was about 1,400 ppmv.

Question 47

Explain the ideal gas law

Answer 47

Fundamental law of physics, applicable to noble gases. An equation that links Temperature (T), volume (V) and pressure (P).

The ideal gas law is often written in an empirical form:
PV=nRT
where P, V and T are the pressure, volume and temperature; n is the amount of substance; and R is the ideal gas constant.

Temperature, volume, and pressure are interrelated. If you change temperature, and keep volume stable, you can calculate pressure. If one variale changes, the other two also change.

Question 48

What is matter?

Answer 48

In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume.

Question 49

What is the difference between mass and weight?

Answer 49

In scientific contexts, mass is the amount of “matter” in an object, whereas weight is the force exerted on an object by gravity.

Question 50

What is spectral solar irradiance?

Answer 50

The primary source of energy to the Earth is radiant energy from the Sun. This radiant energy is measured and reported as the solar irradiance. When all of the radiation is measured it is called the Total Solar Irradiance (TSI); when measured as a function of wavelength it is the spectral irradiance.

Question 51

What are solar flares?

Answer 51

A solar flare is a tremendous explosion on the Sun that happens when energy stored in ‘twisted’ magnetic fields (usually above sunspots) is suddenly released.

In a matter of just a few minutes they heat material to many millions of degrees and produce a burst of radiation across the electromagnetic spectrum, including from radio waves to x-rays and gamma rays.

Scientists classify solar flares according to their brightness in the x-ray wavelengths. There are three categories: X-class flares are big; they are major events that can trigger radio blackouts around the whole world and long-lasting radiation storms in the upper atmosphere.

M-class flares are medium-sized; they generally cause brief radio blackouts that affect Earth’s polar regions. Minor radiation storms sometimes follow an M-class flare.

Compared to X- and M-class events, C-class flares are small with few noticeable consequences here on Earth.

Question 52

What are coronal mass ejections?

Answer 52

CMEs are huge bubbles of gas threaded with magnetic field lines that are ejected from the Sun over the course of several hours. Although some are accompanied by flares, it is now known that most CMEs are not associated with flares.

This has important implications for understanding and predicting the effects of solar activity on the Earth and in space. If a CME collides with the Earth, it can excite a geomagnetic storm.

Large geomagnetic storms have, among other things, caused electrical power outages and damaged communications satellites. The energetic particles driven along by CMEs can be damaging to both electronic equipment and astronauts or passengers in high-flying aircraft.

Question 53

What is alkalinity of water?

Answer 53

The alkalinity of water is a measure of how much acid it can neutralize. If any changes are made to the water that could raise or lower the pH value, alkalinity acts as a buffer, protecting the water and its life forms from sudden shifts in pH value. This ability to neutralize acid, or H+ ions, is particularly important in regions affected by acid rain.

What affects alkalinity?

Total alkalinity is affected by environmental factors; rain, acidic sanitizers, addition of fill water and other product applications can all change the alkalinity over time. Most alkalinity in surface water comes from calcium carbonate, CaCO3, being leached from rocks and soil. This process is enhanced if the rocks and soil have been broken up for any reason, such as mining or urban development. Limestone contains especially high levels of calcium carbonate and when used to decrease acidity in homes can runoff into surface waters and increase alkalinity. Alkalinity is significant in the treatment of wastewater and drinking water because it will influence treatment processes such as anaerobic digestion. Water may also be unsuitable for use in irrigation if the alkalinity level in the water is higher than the natural level of alkalinity in the soil.

Question 54

How do aerosols affect the climate?

Answer 54

Aerosols influence climate in two primary ways: by changing the amount of heat that gets in or out of the atmosphere, or by affecting the way clouds form.

Some aerosols, like many kinds of dust from ground-up rocks, are light-colored and even a little bit reflective. When the sun’s rays beam down on them, they bounce the rays back out of the atmosphere, preventing that heat from ever reaching Earth’s surface.

But other aerosols, like little flecks of black carbon from burned coal or wood, do the opposite, absorbing heat from the sun as it beats down. That ends up warming the atmosphere, though it cools the surface of the Earth by preventing the heat from escaping. Overall, that effect is probably smaller than the cooling most aerosols induce—but it’s far from nonexistent, and the more carbon-based material that collects in the atmosphere, the more warming the atmosphere experiences.

Aerosols also influence how clouds form and grow. Water droplets coalesce readily around particles, so a particle-rich atmosphere promotes cloud formation. White clouds reflect incoming sun, preventing it from getting to the surface and warming land or water—but they also absorb the heat that the planet is constantly emitting back outward, trapping it in the lower atmosphere. Depending on the cloud type and location, they can either warm their surroundings or cool them.

Question 55

How do volcanic eruptions affect the climate?

Answer 55

Volcanoes can impact climate change. During major explosive eruptions huge amounts of volcanic gas, aerosol droplets, and ash are injected into the stratosphere. Injected ash falls rapidly from the stratosphere – most of it is removed within several days to weeks – and has little impact on climate change. But volcanic gases like sulfur dioxide can cause global cooling, while volcanic carbon dioxide, a greenhouse gas, has the potential to promote global warming.

The most significant climate impacts from volcanic injections into the stratosphere come from the conversion of sulfur dioxide to sulfuric acid, which condenses rapidly in the stratosphere to form fine sulfate aerosols. The aerosols increase the reflection of radiation from the Sun back into space, cooling the Earth’s lower atmosphere or troposphere.

Question 56

Define extreme events.

Answer 56

An extreme event is a time and place in which weather, climate, or environmental conditions—such as temperature, precipitation, drought, or flooding—rank above a threshold value near the upper or lower ends of the range of historical measurements. Though the threshold is subjective, some scientists define extreme events as those that occur in the highest or lowest 5% or 10% of historical measurements. Other times they describe events by how far they are from the mean, or by their recurrence interval or probability.

Question 57

What are the main types of clouds?

Answer 57

While clouds appear in infinite shapes and sizes they fall into some basic forms. From his Essay of the Modifications of Clouds (1803) Luke Howard divided clouds into three categories; cirrus, cumulus and stratus.

Cirro-form
The Latin word ‘cirro’ means curl of hair. Composed of ice crystals, cirro-form clouds are whitish and hair-like. There are the high, wispy clouds to first appear in advance of a low-pressure area such as a mid-latitude storm system or a tropical system such as a hurricane.

Cumulo-form
Generally detached clouds, they look like white fluffy cotton balls. They show vertical motion or thermal uplift of air taking place in the atmosphere. They are usually dense in appearance with sharp outlines. The base of cumulus clouds are generally flat and occurs at the altitude where the moisture in rising air condenses.

Strato-form
From the Latin word for ‘layer’ these clouds are usually broad and fairly wide spread appearing like a blanket. They result from non-convective rising air and tend to occur along and to the north of warm fronts. The edges of strato-form clouds are diffuse.

Nimbo-form
Howard also designated a special rainy cloud category which combined the three forms Cumulo + Cirro + Stratus. He called this cloud, ‘Nimbus’, the Latin word for rain. The vast majority of precipitation occurs from nimbo-form clouds and therefore these clouds have the greatest vertical height.