I knew that melting ice takes heat, but didn't have a good sense for how much. I decided to calculate it.

  1. Specific heat tells you how much heat it takes to increase temperature. For water, it's around 4.2 joules per gram of water to raise the temperature by +1°C.
  2. Latent heat (of fusion) tells you how much heat it takes to turn solid into liquid, while not changing temperature. For ice→water, it's 334 joules per gram of water.

So we have two different processes: water to hotter water, and ice to water. How do they compare? Let's divide 334 J/g/°C ÷ 4.2 J/g = 79.5 °C.

That means the same amount of heat can do either:

  1. Melt ice.
  2. Raise water temperature by 79.5°C (143°F).

Yow!

That's much higher than I expected. Did I do the calculation wrong? I checked specific heat and latent heat again, but I can't see anything wrong with the calculation.

Now imagine what happens with climate change. If you add heat to a system, and there's ice around, it will melt the ice. But if there's no ice around, that same amount of heat will increase the temperature by 79.5°C (143°F). eeek!!

(please tell me I did the calculation wrong, because those numbers are scary)

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2 comments:

xaminmo wrote at Wednesday, April 10, 2019 at 11:08:00 PM PDT

Amit, no, you're correct. Ice is a huge buffer. Temperature swings are more severe as ice volume decreases, because not all of that heat reaches the ice.

Going back into the ancient days of Sim Earth (actual climate models in that), you could see that as temperature goes up, weather swings become more severe.

After melting ice, the next phase change is evaporating water. Even though we don't reach boiling, molecules are bouncing balls. They are not all bouncing at the same speed. Sometimes, two crash into each other, and one flies off really fast, and the other just stops.

The increased heat causes a lot more of those to happen. Higher water vapor means more storms. All of that energy becomes convection. (Heat is really just movement). Air, including water vapor, has mass. Gigatons of mass being pushed along, seeking places where hot air rising left a low pressure area.

Higher temps mean less partial pressure of oxygen, which is more difficult on air travel, on elderly, sick, and infants, etc. The expectation is that equatorial regions will get hot enough to kill off vegetation. "Desertification". That allows surface areas to get very hot, because insolation is not diffused by plants. The soil dries up, and bakes in the heat. That causes up-drafts, which draw in more air. That air is heated up. Hot, dry air going across the top, we end up with powerful storms.

It's all pretty brutal.

Also, remember that methane is 23x the insulator that CO2 is, partly due to CH4 itself, and partly due to how it breaks down in the upper atmosphere into more greenhouse gasses. Well, we have gigatons of CH4 trapped in suboceanic ice which is melting. You can find videos of people setting fire to the surfaces of frozen lakes in Russia, and other Northern climates as funny things. Well, it happens in a lot of places in the arctic, and it's accelerating.

The runaway event has already happened. Last solar cycle was very mild compared to most of what we have recorded. We are going to have pretty serious famine, likely in our lifetime, but definitely in our kids' lifetimes. The ways to stop it now are:

* volcanic or nuclear winter, triggering a new ice age and 15C average drop
* stabilization of some form of rapid biomass growth (I'm hoping for hardy oil algae hybrids).

So much ramble, but I was just having a similar discussion at lunch today. It's spooky.



Amit wrote at Saturday, May 11, 2019 at 8:47:00 AM PDT

@xaminmo: scary :-( Yes, I too am hoping for rapid biomass growth. Volcanic/nuclear winter doesn't address CO2 acidification, but biomass would. The standard approach of reducing emissions isn't enough anymore; we have to actively take CO2 out of the atmosphere. I'm hoping we can use plankton at massive scales in large areas of the oceans that aren't especially fertile. But I'm also wondering about chemical approaches, using natural weathering processes like olivine + CO2 --> magnesite + quartz, but increasing the rate by crushing the olivine into granules to increase the surface area.