The Poles Are Cold Because of an Angle, Not a Distance
Learn why a spherical Earth is heated unevenly, what happens to sunlight when it is reflected, absorbed and re-radiated, how latitude sets the intensity received, and how the greenhouse effect keeps heat in.
Are the poles cold because they are further from the Sun?
No. The distance makes no meaningful difference at all — the cause is the angle at which sunlight arrives.
The Earth is a sphere, so sunlight cannot strike every part of it squarely. Near the equator the rays fall almost vertically and a beam of given width lands on a small patch of ground. Near the poles the same beam arrives very obliquely and is spread over a much larger patch — so every square metre receives far less.
Try it with a torch. Shine it straight down at a table and you get a small, bright circle. Tilt the torch and the same light spreads into a large, dim ellipse. The torch has not changed what it emits; only the area it is spread over has changed.
The difference in distance from the Sun between the equator and a pole is utterly negligible compared with the Earth-Sun distance. Everything follows from the geometry of a curved surface meeting parallel rays. This page covers the first part of the CBSE Class 9 Science chapter on the Earth as a system.
The Earth is a sphere, so sunlight cannot strike every part of it squarely. Near the equator the rays fall almost vertically and a beam of given width lands on a small patch of ground. Near the poles the same beam arrives very obliquely and is spread over a much larger patch — so every square metre receives far less.
Try it with a torch. Shine it straight down at a table and you get a small, bright circle. Tilt the torch and the same light spreads into a large, dim ellipse. The torch has not changed what it emits; only the area it is spread over has changed.
The difference in distance from the Sun between the equator and a pole is utterly negligible compared with the Earth-Sun distance. Everything follows from the geometry of a curved surface meeting parallel rays. This page covers the first part of the CBSE Class 9 Science chapter on the Earth as a system.
Why does a spherical Earth get heated unevenly?
Because a curved surface presents every possible angle to the incoming rays, and the angle decides how concentrated the energy is.
Sunlight reaching the Earth travels in effectively parallel rays, because the Sun is so far away. A flat screen held square to those rays would be lit evenly all over. A sphere cannot be square to them everywhere at once.
The two consequences of an oblique angle:
- The energy is spread over a larger area. If a beam that covers one square metre where the rays are vertical covers two square metres where they are oblique, then each square metre receives half as much
- The rays pass through more atmosphere. An oblique path is a longer path through the air, so more of the radiation is absorbed and scattered before it reaches the ground at all
Everyday evidence beyond the torch. Notice how much hotter the midday Sun feels than the same Sun at four in the afternoon. Nothing about the Sun changed in those hours; its rays simply became more oblique as it moved down the sky, and the same energy spread over more ground. The daily cycle of heat repeats in miniature what latitude does permanently.
The tilt of the Earth adds the seasons. The Earth's axis is tilted, so as it goes round the Sun, the hemisphere tilted towards the Sun receives more vertical rays and has summer while the other has winter. The mechanism is identical — it is angle again, changing through the year instead of with position.
It is the angle, not the distance, in every one of these cases. The Sun at four o'clock is no further away than at noon. The winter hemisphere is no further from the Sun than the summer one. Once you have the torch picture, every case on this page is the same case — and attributing any of it to distance is the standard error the section exists to correct.
Sunlight reaching the Earth travels in effectively parallel rays, because the Sun is so far away. A flat screen held square to those rays would be lit evenly all over. A sphere cannot be square to them everywhere at once.
The two consequences of an oblique angle:
- The energy is spread over a larger area. If a beam that covers one square metre where the rays are vertical covers two square metres where they are oblique, then each square metre receives half as much
- The rays pass through more atmosphere. An oblique path is a longer path through the air, so more of the radiation is absorbed and scattered before it reaches the ground at all
Everyday evidence beyond the torch. Notice how much hotter the midday Sun feels than the same Sun at four in the afternoon. Nothing about the Sun changed in those hours; its rays simply became more oblique as it moved down the sky, and the same energy spread over more ground. The daily cycle of heat repeats in miniature what latitude does permanently.
The tilt of the Earth adds the seasons. The Earth's axis is tilted, so as it goes round the Sun, the hemisphere tilted towards the Sun receives more vertical rays and has summer while the other has winter. The mechanism is identical — it is angle again, changing through the year instead of with position.
It is the angle, not the distance, in every one of these cases. The Sun at four o'clock is no further away than at noon. The winter hemisphere is no further from the Sun than the summer one. Once you have the torch picture, every case on this page is the same case — and attributing any of it to distance is the standard error the section exists to correct.
What happens to sunlight when it reaches the Earth?
It is reflected, absorbed, or absorbed and then re-radiated at a longer wavelength — and only the absorbed part warms anything.
The three fates of incoming solar radiation:
- Part is reflected straight back to space — by clouds, by the atmosphere itself, and by bright surfaces such as snow, ice, pale sand and water struck at a low angle
- Part is absorbed by the atmosphere — by water vapour, dust and gases on the way down
- Part is absorbed by the Earth's surface, which warms as a result
Then the surface re-radiates. A warmed surface does not keep the energy; it radiates it back outwards. But it radiates at a much longer wavelength than the sunlight that arrived — as infrared or heat radiation, rather than as visible light.
That change of wavelength is the crucial step, because the atmosphere treats short and long wavelengths quite differently — which is what the last section of this page depends on.
Reflectivity differs enormously between surfaces. Fresh snow reflects most of the light falling on it and warms very little. A dark forest, ploughed soil or a tarred road reflects very little and absorbs a great deal.
Everyday evidence. A whitewashed terrace or a light-coloured roof stays noticeably cooler than a dark one through a summer afternoon, and people wear light clothes in hot weather for the same reason. Walk barefoot across a tarred road and then across white marble at the same hour and the difference is unmistakable — same Sun, same angle, different absorption.
Only the absorbed fraction warms a surface. Reflected radiation bounces away and heats nothing. That is why the colour of a surface matters so much, and it explains something important about a warming world: as ice and snow melt, the bright reflecting surface is replaced by dark land or water that absorbs instead, so the warming accelerates itself.
So the Earth's temperature is a balance, not a total. Energy arrives from the Sun and energy leaves as infrared, and the surface settles at whatever temperature makes the two equal. Anything that changes either side of that balance — the reflectivity of the surface, or how easily the infrared escapes — changes the temperature.
The three fates of incoming solar radiation:
- Part is reflected straight back to space — by clouds, by the atmosphere itself, and by bright surfaces such as snow, ice, pale sand and water struck at a low angle
- Part is absorbed by the atmosphere — by water vapour, dust and gases on the way down
- Part is absorbed by the Earth's surface, which warms as a result
Then the surface re-radiates. A warmed surface does not keep the energy; it radiates it back outwards. But it radiates at a much longer wavelength than the sunlight that arrived — as infrared or heat radiation, rather than as visible light.
That change of wavelength is the crucial step, because the atmosphere treats short and long wavelengths quite differently — which is what the last section of this page depends on.
Reflectivity differs enormously between surfaces. Fresh snow reflects most of the light falling on it and warms very little. A dark forest, ploughed soil or a tarred road reflects very little and absorbs a great deal.
Everyday evidence. A whitewashed terrace or a light-coloured roof stays noticeably cooler than a dark one through a summer afternoon, and people wear light clothes in hot weather for the same reason. Walk barefoot across a tarred road and then across white marble at the same hour and the difference is unmistakable — same Sun, same angle, different absorption.
Only the absorbed fraction warms a surface. Reflected radiation bounces away and heats nothing. That is why the colour of a surface matters so much, and it explains something important about a warming world: as ice and snow melt, the bright reflecting surface is replaced by dark land or water that absorbs instead, so the warming accelerates itself.
So the Earth's temperature is a balance, not a total. Energy arrives from the Sun and energy leaves as infrared, and the surface settles at whatever temperature makes the two equal. Anything that changes either side of that balance — the reflectivity of the surface, or how easily the infrared escapes — changes the temperature.
How does latitude decide the temperature of a place?
The higher the latitude, the more obliquely the rays arrive, so the less energy each square metre receives.
Latitude is the angular distance north or south of the equator — at the equator, rising to at each pole.
As latitude increases, the angle of the incoming rays becomes more oblique, so the intensity of radiation per unit area falls. The result is hottest near the equator, coldest at the poles, and moderate in between.
The three heat zones:
- Torrid or tropical zone — between the Tropic of Cancer and the Tropic of Capricorn. The Sun is overhead at some time of the year, so the rays are at their most vertical and this is the hottest zone
- Temperate zones — between each tropic and the corresponding polar circle. The Sun is never overhead, so the rays are always somewhat oblique, and temperatures are moderate
- Frigid or polar zones — beyond the polar circles. The rays are very oblique all year, and there are long periods of continuous daylight and continuous darkness
Worked comparison. If a beam that illuminates at the equator is spread over at a higher latitude, then each square metre there receives of the energy. Spread over and it receives . The intensity falls in exact proportion to the area the beam covers, which is the torch calculation made numerical.
Everyday evidence within one country. The far south of India is warm throughout the year while the high Himalaya lie under snow. Part of that is latitude and part is altitude, and neither place is further from the Sun in any way that matters.
Latitude is not the only control on temperature. Three others matter as much in particular places:
- Altitude — higher places are colder, which is why a hill station is cool although it may share a latitude with a hot plain
- Distance from the sea — coastal places have a smaller range between day and night and between seasons, while inland places swing much further
- Ocean currents and winds, which carry heat from where it was received to where it was not
So two places at the same latitude can have quite different climates, and that is why latitude gives the broad pattern and not the local answer. The winds and currents that redistribute the heat are the subject of the next part of this chapter.
Latitude is the angular distance north or south of the equator — at the equator, rising to at each pole.
As latitude increases, the angle of the incoming rays becomes more oblique, so the intensity of radiation per unit area falls. The result is hottest near the equator, coldest at the poles, and moderate in between.
The three heat zones:
- Torrid or tropical zone — between the Tropic of Cancer and the Tropic of Capricorn. The Sun is overhead at some time of the year, so the rays are at their most vertical and this is the hottest zone
- Temperate zones — between each tropic and the corresponding polar circle. The Sun is never overhead, so the rays are always somewhat oblique, and temperatures are moderate
- Frigid or polar zones — beyond the polar circles. The rays are very oblique all year, and there are long periods of continuous daylight and continuous darkness
Worked comparison. If a beam that illuminates at the equator is spread over at a higher latitude, then each square metre there receives of the energy. Spread over and it receives . The intensity falls in exact proportion to the area the beam covers, which is the torch calculation made numerical.
Everyday evidence within one country. The far south of India is warm throughout the year while the high Himalaya lie under snow. Part of that is latitude and part is altitude, and neither place is further from the Sun in any way that matters.
Latitude is not the only control on temperature. Three others matter as much in particular places:
- Altitude — higher places are colder, which is why a hill station is cool although it may share a latitude with a hot plain
- Distance from the sea — coastal places have a smaller range between day and night and between seasons, while inland places swing much further
- Ocean currents and winds, which carry heat from where it was received to where it was not
So two places at the same latitude can have quite different climates, and that is why latitude gives the broad pattern and not the local answer. The winds and currents that redistribute the heat are the subject of the next part of this chapter.
How does the greenhouse effect keep heat near the surface?
Sunlight comes in easily as short wavelengths and heat struggles to get out as long ones, because certain atmospheric gases absorb the long wavelengths and send some of the energy back down.
The greenhouse effect, step by step:
- Short-wavelength sunlight passes readily through the atmosphere and reaches the surface
- The surface absorbs it and warms
- The warmed surface re-radiates energy as long-wavelength infrared
- Certain gases in the atmosphere absorb that infrared radiation and re-emit it in all directions, including back down towards the surface
- So heat is retained near the surface, keeping the Earth far warmer than it would otherwise be
The greenhouse gases: carbon dioxide, methane, water vapour, nitrous oxide and ozone.
Everyday evidence. A car parked in the sun with its windows closed becomes far hotter inside than the air outside. Sunlight passes through the glass, is absorbed by the seats and dashboard, and the re-radiated heat cannot escape through the glass as easily as the light entered. A glass greenhouse for plants works the same way, which is where the effect gets its name.
The natural greenhouse effect is essential. Without it, the Earth's surface would be far too cold for life as we know it, and its temperature would swing violently between day and night. The atmosphere is what keeps the planet habitable, and the effect has been operating for as long as the atmosphere has existed.
The problem is the enhancement of it, not the effect itself. Burning coal, petroleum and natural gas releases carbon dioxide that had been locked away for very long periods, and clearing forests removes the photosynthesis that would take some of it back. The concentration of greenhouse gases rises, more infrared is trapped, and the surface warms further.
**So greenhouse effect is not a synonym for pollution. It is a natural and necessary process being intensified by human activity, and the distinction matters because a question asking what the greenhouse effect does wants the natural mechanism, while a question about global warming wants the enhancement.
This closes the chain begun at the start of the page. Uneven heating by angle decides where energy arrives. Reflection and absorption decide how much stays. And the greenhouse effect decides how long** it stays before leaving as infrared. Together those three settle the Earth's temperature — and the winds and currents of the next part of this chapter decide how it is shared out.
The greenhouse effect, step by step:
- Short-wavelength sunlight passes readily through the atmosphere and reaches the surface
- The surface absorbs it and warms
- The warmed surface re-radiates energy as long-wavelength infrared
- Certain gases in the atmosphere absorb that infrared radiation and re-emit it in all directions, including back down towards the surface
- So heat is retained near the surface, keeping the Earth far warmer than it would otherwise be
The greenhouse gases: carbon dioxide, methane, water vapour, nitrous oxide and ozone.
Everyday evidence. A car parked in the sun with its windows closed becomes far hotter inside than the air outside. Sunlight passes through the glass, is absorbed by the seats and dashboard, and the re-radiated heat cannot escape through the glass as easily as the light entered. A glass greenhouse for plants works the same way, which is where the effect gets its name.
The natural greenhouse effect is essential. Without it, the Earth's surface would be far too cold for life as we know it, and its temperature would swing violently between day and night. The atmosphere is what keeps the planet habitable, and the effect has been operating for as long as the atmosphere has existed.
The problem is the enhancement of it, not the effect itself. Burning coal, petroleum and natural gas releases carbon dioxide that had been locked away for very long periods, and clearing forests removes the photosynthesis that would take some of it back. The concentration of greenhouse gases rises, more infrared is trapped, and the surface warms further.
**So greenhouse effect is not a synonym for pollution. It is a natural and necessary process being intensified by human activity, and the distinction matters because a question asking what the greenhouse effect does wants the natural mechanism, while a question about global warming wants the enhancement.
This closes the chain begun at the start of the page. Uneven heating by angle decides where energy arrives. Reflection and absorption decide how much stays. And the greenhouse effect decides how long** it stays before leaving as infrared. Together those three settle the Earth's temperature — and the winds and currents of the next part of this chapter decide how it is shared out.
Exam tip
Exam tip: say angle, never distance
The poles are colder because of the angle of the rays, not the distance from the Sun. State the angle explicitly — it is the whole answer.
Give both consequences of an oblique angle: the energy is spread over a larger area, and the rays pass through more atmosphere.
Use the torch comparison if a diagram is wanted — a small bright circle when square on, a large dim ellipse when tilted.
Name the three fates of incoming radiation: reflected, absorbed by the atmosphere, absorbed by the surface — and say that only the absorbed part warms anything.
Say that the surface re-radiates at a longer wavelength, as infrared. That change of wavelength is what the greenhouse effect depends on.
Note that bright surfaces reflect and dark surfaces absorb, and that melting ice accelerates warming by replacing a reflector with an absorber.
Name the three heat zones with their boundaries: torrid between the tropics, temperate between tropic and polar circle, frigid beyond the polar circles.
Name the other controls on temperature besides latitude: altitude, distance from the sea, and winds and currents.
Give the greenhouse effect as five steps, name the gases, and state that the natural effect is essential while its enhancement is the problem.
And use the closed car or glass greenhouse as the everyday illustration.
Give both consequences of an oblique angle: the energy is spread over a larger area, and the rays pass through more atmosphere.
Use the torch comparison if a diagram is wanted — a small bright circle when square on, a large dim ellipse when tilted.
Name the three fates of incoming radiation: reflected, absorbed by the atmosphere, absorbed by the surface — and say that only the absorbed part warms anything.
Say that the surface re-radiates at a longer wavelength, as infrared. That change of wavelength is what the greenhouse effect depends on.
Note that bright surfaces reflect and dark surfaces absorb, and that melting ice accelerates warming by replacing a reflector with an absorber.
Name the three heat zones with their boundaries: torrid between the tropics, temperate between tropic and polar circle, frigid beyond the polar circles.
Name the other controls on temperature besides latitude: altitude, distance from the sea, and winds and currents.
Give the greenhouse effect as five steps, name the gases, and state that the natural effect is essential while its enhancement is the problem.
And use the closed car or glass greenhouse as the everyday illustration.
Did you know
Why melting ice makes the melting faster
Of everything on the Earth's surface, fresh snow and ice are the best reflectors. They send most of the sunlight falling on them straight back out, absorb very little, and stay cold as a result.
Which means a snow-covered surface is, in a sense, protecting itself. The reflection keeps it cool, and staying cool keeps it snow-covered.
Now warm things up enough that some of the ice melts. What is left behind is dark ocean water or bare rock and soil — and those are among the poorest reflectors and the best absorbers. Where the surface reflected most of the incoming light, it now absorbs most of it.
So the newly exposed surface warms more, which melts more ice nearby, which exposes more dark surface, which absorbs still more. The process reinforces itself, and each step makes the next step easier.
That kind of self-reinforcing chain is why a small initial warming in the polar regions can produce a much larger change there than elsewhere. The reflectivity of the surface is not a fixed property of the planet; it is something the temperature itself alters.
The same reasoning works in reverse, and reassuringly so. A cooling that allows snow to lie a little longer each year increases the reflection, which encourages further cooling. The mechanism has no preferred direction — it simply amplifies whatever change begins.
And it is worth noticing that nothing in this involves the greenhouse effect at all. This is reflection and absorption, the middle section of this page, acting on its own. The Earth's temperature is settled by several mechanisms at once, and knowing which one a question is asking about is half the answer.
Which means a snow-covered surface is, in a sense, protecting itself. The reflection keeps it cool, and staying cool keeps it snow-covered.
Now warm things up enough that some of the ice melts. What is left behind is dark ocean water or bare rock and soil — and those are among the poorest reflectors and the best absorbers. Where the surface reflected most of the incoming light, it now absorbs most of it.
So the newly exposed surface warms more, which melts more ice nearby, which exposes more dark surface, which absorbs still more. The process reinforces itself, and each step makes the next step easier.
That kind of self-reinforcing chain is why a small initial warming in the polar regions can produce a much larger change there than elsewhere. The reflectivity of the surface is not a fixed property of the planet; it is something the temperature itself alters.
The same reasoning works in reverse, and reassuringly so. A cooling that allows snow to lie a little longer each year increases the reflection, which encourages further cooling. The mechanism has no preferred direction — it simply amplifies whatever change begins.
And it is worth noticing that nothing in this involves the greenhouse effect at all. This is reflection and absorption, the middle section of this page, acting on its own. The Earth's temperature is settled by several mechanisms at once, and knowing which one a question is asking about is half the answer.
Exam relevance
How does the energy balance of the Earth feed into JEE and NEET?
This page sits at the meeting point of physics, chemistry and environmental science, and each of those routes picks it up differently.
The physics of radiation is the foundation for Class 11 Physics Thermal Properties of Matter, examined in JEE Main and in NEET Physics. That chapter treats radiation as the third mode of heat transfer alongside conduction and convection, and introduces the idea that a hotter body radiates at shorter wavelengths while a cooler one radiates at longer wavelengths. The Class 9 statement that the Sun sends short-wavelength light and the Earth re-radiates long-wavelength infrared is that principle applied, and it is the reason the greenhouse effect works at all.
A black body, a perfect absorber and radiator, is introduced there too — and the Class 9 observation that dark surfaces absorb and bright surfaces reflect is its qualitative form.
The chemistry connects to Class 11 Environmental Chemistry and to Class 12 discussions of atmospheric pollution, where greenhouse gases are named and their sources identified. Carbon dioxide, methane and the effect of fossil fuel combustion are examined there, and it is common ground for JEE Main and NEET Chemistry.
The biology connects to Class 12 Ecosystem and Environmental Issues, examined in NEET, where global warming, the enhanced greenhouse effect and their consequences for ecosystems are treated. The Class 9 distinction between the natural effect and its enhancement is exactly the distinction that chapter requires.
Latitude and solar intensity also underlie the discussion of biomes and productivity in Class 12 ecology — the tropics being the most productive regions follows directly from receiving the most intense radiation.
What the questions look like. For NEET, assertion-reason items are the commonest form on this material, and favourites are that the poles are colder because of the angle rather than the distance, and that the natural greenhouse effect is necessary for life. Match-the-column questions pair a gas with its status as a greenhouse gas, or a zone with its latitude limits. For JEE Main, the radiation physics appears as numericals on Stefan's law and Wien's law in Class 11, where this page's qualitative statements become formulas.
How board and competitive emphasis differ. A board paper asks you to explain why the equator is hotter than the poles and to describe the greenhouse effect in steps, marking for completeness. A competitive paper asks which statement about radiation is correct, or sets a numerical on wavelength and temperature — so the mechanism matters more than the description, and the wavelength point becomes essential rather than incidental.
The single trap that costs the most marks. Explaining polar cold by distance from the Sun. The difference in distance is negligible; the cause is entirely the angle and therefore the area over which the energy is spread. This is asked directly and it is asked as an assertion-reason pair, and an answer mentioning distance is marked wrong however well the rest is written.
A second trap worth naming. Treating the greenhouse effect as a form of pollution. It is a natural process without which the Earth would be uninhabitable; what human activity has done is intensify it. A question asking about the greenhouse effect wants the mechanism, and one asking about global warming wants the enhancement — and using one answer for the other loses the mark.
The physics of radiation is the foundation for Class 11 Physics Thermal Properties of Matter, examined in JEE Main and in NEET Physics. That chapter treats radiation as the third mode of heat transfer alongside conduction and convection, and introduces the idea that a hotter body radiates at shorter wavelengths while a cooler one radiates at longer wavelengths. The Class 9 statement that the Sun sends short-wavelength light and the Earth re-radiates long-wavelength infrared is that principle applied, and it is the reason the greenhouse effect works at all.
A black body, a perfect absorber and radiator, is introduced there too — and the Class 9 observation that dark surfaces absorb and bright surfaces reflect is its qualitative form.
The chemistry connects to Class 11 Environmental Chemistry and to Class 12 discussions of atmospheric pollution, where greenhouse gases are named and their sources identified. Carbon dioxide, methane and the effect of fossil fuel combustion are examined there, and it is common ground for JEE Main and NEET Chemistry.
The biology connects to Class 12 Ecosystem and Environmental Issues, examined in NEET, where global warming, the enhanced greenhouse effect and their consequences for ecosystems are treated. The Class 9 distinction between the natural effect and its enhancement is exactly the distinction that chapter requires.
Latitude and solar intensity also underlie the discussion of biomes and productivity in Class 12 ecology — the tropics being the most productive regions follows directly from receiving the most intense radiation.
What the questions look like. For NEET, assertion-reason items are the commonest form on this material, and favourites are that the poles are colder because of the angle rather than the distance, and that the natural greenhouse effect is necessary for life. Match-the-column questions pair a gas with its status as a greenhouse gas, or a zone with its latitude limits. For JEE Main, the radiation physics appears as numericals on Stefan's law and Wien's law in Class 11, where this page's qualitative statements become formulas.
How board and competitive emphasis differ. A board paper asks you to explain why the equator is hotter than the poles and to describe the greenhouse effect in steps, marking for completeness. A competitive paper asks which statement about radiation is correct, or sets a numerical on wavelength and temperature — so the mechanism matters more than the description, and the wavelength point becomes essential rather than incidental.
The single trap that costs the most marks. Explaining polar cold by distance from the Sun. The difference in distance is negligible; the cause is entirely the angle and therefore the area over which the energy is spread. This is asked directly and it is asked as an assertion-reason pair, and an answer mentioning distance is marked wrong however well the rest is written.
A second trap worth naming. Treating the greenhouse effect as a form of pollution. It is a natural process without which the Earth would be uninhabitable; what human activity has done is intensify it. A question asking about the greenhouse effect wants the mechanism, and one asking about global warming wants the enhancement — and using one answer for the other loses the mark.
Key takeaways
Uneven heating, radiation and the greenhouse effect: quick revision
- The Earth is heated unevenly because it is a sphere meeting parallel rays, so the angle of arrival differs — not because of any difference in distance from the Sun.
- Near the equator rays fall almost vertically and land on a small area; near the poles they fall obliquely and spread over a large one.
- An oblique angle also means a longer path through the atmosphere, so more is absorbed and scattered on the way down.
- The torch comparison: square on gives a small bright circle, tilted gives a large dim ellipse.
- The daily cycle (noon against late afternoon) and the seasons (from the Earth's tilt) are the same angle effect, changing with time instead of place.
- Three fates of incoming radiation: reflected (clouds, atmosphere, snow, ice, pale sand), absorbed by the atmosphere, and absorbed by the surface.
- The warmed surface re-radiates at a longer wavelength, as infrared — and that change of wavelength is what makes the greenhouse effect possible.
- Only the absorbed fraction warms anything; bright surfaces reflect and dark ones absorb.
- Melting ice accelerates warming, replacing a good reflector with a good absorber.
- The Earth's temperature is a balance between energy arriving and energy leaving as infrared.
- Latitude is the angular distance from the equator, to . Higher latitude means more oblique rays and lower intensity.
- Heat zones: torrid between the tropics (Sun overhead at some time), temperate between tropic and polar circle (never overhead), frigid beyond the polar circles.
- If a beam covering spreads over , each square metre gets the energy.
- Other controls on temperature: altitude, distance from the sea, and winds and ocean currents.
- Greenhouse effect in five steps: short-wavelength sunlight passes in, the surface absorbs and warms, it re-radiates as infrared, greenhouse gases absorb that infrared, and re-emit some of it back down.
- Greenhouse gases: carbon dioxide, methane, water vapour, nitrous oxide, ozone. A closed car in the sun is the everyday illustration.
- The natural effect is essential; the enhancement by burning fossil fuels and clearing forests is the problem.
Explain to somebody why noon is hotter than four o'clock without using the word distance — if the explanation works, the whole of this page has landed.
- Near the equator rays fall almost vertically and land on a small area; near the poles they fall obliquely and spread over a large one.
- An oblique angle also means a longer path through the atmosphere, so more is absorbed and scattered on the way down.
- The torch comparison: square on gives a small bright circle, tilted gives a large dim ellipse.
- The daily cycle (noon against late afternoon) and the seasons (from the Earth's tilt) are the same angle effect, changing with time instead of place.
- Three fates of incoming radiation: reflected (clouds, atmosphere, snow, ice, pale sand), absorbed by the atmosphere, and absorbed by the surface.
- The warmed surface re-radiates at a longer wavelength, as infrared — and that change of wavelength is what makes the greenhouse effect possible.
- Only the absorbed fraction warms anything; bright surfaces reflect and dark ones absorb.
- Melting ice accelerates warming, replacing a good reflector with a good absorber.
- The Earth's temperature is a balance between energy arriving and energy leaving as infrared.
- Latitude is the angular distance from the equator, to . Higher latitude means more oblique rays and lower intensity.
- Heat zones: torrid between the tropics (Sun overhead at some time), temperate between tropic and polar circle (never overhead), frigid beyond the polar circles.
- If a beam covering spreads over , each square metre gets the energy.
- Other controls on temperature: altitude, distance from the sea, and winds and ocean currents.
- Greenhouse effect in five steps: short-wavelength sunlight passes in, the surface absorbs and warms, it re-radiates as infrared, greenhouse gases absorb that infrared, and re-emit some of it back down.
- Greenhouse gases: carbon dioxide, methane, water vapour, nitrous oxide, ozone. A closed car in the sun is the everyday illustration.
- The natural effect is essential; the enhancement by burning fossil fuels and clearing forests is the problem.
Explain to somebody why noon is hotter than four o'clock without using the word distance — if the explanation works, the whole of this page has landed.