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Comment by hattmall | Hacker News Reader

2x the landmass is in northern hemisphere, so there's less moderation from evaporation in NH summer.

OK the landmass thing a few people pointed out. I can buy into this, but it's still a bit confusing.

What does 'moderation' mean? The solar energy has to go somewhere, I'm assuming that's temperature. Are you saying it's not going into temperature, but instead being stored some otherway (like evaporation causing an increase in potential energy as the molecules rise?).

To me it's a question of energy input from sun - energy reflected and radiated out. Something like

   temperature = constant * (energy from sun - energy reflected - energy radiated)

Maybe the earth reflects more energy due to more water / less land in the southern hemisphere?

Antarctica is a huge white block of ice too. That reflects a lot of sunlight.

It's more that every substance has a specific heat capacity. That is, how much energy it takes to raise 1 g of that substance one degree Celsius.

Water happens to have some of the highest specific heat capacities. Therefore, the south can "store" more energy in the hot months, and release that same energy in the cool months better than the north can

Yep forgot about this, explanation makes perfect sense. Thank you.

Thank god we have these big wet heat sinks available to help keep climate stable.

There is actually an energy cost to evaporation which takes some of that energy: https://en.wikipedia.org/wiki/Enthalpy_of_vaporization

So, this, as well as ocean mixing is how the surface temperature is "moderated", in addition to the heat capacity that others have brought up.

Aha thank you this was my eureka moment. I remember from high school chemistry the idea that temperature stays constant when energy input goes to phase change.

So in the southern hemisphere with that much water, some of the energy goes into the phase change between water/steam. Much less so in the northern hemisphere.

Thank god we have these big thermal sinks (ice/water) to hold a lot of this energy to keep temp a little more stable.

Follow up question: I'm assuming the exact same thing applies with ice->water. So some of the energy hitting the earth is going into melting the ice instead of increasing temperature. It would seem to follow that, once all the sea ice and glaciers have melted, that this phase-change effect is removed, and therefore the temperatures will increase faster as none of the excess energy is going into ice->water phase-change?

Do they predict the temperature rise to increase once all of the sea ice and glaciers have melted?

Or maybe once it's water it just means that there is that much more liquid water available to evaporate into humidity?

Also, anyone know how the Canadian wildfires impacting the equation? Is that a potential explanation for the several sigma deviation this year?

> It would seem to follow that, once all the sea ice and glaciers have melted, > that this phase-change effect is removed, and therefore the temperatures > will increase faster as none of the excess energy is going into ice->water > phase-change?

Yes, and it's even worse than that. The ice also reflects and awful lot of energy back into space due to being highly reflective. When that the ice is gone, that exposes darker surface which is a lot less reflective. That will also result in lot more heating.

The more things warm up, the more things will warm up in a vicious cycle with many positive feedback loops. Sadly a lot of it seems irreversible at this point.

More desert dust being carried at higher altitudes - Himalayas, Alps - is also increasing the darkness aka heating of the glacier surfaces, thus speeding their melting...

This is more complicated than you can get into with a few comments but your basic assumptions are incorrect. To overly simply more land on northern hemisphere, but it’s also a question of ocean currents and the distribution of land etc.)

The first assumption is there’s a linear relationship, this is false. Also, X energy always moves from X to Y temperature, this also false. (https://en.wikipedia.org/wiki/Specific_heat_capacity etc)

Also it seems like energy reflected/radiated should be a constant or even a direct function of temperature, this is also false. (https://en.wikipedia.org/wiki/Albedo etc)

Undergraduate thermodynamics is complicated, but Earth is even more so because energy moves around quite a bit and the atmosphere is complex. Wind and ocean currents make a huge difference, as do cloud cover, and …

It's not

  temperature = constant * (energy from sun - energy reflected - energy radiated)

Temperature is precisely what leads to 'energy radiated' after all (see: black body emission).

Temperature is not 'the leftover energy'. The Earth is broadly in equilibrium.

It's more like

  delta_temperature = constant * (energy from sun - energy reflected - energy radiated)

Any imbalance between energy in and energy out is what manifests as increase or decrease in global temperature.

This Veritasium video gives a good idea of what we do get from the sun, if not 'net energy in': https://www.youtube.com/watch?v=DxL2HoqLbyA

The whole picture is more complex, as others are pointing out, but sticking just to evaporation - the point is that more energy in can lead to more humidity at the same temperature. Phase changes like evaporation consume energy without increasing temperature. Land masses don't experience phase changes at regular temperatures reached on the earth, so more energy in just leads to higher temperatures.

Check this website for good and detailed explanations of climate related stuff: https://www.climate4you.com/

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