What’s preventing temperature across the globe to reach an equilibrium since air flows freely?



If I open the windows in my room, which has AC turned on and it’s cool in the summer, it will quickly become as hot as it is outside, why isn’t it happening around the globe?

In: Physics

Areas around the equator receive very strong sunlight and the poles get very diffuse sunlight, so they do receive different amounts of energy.

The heat energy also doesn’t all stay in the earth and its atmosphere, some is lost into space, so it’s not a closed system.

Because the energy the earth recieves changes all the time. If the sun is hitting about half of the earth all the time, it’s actively warming that part up while the other half is cooling down, throw in wind, geothermal energy, tidal winds, different altitudes. You get quite a volatile heat distribution that can change rapidly

Uneven heating. Heat is added in the day side and lost on the night side much, much faster than the temperature can be equalised through air flow.

We perceive air as this uniform gas that’s just everywhere, when in reality air actually clumps around itself and forms bubbles and pockets. These bubbles form when air of the same temperature and density clump together. You’ll get bubbles of cold air, bubbles of hot air, bubbles of wet air, bubbles of dry air, etc.

In fact, wind is when these bubbles push against each other. The bubbles are so huge and so sharply determined by their heat and density and humidity, that they don’t just blend into each other: they actually form a wall, or a front, and push against each other.

You may have heard the weather forecast talking about a warm front or a cold front coming in. That’s a big bubble of one type of air pushing another. You get wind at the line where the bubbles meet, and one bubble is pushing the other.

Some airline turbulence is also caused by these bubbles, since they don’t just push around horizontally on the surface of the earth but they stack vertically on top of each other into the stratosphere, too. So sometimes when there’s turbulence or the feeling of a sudden drop while flying, it might be because the plane is punching through one air bubble into the next.

The globe is huge and the Earth is continually being heated unevenly, the temperature range on Earth is relatively small.

Because some parts of the planet have a lot more energy flowing into them. If you have a heater running in the corner of your room, the air right in front of it will be warmer, even if you have the window open.

Now imagine your heater was thousands of miles from the window.

If I understand it rightly, it’s always trying for an equilibrium, and always failing. Heat flows from the tropics to the poles, which is why the arctic is warming at the fastest rate on the planet. BUT – air has very little heat capacity, and air temperature is very much conditioned by the local ground or sea surface temperature. Most of the heat that reaches the planet ends up in the oceans, and it takes a very long time for heat to distribute through the water column. So ocean currents transport heat around, and where they go is shaped by continents. The Arctic, for instance, is much more open to heat inflow than the Antarctic, which is walled off to some degree by the winds and currents circling it (not entirely – as the oceans warm they eat away at Antarctic ice sheets).

Because our planet is so big that temperature(mostly through convection) can never move fast enough to overcome the uneven heating it receives from the sun.

It does, all the time. The poles would be way colder and the equators so hot as to be uninhabitable otherwise. The air inside your house in your example is like the air between the poles and the equator, rushing from the cold place (the poles) to the hot place (the equator) and unlike you example, the air then rushes back again. So you have the cold air falling down and moving to the equator and the warm air rising up and moving back to the poles. Even in your example, more cold air is made at your AC and if you stand right next to it, you will still have cold air no matter if the windows are open. That’s the poles. The cold spot.

You example does work very well because the AC is weak and tiny compared to the might of the sun, so there is no balance. In the earth, though, the net heat loss at the pole is equal to the net heat gain at the equator, which is why the heat doesn’t overwhelm the cold.

Because air does not move as fast as the Earth rotates.

Consider a stupidly simple setup –
If air to be moving at 500 km/h (imagine the wind), it would take about 3 days for it to go around the Earth. In those 3 days, the Earth has rotated thrice…so the heating from the Sun has changed it direction three times. So before the air temperature cam equalize the heating has shifted to another side.

Its like you keep moving your heater or AC to different parts of the room before the air can actually circulate and reach a constant temperature all over.

Of course, air doesnt move at 500 km/h , and a lot more complicated stuff happens – land heats up faster than the sea, the earth is tilted depending on season etc. All this makes it even mlre impossible to reach a constant temperature .

ELI15: This is why whether is a ‘dynamic/chaotic’ system. Energy us being fed to the system ‘anisotropically’ faster than the system can ‘equilibrate or reach a steady state’.

Your room is a small. Maybe 10 metres across. Even air moving at 10 metres/h (your walking speed is about 5000 m/h) would completely exchange with the outside within an hour. But even it doesnt really have a constant temperature if AC / heater is on. The air close to the device is hotter/ cooler. It just moves around quickly enough for you to not notice the tiny difference in temperature if you open the room.

Given your example, turn on the air on one room and open all doors to the other rooms, not to the outside. The room with the AC will be cooler, right? Because while the gas which carries heat diffuses it’s not really a closed system and it’s still exchaging heat with the outside. It’s not a thermodynamically closed system.

Well Earth is the same just in a much bigger scale. Different parts recieve different amounts of heat and while it travels. Wind is caused because of the different densities / temperatures (both are related). Earth still loses heat. Also given the Albedo effect, where there is Ice like the poles, more light/heat is reflected back into space.

The very short answer is because Earth is not a static system. Between it’s orbit (closer and further from the sun in an ellipse), rotation and tilt (daily cyclic energy input as well as the Coriolis effect of the planet dragging the air along with it ), and even the moon’s tug there are plenty of forces constantly acting to slosh things around. More importantly, the sun is adding an enormous amount of energy to the system…but only on half the globe at once. This daily heating and cooling – thus cyclic expansion, contraction, and thermal updrafts cause most of what we consider weather and climate. Even if there was no sun suddenly, there isn’t enough time in half a day to get the world’s temperature differentials to settle out and become homogeneous.

Adding to the other explanations here: The Sunshine slants down at different angles as you go towards or away from the Equator.

So, in addition to “it’s day here/night there, and the atmosphere is mostly rotating about as fast as the surface is”, add “the Sun is shining straight down _here_ (this is always somewhere within 23 degrees of the equator, and right on it at spring/fall equinox) and shining very slanted at the Poles – never more than 23 degrees high in the sky, and half the year not at all”.

So sunshine heats the Earth up pretty unevenly, which gets transferred to the local atmosphere to affect its temperature.

Plus which, conduction (heat transfer between things touching, like pieces of atmosphere, or Earth’s surface and atmosphere touching it) and convection (heat being carried by the air or water as it moves) are local, not global, and take time to spread heat from one locale to another. Jet steams can make convection go faster, but never instantly.

–Dave, soooomewhere, oooover the raaaainbow

Imagine you have a heater in one side of your house and a cooling machine on the other side. You won’t reach an equilibrium. It’ll be hot on one side and cold on the other and warm in the middle.

The earth has a tilt causing half to recieve more sun therefore heating it, making it summer, and the other half to be colder making it winter. U

It does always try to reach equilibrium. Water is one of the major variable regulators. The hotter the world gets, the more hurricanes we get, because they are the end results of dissipating heat.

We are getting hotter because of deforestation for monoculture agriculture. I can elaborate a lot more on this if requested.

The sun is constantly changing position relative to the Earth and heating up different areas. Air also does not mix very well compared to liquids, so you get warm air constantly rising and cooler air taking it’s place, only to be warmed up by the ground and cycle up. Basically, conditions are changing faster than the air has a chance to mix.