Apply Greenhouse Effect - IB Physics

The thawing of Arctic permafrost is observed to release large quantities of methane, a potent greenhouse gas. This leads to further atmospheric warming, which in turn accelerates the thawing of permafrost. How is this cycle best described?
Answer: A positive feedback loop, because an initial warming triggers a process that causes additional warming. This is a classic example of a positive feedback loop in the climate system. The initial change (warming) causes a secondary effect (permafrost thaw and methane release) that amplifies the initial change (more warming). A negative feedback loop would counteract the initial change. Choice A is incorrect because while methane has a finite lifetime, its immediate effect is to amplify warming. Choice C is incorrect; the initial warming is the forcing, while the permafrost response is a feedback. Choice D completely misuses the term 'resonance' in this context.
Which statement best distinguishes the enhanced greenhouse effect from the natural greenhouse effect?
Answer: The enhanced effect refers to the additional warming caused by anthropogenic emissions of greenhouse gases above their natural levels. The natural greenhouse effect is the baseline warming caused by naturally occurring greenhouse gases. The 'enhanced' greenhouse effect refers specifically to the amplification of this natural effect due to human activities (anthropogenic emissions) increasing the concentration of these gases (like CO₂, CH₄, N₂O) and introducing new ones (like CFCs). Choice A is incorrect as CO₂ and H₂O are major contributors to both effects. Choice B is incorrect; both effects concern infrared radiation, not UV (which is related to the ozone layer). Choice D is too absolute; the natural climate also experiences shifts and contains feedback loops.
In the process of the greenhouse effect, greenhouse gas molecules absorb and re-radiate longwave radiation. What is the principal source of this longwave radiation?
Answer: The Earth's surface, after it has been warmed by absorbing shortwave solar radiation. The process begins with the Earth's surface absorbing shortwave radiation from the sun, which causes the surface to warm up. Any object with a temperature above absolute zero emits thermal radiation. For the temperatures of the Earth's surface, this radiation is in the longwave (infrared) part of the spectrum. It is this outgoing longwave radiation from the surface that is then absorbed by greenhouse gases in the atmosphere. Geothermal heat flux (choices B and D) is several orders of magnitude smaller than the solar energy flux and is not the primary source of the radiation involved. Choice A is an incorrect description of scattering.
A planet's surface is in thermal equilibrium. It absorbs energy from its star and also from its own greenhouse atmosphere (back-radiation). If the concentration of greenhouse gases in its atmosphere increases, what is the immediate effect on the energy balance at the surface and the eventual effect on the surface temperature?
Answer: The back-radiation from the atmosphere increases, causing the surface to warm to a new, higher equilibrium temperature. An increased concentration of greenhouse gases means the atmosphere becomes more effective at absorbing outgoing longwave radiation from the surface and re-radiating it. A significant fraction of this re-radiation is directed back down towards the surface ('back-radiation'). This increases the total energy input to the surface. To restore equilibrium, the surface must radiate more energy, which, according to the Stefan-Boltzmann law (P ∝ T⁴), requires its temperature to rise. Choice B has the effect reversed. Choice C incorrectly identifies the source of the extra energy. Choice D assumes an unsubstantiated change in emissivity.
For a planet with a thick greenhouse atmosphere, radiation escapes to space not from the surface, but from an effective 'emission altitude'. How does an increase in greenhouse gas concentration affect this emission altitude and the planet's energy balance?
Answer: It raises the emission altitude to a higher, colder layer, reducing outgoing radiation and causing warming. Adding more greenhouse gases makes the atmosphere more opaque to infrared radiation. This means that for radiation to escape to space, it must originate from higher up in the atmosphere where the air is thinner. In the troposphere, temperature decreases with altitude. Therefore, the new, higher emission altitude is at a colder temperature. According to the Stefan-Boltzmann law, a colder body radiates less energy. This reduction in outgoing radiation creates a positive energy imbalance (incoming > outgoing), which causes the entire climate system to warm until a new equilibrium is reached. A and D are the opposite of what occurs. C is incorrect because the altitude shift is the key mechanism.
A massive volcanic eruption injects large quantities of both carbon dioxide (a greenhouse gas) and sulfate aerosols into the stratosphere. What is the most likely net effect on the average global surface temperature in the one to two years following the eruption?
Answer: A net cooling, because the aerosols increase the planetary albedo by reflecting solar radiation. While volcanic eruptions do release CO₂, the short-term (1-3 years) climate impact is dominated by the injection of sulfate aerosols into the stratosphere. These aerosols form a haze that reflects incoming solar radiation, increasing the planet's albedo. This reflection of shortwave radiation causes a net cooling effect that is more immediate and pronounced than the warming effect from the added CO₂. Therefore, a temporary global cooling is the most likely outcome. A and D are incorrect. C is incorrect because the two effects are not typically balanced in the short term.
Greenhouse gases like water vapour (H₂O) and methane (CH₄) strongly absorb infrared radiation but are largely transparent to incoming visible light. What is the primary physical reason for this difference?
Answer: The energy of infrared photons corresponds to allowed transitions between molecular vibrational states, while visible light photons have too much energy for these transitions. Molecular energy levels (electronic, vibrational, rotational) are quantized. Infrared photons have energies that match the gaps between vibrational energy levels in greenhouse gas molecules. Visible light photons have much higher energies, corresponding to gaps between electronic energy levels. Since these molecules don't have electronic transitions in the visible range, they are transparent to visible light but absorb IR at their specific vibrational frequencies. Choices B and C are incorrect descriptions of the physical processes. Choice D is close but less precise than A; 'vibrational states' is the key concept from the syllabus.
An infrared photon interacts with a carbon dioxide molecule in the troposphere. Which statement best describes the mechanism by which this interaction contributes to the greenhouse effect?
Answer: The photon's energy matches a vibrational energy level transition in the molecule, causing the molecule to vibrate more intensely and then re-radiate energy. The core mechanism of the greenhouse effect is the resonance absorption of infrared (IR) photons by greenhouse gas molecules. The energy of these photons corresponds to the energy gaps between quantized vibrational states of the molecules. The molecule absorbs the photon, enters an excited vibrational state, and then typically de-excites by re-radiating a photon in a random direction (some back to Earth) or by transferring the energy to other molecules via collision. Choice B describes absorption of higher-energy (UV/visible) photons. Choice C describes rotational transitions, which involve lower-energy (microwave) photons, and is not the primary mechanism. Choice D (ionization) requires much higher energy photons (UV/X-ray).
The warming inside a glass greenhouse is often used as an analogy for the Earth's greenhouse effect. What is a key physical difference in the dominant warming mechanism?
Answer: A glass greenhouse primarily works by physically trapping warm air and preventing convection, while the atmospheric effect is a radiative process. The analogy is somewhat misleading. While glass is transparent to visible light and partially opaque to infrared (a radiative effect), the primary reason a physical greenhouse gets hot is that the glass roof and walls prevent the air inside, which has been heated by the sun-warmed surfaces, from rising and mixing with cooler air outside. It suppresses heat loss by convection. The atmospheric greenhouse effect, in contrast, is fundamentally a radiative phenomenon based on the absorption and re-radiation of infrared energy by gases. Choice A has the radiation type wrong. B is not the dominant difference. D describes the scale, not the mechanism.
If both planets suddenly experience a 10% increase in solar irradiance, which statement best describes the expected temperature response and the underlying physical mechanism?
Answer: Planet B will show a larger temperature increase due to enhanced greenhouse effect amplifying the additional incoming radiation Planet B's thick atmosphere with high greenhouse gas concentration will trap more of the additional thermal radiation from the warmed surface, amplifying the temperature increase. The greenhouse effect scales with both incoming radiation and atmospheric opacity. A is wrong because thermal inertia affects response time, not final equilibrium temperature. C ignores the different atmospheric greenhouse effects. D incorrectly suggests greenhouse saturation at these temperature ranges.
For a planet with a stable atmosphere to be in thermal equilibrium, which condition regarding its overall energy budget must be met?
Answer: The rate of incoming solar radiation absorbed by the planet system must equal the rate of outgoing longwave radiation emitted to space from the top of the atmosphere. For the entire planet-atmosphere system to be in thermal equilibrium, the total energy coming in must equal the total energy going out. The energy coming in is the solar radiation that is not reflected (i.e., is absorbed). The energy going out is the thermal longwave radiation emitted to space from the top of the atmosphere. Choice A is incorrect for a planet with a greenhouse effect, as the surface also receives longwave radiation from the atmosphere and must radiate the sum of the solar energy it absorbs and this atmospheric back-radiation. B and D describe parts of the internal energy transfers but not the overall condition for equilibrium with space.
Carbon dioxide (CO₂) is a linear triatomic molecule and a key greenhouse gas. Which property related to its molecular structure is essential for its ability to absorb infrared radiation?
Answer: Its bending and asymmetric stretching vibrations create a temporary, oscillating electric dipole moment. For a molecule to be infrared-active, it must undergo a change in its electric dipole moment during a vibration. Although CO₂ is symmetric and has no permanent dipole moment when at rest, certain vibrational modes (like bending and asymmetric stretching) distort its symmetry. This distortion creates a temporary, oscillating dipole moment that can interact with the electric field of an incoming IR photon, allowing the photon to be absorbed. Choice A and B are true but are not the reason for IR absorption. Choice D is a physically inaccurate description.
A planet is in a state of radiative equilibrium. A large quantity of a long-lived greenhouse gas is then suddenly added to its atmosphere. Which statement describes the immediate and subsequent changes to the planet's energy budget?
Answer: Incoming radiation immediately exceeds outgoing radiation, causing the planet to warm until a new, hotter equilibrium is reached. The addition of a greenhouse gas makes the atmosphere more opaque to outgoing infrared radiation, immediately reducing the rate at which energy leaves the planet. The incoming solar radiation remains unchanged. This creates an energy imbalance where energy in > energy out. This net gain of energy causes the planet system (oceans, land, atmosphere) to warm. As the system warms, it emits more radiation (Stefan-Boltzmann law). The warming continues until the outgoing radiation increases enough to once again balance the incoming radiation, establishing a new equilibrium at a higher temperature. Choice A has the imbalance reversed. Choice C confuses the effect with that of aerosols. Choice D is incorrect; the adjustment process is not instantaneous and requires a change in temperature.
The absorption of a photon of infrared radiation by a molecule of methane (CH₄) in the atmosphere causes the molecule to transition to a higher energy state. This absorbed energy corresponds primarily to an increase in which type of molecular energy?
Answer: Vibrational energy Molecular energy is quantized into electronic, vibrational, and rotational levels. The energy of infrared photons corresponds to the energy differences between the quantized vibrational states of molecules like methane. When an IR photon is absorbed, the molecule transitions to a higher vibrational state, meaning its atoms vibrate with greater amplitude. Electronic transitions (A) require higher-energy photons (visible or UV). Translational kinetic energy (C) is not quantized in this way. Nuclear binding energy (D) involves processes at vastly higher energies.
A planet with a stable greenhouse gas atmosphere experiences a large-scale event that permanently increases its average surface albedo. What is the long-term consequence for the planet's average surface temperature?
Answer: The temperature will decrease because a smaller fraction of the incident solar radiation is absorbed by the planet's surface. Albedo is the fraction of incident solar radiation that is reflected back to space. If the albedo increases, the planet as a whole absorbs less energy from its star. According to the principle of energy balance, for the planet to reach a new thermal equilibrium, it must radiate less energy. Based on the Stefan-Boltzmann law (P = σAT⁴), a lower power output corresponds to a lower equilibrium temperature. Therefore, the planet's average temperature will decrease. Choice A misunderstands reflection. Choice C incorrectly assumes the greenhouse effect is independent of the initial energy input to the surface. Choice D incorrectly links albedo and emissivity; they are distinct properties.
Two planets, X and Y, are identical except for their surface properties. Planet X has a surface with an average emissivity of 0.9, while Planet Y has a surface with an average emissivity of 0.6. Both have identical, significant greenhouse atmospheres. How will their average surface temperatures likely compare?
Answer: Planet Y will be warmer because with lower emissivity, its surface must reach a higher temperature to radiate away the energy it absorbs. A planet's surface must radiate away the energy it absorbs from its star and from its atmosphere to maintain equilibrium. The power radiated is given by the Stefan-Boltzmann law, P = εσAT⁴. For a given amount of absorbed power P, a surface with a lower emissivity (ε) must have a higher temperature (T) to radiate that same amount of power. Therefore, Planet Y, with the lower emissivity, will have a higher surface temperature. Choice B is flawed because absorptivity equals emissivity, but the key is the temperature required for radiative balance. Choice A uses correct but imprecise reasoning. Choice C is incorrect as emissivity is fundamental to achieving thermal balance.
Earth's atmosphere is composed primarily of nitrogen (N₂) and oxygen (O₂). Why are these gases not significant contributors to the greenhouse effect?
Answer: They are symmetric diatomic molecules whose vibrations do not create a changing electric dipole moment. For a molecule to absorb infrared radiation, it must have a vibrational mode that causes a change in its electric dipole moment. Symmetric diatomic molecules like N₂ and O₂ have no permanent dipole moment, and when they vibrate, their symmetry is preserved, so no oscillating dipole moment is created. Therefore, they cannot interact with and absorb the electromagnetic field of an IR photon. Choice A is factually incorrect; they are diatomic. Choice B misunderstands the mechanism; absorption doesn't break bonds. Choice D is incorrect; these gases are well-mixed throughout the troposphere where the greenhouse effect is strongest.
An exoplanet orbiting a red dwarf star has a dense CO₂ atmosphere. The planet is tidally locked, with one side permanently facing the star and the other in perpetual darkness. How would the greenhouse effect differ between the day and night sides, and what would be the primary mechanism?
Answer: The night side shows stronger greenhouse effect because atmospheric re-radiation becomes the primary heat source in absence of stellar input When analyzing atmospheric effects on tidally locked exoplanets, you need to consider how the greenhouse effect operates differently when stellar radiation is present versus absent. The greenhouse effect works by trapping outgoing thermal radiation from a planet's surface. On the day side of this tidally locked planet, the surface receives continuous stellar heating, so the greenhouse effect supplements but doesn't dominate the energy budget. However, on the night side, atmospheric re-radiation becomes the sole mechanism maintaining surface temperature above what it would be without an atmosphere. Option D correctly identifies that the night side experiences a stronger greenhouse effect because atmospheric absorption and re-emission of thermal radiation is the primary—and only—heat source keeping the surface warm. The dense CO₂ atmosphere absorbs outgoing infrared radiation and re-radiates it back to the surface, creating a significant warming effect. Option A incorrectly suggests the day side has stronger greenhouse effects due to higher thermal emissions, but higher surface temperature actually means the greenhouse effect contributes proportionally less to the total energy budget. Option B wrongly claims the greenhouse effect is negligible on both sides—atmospheric density and composition don't disappear due to temperature differences. Option C assumes uniform effects despite fundamentally different energy sources on each side. For IB Physics exams, remember that greenhouse effect strength isn't just about atmospheric composition—it's about the relative importance of atmospheric heating compared to other energy sources. When direct stellar heating is absent, atmospheric effects become proportionally more significant.
A space mission measures the outgoing longwave radiation from a planet at the top of its atmosphere and finds it to be $180 \ \text{W m}^{-2}$ . The planet receives $720 \ \text{W m}^{-2}$ of solar radiation and has an albedo of 0.4. If this planet achieves thermal equilibrium, what can be concluded about its energy balance?
Answer: The planet is gaining energy and will warm up because absorbed radiation exceeds outgoing radiation Absorbed solar radiation = $720 \times (1 - 0.4) = 432 \ \text{W m}^{-2}$ . Since outgoing longwave radiation is only $180 \ \text{W m}^{-2}$ , there is a net energy gain of $432 - 180 = 252 \ \text{W m}^{-2}$ . The planet will warm until outgoing radiation increases to match absorbed radiation. A incorrectly assumes equilibrium exists. B reverses the energy flow direction. D is wrong because the energy balance can be calculated from the given radiation values.
A planet with a stable atmosphere containing greenhouse gases orbits a star. If the star's luminosity permanently decreases, reducing the solar constant at the planet, what is the consequence?
Answer: The planet will cool until it reaches a new, lower equilibrium temperature where outgoing radiation balances the reduced incoming radiation. The planet's energy budget is driven by incoming solar radiation. If this input decreases, the planet will have a net energy loss (outgoing > incoming) at its original temperature. Consequently, the entire planet-atmosphere system will cool down. As it cools, the outgoing thermal radiation decreases (per Stefan-Boltzmann law). This cooling continues until the outgoing radiation is reduced enough to balance the new, lower level of incoming solar radiation, establishing a new, colder equilibrium. Choice A is incorrect; the greenhouse effect is a passive property of the atmosphere. Choice C assumes an unsubstantiated feedback. Choice D is contradictory; a cooler surface radiates less infrared, so the amount trapped must also decrease.

Start this quiz