Consider the following statements. a. The temperature of the troposphere generally decreases with increasing altitude. b. The troposphere is heated not by absorption of incoming short wave solar radiation but by transfer of heat from the earth's surface. Now state whether :
- (1)Both the statements are correct and second is the correct explanation of the first
- (2)Neither of the statements is correct
- (3)Both the statements are correct, but the second is not the correct explanation of the first
- (4)The first statement is correct, but second is not the correct
Correct — option (1), both statements a and b are correct, and b is the correct explanation of a. Statement a records the defining feature of the troposphere: temperature falls as altitude rises, at an average environmental lapse rate of about 6.5°C per kilometre, all the way up to the tropopause (roughly 8 km over the poles, 18 km over the equator), where the fall stops and the stratosphere begins. Statement b gives the mechanism that produces exactly this pattern. Incoming short-wave solar radiation passes through the largely transparent atmosphere with only modest direct absorption; it is the earth's solid and liquid surface that absorbs most of that radiation and warms up, and the surface then re-radiates energy as long-wave (terrestrial, infrared) radiation and transfers heat upward into the air immediately above it by conduction, and further up by convection as warmed parcels of air rise. Because the primary heat source is the ground rather than the sun acting directly on the air, the layer of atmosphere closest to the surface is warmest, and air gets progressively cooler the further it sits from that source — which is precisely the decrease in temperature with altitude described in statement a. Since b identifies the actual physical cause of the pattern a describes, b is the correct explanation of a, and option (1) is the only choice that captures both the truth of each statement and the explanatory link between them.
- (2)Neither of the statements is correct — Both statements are standard, well-established atmospheric science, not doubtful claims. The decrease of temperature with altitude in the troposphere (the environmental lapse rate) is a directly measured, textbook fact, and the earth's-surface heating mechanism behind it is equally well established — the atmosphere is heated predominantly from below, by terrestrial radiation and surface heat transfer, not by direct absorption of sunlight passing through it. Declaring both statements wrong ignores basic, settled physical geography.
- (3)Both the statements are correct, but the second is not the correct explanation of the first — This gets the individual truth of both statements right but breaks the causal link between them for no good reason. Statement b is not an unrelated fact sitting alongside statement a — it is the mechanism that produces the very pattern statement a describes. If the atmosphere near the ground receives most of its heat from the surface below rather than from the sun directly, then air further from the surface necessarily receives less of that heat and is cooler, which is exactly the temperature-with-altitude relationship in statement a. Denying the explanatory connection here misses the point the pair of statements is built to test.
- (4)The first statement is correct, but second is not the correct — Statement a is indeed correct, but statement b is not the false one here — it is also correct, and is in fact the mechanism behind statement a. The claim that the troposphere is heated primarily by the earth's surface rather than by direct absorption of incoming short-wave solar radiation is standard physical geography: short-wave radiation passes through the atmosphere with limited absorption, while the surface absorbs strongly and re-radiates long-wave heat upward. Marking this statement false discards a true and important fact.
The troposphere is the lowest layer of the atmosphere, extending from the surface up to the tropopause, and it is where almost all weather occurs. Its defining thermal property is the environmental lapse rate — temperature falling by roughly 6.5°C for every kilometre gained in altitude — and this happens because the troposphere is heated chiefly from below, by the earth's surface, rather than directly by the sun. Incoming short-wave solar radiation is largely transparent to the gases of the lower atmosphere and passes through with comparatively little direct absorption; it is the ground and oceans that absorb the bulk of it, warm up, and then transfer that heat back into the air above by conduction, convection and long-wave (terrestrial) radiation. This 'heated from below' mechanism is why the air closest to the surface is warmest and why temperature declines steadily with height through the troposphere.
This assertion-reason format is a staple of MPSC and UPSC geography sections, and it rewards candidates who understand mechanism rather than just memorising the lapse-rate fact in isolation. A candidate who only knows 'temperature falls with height' but not why can be tempted by option (3) — agreeing both statements are true while wrongly assuming they are unconnected facts — when in truth the second statement is precisely the causal explanation for the first. Understanding this heating mechanism also explains related phenomena examined elsewhere on this paper and others, such as why mountain tops are colder than valley floors at the same latitude, and why the stratosphere (heated instead by ozone's direct absorption of ultraviolet radiation) behaves in the opposite way, warming with height rather than cooling.
- The troposphere's temperature falls with altitude at an average environmental lapse rate of about 6.5°C per km, up to the tropopause.
- The tropopause lies at roughly 8 km altitude over the poles and roughly 18 km over the equator, marking the top of the troposphere.
- The atmosphere is heated predominantly from below: the earth's surface absorbs incoming short-wave solar radiation and re-radiates/transfers heat upward as long-wave radiation, conduction and convection.
- Short-wave solar radiation passes through the lower atmosphere with comparatively little direct absorption by the air itself, unlike long-wave terrestrial radiation which the atmosphere absorbs more readily.
- Above the troposphere, the stratosphere reverses the pattern — its temperature rises with height because ozone there absorbs ultraviolet radiation directly.
b is the mechanism that produces a — air further from the surface gets less of that heat, so it is cooler.
- Assuming the sun heats the air directly and in bulk, rather than heating the surface, which then heats the air from below
- Agreeing both statements in an assertion-explanation pair are true while still picking the option that denies the causal link between them
- Confusing the troposphere's cooling-with-height pattern with the stratosphere's opposite, warming-with-height pattern
MPSC regularly tests atmospheric structure through this exact 'two statements, is the second the explanation of the first' format, most often on the troposphere's lapse rate and its surface-heating mechanism, since the pairing offers a clean cause-and-effect relationship to probe. The same technique is used elsewhere in physical geography — for instance pairing a monsoon-onset fact with its Inter-Tropical Convergence Zone cause, or a tide-height fact with its lunar-gravity cause — so recognising this question style and checking for a genuine causal link, not just the truth of each line, is a transferable exam skill.
No directly related past PYQ was found.
- practice — not a real PYQ
Which of the following correctly explains why the stratosphere's temperature rises with increasing altitude, unlike the troposphere below it ?
- (a)The stratosphere is heated directly by the earth's surface, like the troposphere
- (b)Ozone in the stratosphere absorbs ultraviolet radiation directly, warming the layer from within
- (c)The stratosphere receives no solar radiation at all
- (d)The stratosphere is closer to the sun than the troposphere
Answer(b) Ozone in the stratosphere absorbs ultraviolet radiation directly, warming the layer from within — this is the opposite heating mechanism to the troposphere, which is warmed chiefly by the earth's surface below it rather than by direct radiation absorption at altitude.
- practice — not a real PYQ
The average environmental lapse rate in the troposphere is approximately how much temperature fall per kilometre of altitude gained ?
- (a)1°C
- (b)3.5°C
- (c)6.5°C
- (d)10°C
Answer(c) 6.5°C — this is the standard average environmental lapse rate for the troposphere, though the dry adiabatic lapse rate (about 9.8°C/km) and wet adiabatic lapse rate (varies, typically lower) describe the cooling of a specific rising air parcel rather than the average state of the surrounding atmosphere.