If heat rises, why does it get colder as you climb up mountains?

– Ollie, 8, Christchurch, New Zealand

That is an excellent and thoughtful question Ollie – why indeed?

You’re right, when air is warmed, it rises. This is what gives us the “thermals” gliders can use to soar upwards and large birds of prey like the South American condors use to help them stay aloft for hours at a time.

But there are lots of other things influencing air temperature. When air rises, it expands because air pressure decreases with height. The energy in the air gets spread out over greater volumes and its temperature goes down.

This effect wins out over warm air rising. The warm air in a thermal will cool as it rises, until it reaches the temperature of the air around it and is no longer buoyant.

But why do we have rising air at all?

That’s because the air around us is heated from below, from Earth’s surface.

When the Sun is shining, it doesn’t heat the air in the lowest few kilometres of the atmosphere (the troposphere) as there are very few gases in that air to absorb sunlight.

The Sun’s rays heat Earth, not the air. The air is then warmed from below, from the ground, just as water in a pot on a stove is warmed from the bottom of the pot.

Earth’s greenhouse

Earth mostly sends energy back to space in the form of heat or infrared radiation (with wavelengths longer than visible light but shorter than microwaves), and there are plenty of gases in the air that are good at absorbing this kind of radiation, even if they don’t feel the sun’s energy.

These are what we call greenhouse gases – water vapour, carbon dioxide, methane and so on. Because we have these in the air, the absorption of infrared energy is the main way the air is warmed.

Again, air near the ground is warmed the most by this absorption of energy. The warm air near Earth is buoyant so it often “bubbles up” into the atmosphere, just like the water in a pot on a stove.

But in the atmosphere, the decrease of pressure with height dictates that temperatures decrease as you go up. This is what’s known in weather jargon as the “lapse rate” – how fast temperatures decrease with height. In dry air (no water vapour), that rate is just under 10°C per kilometre, or a little under 1°C cooler per 100 metres upwards.

When we have water vapour in the air, it’s a different story. As the air rises and cools, it can’t hold so much water vapour, so some of the vapour has to condense back into liquid water. As it does that, it releases the energy it took to evaporate it in the first place.

That heat warms the air and reduces the “lapse rate”. How big this effect is depends on how much moisture was in the air to start with. On average, the temperature decrease of about 10°C per kilometre goes down to around 6.5°C per kilometre.

And what happens to that liquid water in the air? If forms tiny droplets that make clouds. If enough of those drops stick together and become heavy enough, they’ll fall back to Earth as rain.

Clouds, rain and lightning

We have clouds and rain because temperatures decrease with height. The clouds that form this way, through buoyant air rising in thermals, are known as cumulus clouds.

Cumulus always have lumpy tops, looking a bit like a cauliflower. That’s because different parts of the rising air have different amounts out water vapour in them. So different amounts of energy are released, giving the air different buoyancy in different places. The moistest, most buoyant air rises the highest, while drier less buoyant air doesn’t make it so far up.

If there is lots of moisture available, we can get a thunderstorm cloud, with thunder and lightning as well as plenty of rain. Not just rain either, but often hail (frozen rain).

That happens because the temperature in the upper parts of such deep clouds is well below freezing, so it is made up of ice crystals rather than water drops. Those ice crystals can stick together to form hail, or snow.

Curiously, it’s the collisions between ice crystals and water drops as they go up and down in a deep cumulus cloud that gives rise to lightning, with a build-up of positive electrical charges at the top of the cloud and negative charges at the bottom.

Getting back to your original question, why is it colder in the mountains? That’s because as we climb a mountain, we are moving into cooler layers of the atmosphere. We are getting above the surface layers of the atmosphere, going to lower pressures, and that causes the temperature to drop.

Warm air can still rise from a mountaintop, but it’ll be cooler to start with than air down at sea level, just because it’s at a lower pressure. Climbers who tackle really high mountains, like Mount Everest, usually take oxygen cylinders with them as the air is so thin near the top of such high peaks.

That’s also why snow and ice linger on mountain tops, as that’s where it is cold enough year-round to keep the ice frozen.

Hello curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to curiouskids@theconversation.edu.au. Please tell us your name, age and the city where you live.

James Renwick, Professor, Physical Geography (Climate Science), Te Herenga Waka — Victoria University of Wellington

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If you scoop a bucket of water out of the ocean, does it get lower?

–Ellis, 6 and a half, Hobart

This is a great question Ellis! The short answer is yes, but the change in water level will be extremely tiny. You can actually test this idea at home.

For starters, you’ll need a glass of water and a teaspoon. Fill the glass almost to the top, and take note of the water level. Now, carefully remove a teaspoon of water. Can you see the difference in the water level? Maybe you can, but maybe not.

You could repeat this experiment in the kitchen sink, or a bathtub if you have one. The key point is that the water level does drop, but only by a very small amount. If you scoop a teaspoon of water out of the bathtub, you probably won’t see the difference with the naked eye.

Millions of buckets

So, let’s return to the ocean. It’s truly huge, especially compared to a bucket.

Let’s say that you have a bucket that fits ten litres. Using the information here, there are about 137 million, million, million buckets of water in the ocean (that is, all of Earth’s oceans combined).

I crunched the numbers. If you took a bucket of water from the ocean, the water level would drop by around 0.0000000000277 millimetre. You can see how small a millimetre is on your school ruler. We don’t have anything on Earth that can measure anything this small. For example, this is way, way, way smaller than even a single atom.

So, the more detailed answer to your question is: yes, the water level gets lower, but by such a small amount that we can’t even measure it.

But wait, there’s more

Earth is a really interesting place. When you take your bucket of water, all that water is moving through something called the water cycle.

Sea levels are actually constantly changing. Each year, a lot of water evaporates from the ocean. Some of it is even lost to outer space.

However, most of the evaporated water rains back down directly onto the ocean, or onto the ground, with that water making its way to rivers that eventually flow to the ocean. There is also a lot of water stored underground, and some of it makes its way to the ocean, as well.

So, if you poured your bucket of water onto the ground, eventually it would end up back in the ocean via the water cycle!

A few fun facts

There’s a lot to know about water. Some more fun facts (and big numbers):

1. There are 1,500,000,000,000,000,000 molecules of water (H₂O) in a single drop of water. That’s 1.5 million, million, million.

2. The oldest water in the world is estimated to have fallen as rain more than 1.6 billion years ago.

3. Most (about 98%) of the world’s fresh, liquid water is underground – that’s why it’s called groundwater.

Dylan Irvine, Outstanding Future Researcher - Northern Water Futures, Charles Darwin University

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Do whales fart and sneeze? — Guy, age 8, Sydney

I’ve waited a long time for a question like this! I usually talk about whale snot for my research (yes, whales have snot), and I’m so excited to look into this, too.

Let’s start with the tail end first: farts

Yes, whales do fart. Can you imagine the size and bubbles of a fart from the world’s biggest animal, the blue whale?

I’m yet to experience this, but I know of some lucky scientists who have seen a humpback whale fart. They tell me it looks like bubbles coming out underneath its body near the tail. That’s where the whale bum is — the smellier blowhole.

Whales are mammals, just like us. This means they breathe air, give birth to live young, provide their young with milk and have hair, usually in the form of whiskers around their mouth. They also have digestive processes to help break down their food.

Unlike us, whales don’t chew their food but swallow it whole. Baleen or toothless whales, for example, use long hair-like structures to feed on krill and fish. Their food is later broken down across four stomach chambers.

As their bodies break this food down (via stomach acid), it produces gases, which are released as farts and eventually poo.

In fact, whale poo is one of the coolest looking in the animal kingdom. Blue whale poo can be bright orange!

Back to the top end: do whales sneeze?

The short answer, no.

Unlike us, whales need to think about breathing. When they want to take a breath, they need to swim to the surface. If they don’t, they could drown.

This means whales also sleep differently to us. They can rest different parts of their brain at a time, and take naps before rising to the surface to breathe.

And unlike us, they can’t breathe through their mouth and instead use their blowhole or nose to breath. This is like having an inbuilt snorkel on top of their head.

This makes it much easier for them to swim, breathe and eat — all at the same time. And they don’t have to worry about food going down the wrong way as their air and lung passages are separated.

We sneeze automatically and involuntarily if something tickles our nose. If whales get something caught in their noses, they could clear it using a big exhale through their blowhole, like blowing their nose. This would serve a similar function to our sneezing.

BUT, if a whale were to sneeze…

It would be big! For comparison, an adult human’s lungs can hold around six litres of air. But a humpback whale can hold over 1,000 litres — that’s a lot of bubbles!

You can actually see a whale’s breath: it’s a mixture of lung bacteria, hormones, proteins and lipids. It’s officially called “whale lung microbiota” — or whale snot — and looks like water droplets.

As a scientist, I use drones to sample whale snot to learn more about whale health.

We found the whales off Sydney didn’t even know their snot was being collected through this method. This is much safer for the whales and us as researchers as we don’t need to get close to each other.

Well there you have it, we’ve covered both ends of a whale. They’re incredible creatures who do enormous farts — thanks for the question!

Vanessa Pirotta, Wildlife scientist, Macquarie University

This article is republished from The Conversation under a Creative Commons license. Read the original article.