There is no “excess” heat. It is just colder water being slowly-but-steadily warmed by absorbing heat from the even-warmer water above it. More effective to put turbines in the ocean currents and let those power sources make useful energy (underwater cities?).
To make it simple for the simple for
me:
Would you say:
Yes there is more evaporation happening at the ocean, but as the atmosphere, or the atmosphere above sea level warms, it will tend to hold greater amounts of moisture so that the global total rain fall will not increase.
However, as there is more moisture in the air, when it does get released it will be more volume than in the past.
Cheers
Qazulight (This gives me a sick feeling as we would see both greater droughts as heat increases with out corresponding rain fall and floods as when it does rain it comes down in greater quantities.)
1 Like
@DrBob2
Why would anyone ignore the polar regions when trying to understand global precipitation?
It seems the polar regions would be very important in the global water cycle, as @btresist suggests, especially if they are absorbing a ton of energy as ice melts into the ocean. Sure, maybe precipitation is low in polar regions, but that is only one flow in the global water cycle.
I suppose one could choose to narrowly focus on precipitation as a discussion point, but I would think the entire water cycle would need to be considered to understand global precipitation patterns now and in the future.
1 Like
If you think of the global atmosphere as one thing, a useful mental model is a bucket under a leaking roof. The bucket is the atmosphere. The amount of water it holds depends on the size of the bucket. Warming the atmosphere means buying a bigger bucket. (Clausius-Clapeyron, Clausius is the guy who invented entropy).
The roof leaks at some rate. Eventually the bucket fills and the as roof the continues to leak, the bucket overflows. The roof leak is evaporation and the overflow is precipitation.
In this model, once the bucket fills, precipitation equals the evaporation for any bucket size. Buying a bigger bucket doesn’t change that. In this model, there is no change in global precipitation with global warming.
But the atmosphere is not a single bucket. It is a conveyer belt of buckets carried around the world, the hydrological cycle. Empty buckets are dragged along the surface filling with ocean, lake, and soil water through evapotranspiration. The winds carry the full buckets somewhere else. If the buckets are lifted high in the atmosphere, they cool, shrink (Clausius-Claperyon again) , overflow, and it rains.
If you warm the surface, you are putting bigger buckets on the conveyer belt. They fill with more water at the surface. Do they also dump out more water? That depends on how much the buckets shrink when lifted.
If warming climate also warms the cold air up high, maybe the change in bucket size from the surface to aloft is constant and rainfall doesn’t change. If the bucket size aloft doesn’t grow as much as the bucket size at the surface, then it would rain more. Warming the atmosphere also rejiggers the conveyer belt, the buckets move to different places with different temperatures and so the buckets shrink differently than they used to.
The thing about precipitation is it occurs at very small scales. Cloud microphysics scales are microns to centimeters. The bucket sizes depend on the temperature only where the bucket actually is. That’s hard to measure and hard to compute. So there’s uncertainty.
There is a lot of evidence with global warming wet regions get wetter and dry regions get drier. How much wetter and drier? Well that comes with uncertainty. The global precipitation change is the difference between the two. Subtract two numbers with uncertainty and you amplify the uncertainty.
Given all this, it’s not surprising that global precipitation changes are hard to measure.
3 Likes
I guess. However, there is evidence that snow precipitation has increased in Antarctica as the polar air temperature increases. The models are also in general agreement that there will be increased future rainfall in the region.
Precipitation has also been increasing in the Arctic since 1950, with the models projecting substantial increases going forward.
If as your link suggests the non-pole regions show no change in precipitation, while other studies indicate that the poles are increasing in precipitation that would seem to suggest that global precipitation is increasing.
Increased snowfall will offset sea level rise from melting Antarctic ice sheet (phys.org)
Antarctic rainfall could increase through 2100 - AGU Newsroom
1 Like
In the paper referenced in the OP it is because that is where we have the satellite data. 87% of the globe is covered, so you are not going to miss large trends. Also, note that precipitation is dominated by the tropics. For example, on the scale of a few years to a decade the data is dominated by ENSO (El Niño and La Niña) effects.
DB2
In theory yes, because any time you have a temperature difference you can move the energy.
So again in theory you could power a ship by temperance difference of the surface vs. deep. But the efficiency of a heat engine is determined by the temperature difference of the two reservoirs. The difference isn’t great enough to efficiently extract the energy.
Sure, but the temperature difference has to be enough to overcome the losses in the system.
Just as a guess, you’d need a long and large pipe of some kind to move that water to realize the temperature difference and the friction of that device would be far greater than the energy you’d get.
So such a device wouldn’t violate the laws of thermodynamics, but probably violates the laws of practicality at least until some new magic materials are created.
Mike
Sure, and the calculation is pretty easy. The equation for the Carnot efficiency is E = (TH−TC)/TH (temperature of the hot minus cold reservoirs, divided by the temperature of the hot reservoir).
So the ocean near surface temp is say 60 F (290 Kelvin) and the deep temperature is 35 F (275 Kelvin), the max efficiency is 5%. Not a big number.
2 Likes
I think that’s how my hot water heater works. It takes heat from the air (in my garage, which is plenty hot most of the year) and “puts” that heat into the water that is in the tank. And in return, it blows out cooler air from it’s output duct. They call it a “heat pump”. Maybe somehow energy from the warmer oceans could be used similarly?
It’s also pretty darn efficient because I know my electric bill went down by $25-35 each month after installing it.
Absolutely. A heat pump is a heat engine that works in reverse. It can be an effective way to heat something because you aren’t creating energy, you are just moving it around. But they don’t work if is really cold because there isn’t enough energy to to move.
One solution is what people often call a geothermal heat pump, but I think that name is misleading. It is really a ground loop heat pump, as opposed to an air loop. You bury the loop in the ground and it stays warm enough in the winter you can still extract the heat. You reverse the loop in the summer and you have air conditioning. Some heat pumps use groundwater for the same reason.
2 Likes
I believe yes, but defer to the excellent reply from @spinning. I especially like the idea of many buckets of water vapor distributed at small spatial scales.
Just as an aside, hurricane models divide the earth’s surface into a grid of cells that vary in size (depending on the model) but are about 10-ish km in width (NHC Track and Intensity Models). And then they also have to model a third spatial dimension that is vertical up into the atmosphere.
The most interesting part of this discussion to me is the idea of non steady state, that we can be in a long period of change in which both ocean and atmosphere are absorbing more energy because of greenhouse gas effects and then how that ever-increasing absorption of energy translates into effects on the water cycle.
2 Likes
We may have a clue. Work from Lawrence Berkeley National Lab has found that (for the US) while greenhouse gases/warming increase precip, aerosols have a long-term drying effect (and varying short-term effects).
Anthropogenic aerosols mask increases in US rainfall by greenhouse gases
Risser et al.
https://www.nature.com/articles/s41467-024-45504-8
“Our results show that the conflicting literature on historical precipitation trends can be explained by offsetting aerosol and greenhouse gas signals.”
DB2