If the Earth is warming and polar ice is melting, how come when ice cubes in my tea glass melt the tea doesn’t run over from my glass?
While it is, generally speaking, a good practice to perform experiments for yourself and to find ways to make small scale models of large scale phenomena, there’s a challenge for both science educators and citizen scientists to understand the scale and limit of models, too. Quite honestly, rather than appearing to be a genuine question, when a question gets worded like this it sounds like an opportunity to make a fool out of scientists who have spent much of their lives studying and trying to understand how the climate works, without staking anything at risk themselves. At any moment, a piece of critical data could arrive, an experiment could be performed, that essentially invalidates and destroys everything a particular scientist has been working on, and the effect of such a discovery would be emotionally crushing. It’s simply not polite to say, “oh, here’s a nickel demonstration that proves you wrong”- even if it does do so, ultimately. You need to understand why the scientist felt there needs to be a more complicated model, and make sure that your simpler model invalidates all of the points and counterpoints that theory raised. Particularly, if the model has reached some level of consensus among hundreds or thousands of experts.
The idea that a floating ice cube in a cup melting would not raise the level of water is an obvious experiment that is very worth performing, but you should go one step further and warm the melted water to room temperature. Here’s why.
As pure water goes from freezing to about 4C, the density of the water increases. This means that a one liter block of water at freezing point will actually occupy less volume at 4C- not very much less, but enough to be measured. That’s why ice floats. So, by analogy, I’d expect that in your tea cup of ice water, the tea cup should not be predicted to overflow- rather, it would be entirely consistent with the known an established science that the volume would drop as the cube melts. Furthermore, if the remainder of the glass were filled with warmer water, and was getting cooler due to the ice, you would expect that it, too, would drop in volume.
But let’s put a pin in this- that also means if your teacup filled to the brim with water at 4C were then allowed to warm to 20 C, the density of the water would drop significantly, and the cup would very likely overflow, since it will now be about 0.2% less dense: instead of ~1000kg/m³, it is ~998kg/m³, and one liter of very cold water is now 1002ml of room temperature water.
Neither of these experiments in actuality model what is going on in the wider world: the ocean is not pure water but salt water, and the salinity of the ocean is not a constant number. Think about the cycle of weather- when snow falls and collects on the ground, the snow or ice is (essentially) pure water, and contains no salt. However, that water evaporated from somewhere, because the environment is (again, essentially) a closed system. When water evaporates from sea water, the salinity would be expected to rise- so warm tropical areas and areas which don’t get a lot of fresh water inflow would be predicted to have higher levels of salinity, since water is evaporating from these places. True to expectation, when we look at the map above, we see measured salinity in the Mediterranean is much higher than in the surrounding oceans. Likewise, areas which have a lot of snow accumulation, which we would predict to be near the polar regions, would melt and flow into the ocean, so we might expect that if there is a continual melting of water around the poles, the salinity of sea water would drop as the fresh water diluted the salinity of the oceans.
Salt water is significantly more dense than fresh water. This is why you are much less likely to drown in a salt water pool as opposed to a fresh water pool: things that are more dense sink, and things that have lower density float. So here’s another concern of ‘global warming”- if one liter of fresh water, at 1.00 kg/l and at 4C, and one liter of salt water at 35psu, 4C, and 1.03kg/l were mixed, what would be the volume of the mixture?
Since the salinity would drop in half, the new salinity is ~18 psu, and the density of the mixture is now roughly 1.01kg/l. One liter of fresh water weighs 1.00 kg, and one liter of salt water weighs 1.03 kg, so the combined weight of the new solution is 2.03kg. Dividing that by 1.01kg/l, we get 2.01 liters, an additional 10 ml of volume that wasn’t there before. And, if that solution warms, the volume will grow even further.
There’s lots and lots of effects at play. It’s not just as simple as an ice cube melting in a teacup, or fresh water into salt. Some of the effects, like ice melting to 4C, will reduce the overall volume. Others like water warming from 4C to 20C, or decreasing in overall salinity, will raise the volume. The difficulty of being a climate scientist is adding up and creating mathematical models which take into account all of those smaller factors to make estimates of what might happen in the future. Heck, the movement of ice in one location to another deforms gravity and the shape of the earth, so even if the density of sea water or the total amount of ice never changed, you could have continents pressed down an pushed underwater by the deformations of the earth’s surface.
One concern that keeps me up at night is voiced in this way- if there is a significant amount of fresh water melted from Greenland, it might be enough to stop or interrupt the circulatory flow of tropical warm water from the southern Atlantic toward Europe. If this were to happen, it would very likely cause Europe to become, on average, much colder than it has been, and significant quantities of ice might begin to collect on the continent. This would have the resulting effect of starting a new Ice Age, and would very likely result in a significant lowering of ocean levels. Good, if you happen to want to hike across the Bering Strait from Alaska into Russia, bad, if you happen to be living in northern Germany and you freeze to death under meters of ice and snow.
Our climate is not a thing that is static and unchanging- nor would anyone want this to be the case. Part of the appeal of natural beauty is the motion of the seasons- fresh wildflowers in spring, autumnal colors in fall, lazy sunshine at the beach in summer, and fresh powder on the mountains in winter for skiing. Too much of anything, and you’re either sunburned and dying of thirst or frozen to death.
It calls into question the value of property ownership- if I purchase a piece of property today, expecting the average climate to be worth X, and a different group of people change that climate to Y, do they owe me compensation of Y<X? Do I owe someone else if Y>X?
Granted, none of these matters are easily understood, measured, or predicted, and the temptation is to fall back on one of two, fatalistic opinions. First, you might become listless and not care, since over the long run we are all dead and we cannot reasonably know what is the correct answer, so enjoy whatever it is now and let nature or God sort out what happens in the future. Second, you might rely on a higher power to make these decisions for you- today, perhaps one political party wants to limit carbon emissions to decrease the rate of global warming, and tomorrow, they or a different party might want to loosen regulations on emissions to help stimulate the economy and create jobs. Neither position is necessarily incorrect, and because you were raised or happen to have a personal affinity for one political party or the other, you might believe or not believe their pronouncements as if they were the correct answer.
Both science and nature (and God, in many religions of the world) care very little for politics nor for apathetic humans. It’s always risky when one person or political party begins to wear scientific facts like a badge of certainty, since nature (or a wrathful deity) can always throw an odd meteorite your way and demolish that certainty in a flash. However, there’s very little glory in it for the people who do the hard work of taking countless measurements and calculations and attempting to better understand what the natural world is trying to tell us. One thing is certain- evidence has shown over hundreds of years that societies who use the tools of science to attempt to get better at predicting what is happening in nature appear to have better outcomes in life- they live longer, happier lives. It’s not all upwards manifest destiny, and science has contributed several ills including pollution and weapons of war which have direct, unhappy effects on people. But on a whole, if you are honest with your reckoning, there’s a lot to be said for God’s gift of mind: you have the ability not just to follow orders, but reason out what is the right thing to do, and perform small scale experiments to understand nature and the world and universe around you.
There’s a parable that preachers like to use:
A terrible storm happens, and a man hears a knock on his door. His neighbor is there, and he says “The storm is going to cause a flood- I’ve got room in my station wagon, would you like me to get you out of town?” the man replies, “No, I have faith in God, he will save me if my life is in danger”. Later, the river begins to flood, and a small stream appears and begins to flood up to the house. A local police officer speeds by on a boat, and says “Get in, this area’s going to be underwater soon!” Again he replies, “No, I have faith in God, he will save me if my life is in danger” Finally, the man is forced to go to his roof, and a helicopter arrives, and yet he turns down the offer of help a third time. Finally, the man drowns. He goes to Heaven, and meets God, where he asks “God, why didn’t you spare me? My faith is unshakeable”, to which God replies “I sent you a station wagon, a boat, and a helicopter, what more do you want?”
Science isn’t absolute truth, but there’s a lot of scientists who are warning that sea level rise might become significant within the next few decades, and we should start preparing what we are going to do when the floods come. Scientists don’t have all the answers, but spending a little less time mocking their inquiry, and more effort trying to understand the basis of their theories, is going to be to your benefit. And, if you have children, to their benefit as well.
for further reading on the fascinating backstory around ocean salinity and young-earth creationism, see The Naturalis Historia blog (part 1, 2, 3, 4).
answer originally published on Quora, at https://www.quora.com/If-water-is-denser-than-ice-why-do-sea-levels-rise-when-the-ice-caps-melt/answer/Matt-Harbowy.
matt harbowy is a scientist, activist, and data management expert. He is one of the founders of the non-profit Counter Culture Labs, working to bring fairness and egalitarian ideals to people interested in learning about science and biotechnology. He is also a top writer on the question and answer site, Quora.
