Question:
A simple question, from a simple mind?
1970-01-01 00:00:00 UTC
A simple question, from a simple mind?
Thirteen answers:
?
2011-08-23 14:17:29 UTC
Short version?

The lag is at least partly because what we're usually measuring (the air) isn't the only thing being heated up. We measure the air temperature, but the sun is also heating up the ground and the water. The ground and water will start to cool off a bit, once the time passes noon/year passes the solstice, but by cooling off, they'll heat up the air. And the sun doesn't provide a whole lot less heat until rather later in the day/year, so the heating from the ground and water will add to the heating from the sun, so the warmest point for the air is when the heating from the sun plus the heating from the ground and water is greatest, which will generally be after the point when the heating from the sun is, by itself, greatest.



For AGW, we're also measuring the ground and water, at least to some degree. The air's getting warmer, the oceans are getting warmer, and the ground is getting warmer. That means it's not just thermal lag, if it was thermal lag the oceans and ground would be getting cooler as the air warmed.



Also, there's the fact that, if you add more heat to something than it's cooling off by, it will keep getting warmer, even if you're not adding as much heat as you were before. A good analogy for this is a pot on a stove. If you have a pot on the stove, and you turn the stove to high until the water is almost boiling, then turn it to low, the temperature will continue to go up, and the pot will boil. If you time it right, you can even get it to boil after taking it off the heat entirely, because the heat already in the pot itself will finish the job. But if that were the effect happening with global warming, and it was caused by the sun, the changes would trail solar cycles in a predictable manner. To my knowledge, they're not.
pegminer
2011-08-23 09:43:58 UTC
I think this is an excellent question.



Well, it depends on where you are what the hottest time of the day is (many places is much closer to noon), and I think in most places the hottest days come closer to the solstice, but I understand your question.



Things will heat up as long as the incoming energy exceeds the outgoing energy. So during the daytime, when the sun is shining, energy keeps coming in from the sun. Some of that energy is going to heat up the ground, air, etc., which radiates away some of that energy depending on its temperature. As the sun goes down all those things that have been heated up will be radiating away energy faster than what is coming from the sun, and once the sun has set completely you just have the atmosphere (especially water vapor) sending IR downward toward the Earth. The amount of radiation is proportional to the temperature to the fourth power, so the cold atmosphere radiates less downward than the ground does upward, and the land cools down.



Now let's think about how this works with the Earth. Let's assume that the sun has been stable for many years, so that an equilibrium has been established between the incoming solar energy and the outgoing infrared energy. Then we crank up the solar output for a while, maybe several decades, does the Earth warm, or cool? It warms because now there is more energy coming in than there is going out. As the Earth warms it will radiate more IR back to space, and a new equilibrium at a higher temperature will be established. Now suppose you turn back the sun to its previous setting, what happens? Well now you have more energy leaving on average (since the Earth is now a bit warmer than it should be for equilibrium with the new solar output), and the Earth cools down. If the Earth is STILL warming, it's a clue that there is less radiation leaving the Earth for some reason (like more CO2 in the atmosphere) and conditions have changed.



Now you could argue that we are still have more solar energy coming in than going out because the sun is still sending more radiation our way than it was before, but the variation in solar output is very small and the dependence of outgoing radiation on temperature is so strong that I don't believe that can be the case. That makes it substantially different than daytime or seasonal heating, because those changes are on the order of hundreds of watts per square meter.



I will grant you and jim z that the problem is way more complicated than this, but I think that's the essence of it. People that think about this for a living, like Kevin Trenberth, could probably give you a way better answer, and I think this is a rather subtle problem that I am not an expert on. I don't really know how much you have to worry about things like the emissivity of the Earth changing with time, I'm sure people take that into account, but I'm not aware of the details.
david b
2011-08-23 09:10:12 UTC
Thermal inertia.



Edit - I think linlyons gave a great answer. Not sure why anyone would give it a TD. Simple minds I guess...
Trevor
2011-08-23 10:27:30 UTC
Going by your past questions and answers I am of the opinion that you may not be all that interested in genuine answers. However, I’ll give you the benefit of the doubt. It’s necessary to simplify this answer and omit many of the factors involved, I’ll focus on the main points.



When the Sun is at it’s highest point in the sky and the angle of incident radiation (heat) is as close to vertical as it’s going to get, then there is the maximum amount of heat energy being absorbed by the surface of the Earth.



As the hours of the day tick by more and more heat energy is absorbed and the ground gets warmer. It continues to warm for as long as there is more heat energy being received by the ground than is being lost by it.



The amount of heat in the atmosphere close to the ground is the sum of the heat coming from the Sun and from the Earth. The time of maximum temperatures occurs when an optimum is reached. So whilst heat radiated from the Sun decreases as the afternoon wears on, the amount of heat re-radiated from the ground increases and typically, on a summers day, the highest temperatures will occur at around 4pm.



Even after the Sun has set and night sets in, the ground is still radiating heat. If it’s been a hot day and the night is calm you can notice a sharp change in temperatures when moving from a field onto a road – the field has a higher reflectance and therefore absorbs less heat than the road. You may have noticed that on a night livestock often congregate on roads, all they’re doing is keeping warm.



The reason why the summer solstice isn’t the hottest day is for similar reasons. Over the course of the summer months the land and the water upon the land warms up. It will keep warming for as long as the atmospheric temperature exceeds that of the ground / water temperature.



The heat is released slowly, it would take many days for the ground to cool and many months for the water to cool. This release of heat adds to the heat from the Sun with the result that the highest air temperatures usually occur in July and August.



Because heat transfer between the aquatic and atmospheric environment is much slower, coupled with the fact that seas and oceans are generally cold and take a lot to warm them up, the maximum sea temperatures tend to occur in early Autumn (typically in October in the NH).



You mentioned the point about solar cycles. These do affect the global temperature and if there is a prolonged period of low solar activity then temperatures fall. It was 700 years of diminishing sunspot numbers, and the associated reduction in solar irradiation, that contributed to the period we know as the Little Ice Age.



Today of course we use sensitive instruments, both on the ground and in space, to measure with remarkable accuracy the amount of energy we receive from the Sun. Over the course of a year the average incoming energy is 1363 Watts per square metre; this is measured on a plane perpendicular to the Earth’s surface at the upper edge of the atmosphere.



During solar minima and maxima there is very little variation, less than one one-thousandth from the mean, the effect of which is minimal over a few years or decades. If such conditions persist for many decades or a few centuries then the cooling or warming effect is compounded and during such times the annual change in temperature can be as much as a 0.002°C. Whilst this may not sound like much, in terms of natural variation it’s extremely rapid.



Just to avoid any confusion, you state “but not on longer timescales like solar cycles”, meteorological and climatic variations cause changes on just about all time scales from a few minutes to many millions of years and all scales inbetween.
Craig Bowens
2011-08-23 08:07:47 UTC
Simple republican minds? Whatever. Anyway, it takes time for the sun to heat up the ground. At noon the sun is the most intense, but at 4:00, the sun has been warming up everything for several hours, making the temperature feel warmer. As for the summer solstice question, it's the same principle on a large scale. The ground holds heat from the sun and continues getting warmer into July. I hope this answers most of your question!
Darwinist
2011-08-23 19:13:01 UTC
I agree with pegminer; this is an excellent question, deserving of the stars.



There are some excellent answers so far, particularly from linlyons, pegminer Trevor and AMP. I cant really add to those, so I will try a different tack: A simple analogy!



It's not perfect; it does have limitations, but it is one that will be familiar to many so, hopefully, more easily understood; the graphs of y = cos x and y = sin x



http://educationalstationery.com/images/scos.gif



In a nutshell, the red curve (y = cos x) represents the path of the sun and the positive value of y its relative strength. The x axis is the horizon.



The blue curve (y = sin x) is the temperature response.



==============



I'll spell it out, in case anyone isn't quite sure ...



The y axis (x = 0) corresponds to around noon. The sun is at its highest and strongest and the temperature, though below its peak, is rising at its fastest. (the temperature curve is at its steepest)



As we progress through the afternoon, the sun gets lower and its relative strength (the forcing) gets less. Its still a forcing though, and the temperature continues to rise, but the rate is slowing. (the curve is leveling off)



As we approach 6pm (90degrees) the sun nears the horizon, the forcing nears zero and the temperature curve flattens out. Peak warming has been reached.



As the sun slips below the horizon, the forcing disappears and rapid cooling sets in, continuing through the night.



At 6am (270 degrees) the sun rises, the cooling levels out and temperatures start to rise again, but only slowly at first as the strength of the sun is still relatively low.



As the morning progresses, the sun gets higher, the strength of the forcing increases and the temperature rises more rapidly in response.



At noon the cycle starts again.



======================



As I said, this model could be improved, but it illustrates the main points, and I think it gains something for its simplicity. Hopefully it explains the first part of your question.



Regarding the question of the lag after the solstice, it's basically the same idea as above.



The difference is that there is a very large change in forcing between day and night, and a very rapid initial temperature response. When looking at (say) a year, the days and nights aren't really relevant; we just average them out. The change in forcing between summer and winter is less than that for days/nights and the rate of change is much slower, as is the response.



It's the same again for the solar cycle. It's not correct to say that there is no time lag for the solar cycle, it's just that the change in forcing over a cycle is so slight that the response would be negligible.



It would be as a ripple on the shoreline; swamped by the waves of day/night, the tide of summer/winter and the Tsunami of El Nino!



Don't get me wrong, I'm not saying a succession of weaker or stronger solar cycles wouldn't have some effect on temperature, but the change over a single cycle, I'd be surprised if it was even detectable.



Please see my answer in the question referenced by AMP for further details.



https://answersrip.com/question/index?qid=20110615120328AAQh1XY
2016-05-14 23:52:51 UTC
Don't worry, you're not weird! I think it's mainly due record companies jumping on whatever trend is going at the moment, packaging it in a lovely "mainstream" way that is easy for the mindless masses to blindly follow and then make a huge profit out of it all! If rock and metal were left to follow it's own course instead of being used to make profit, I think we'd all be listening to a lot better stuff! Unfortunately, rock and metal has become the in thing since Nirvana killed off all the old school metal, and then Nu Metal took over. Since then it seems to be nothing but Emo, Screamo, totally wet rock (or should that be pop bands?) crappy punk bands and bands that seem more concerned with their image than their music!! I'm sure the people you ask who their favorite bands are, will in a few years time, tell you a completely different list of bands, because their musical taste will have shifted to whatever is trendy at that point in time! If it weren't for bands such as Lamb of God, Trivium etc, the whole metal scene would be f*cked!! But that's just my opinion!!
?
2011-08-23 08:06:05 UTC
If I understand the question right, it would be because the earth is on a 23 degree till (i think) and when orbits around the sun, it causes the seasons. The way the earth sits on the hottest day of the year (for where ever you live) causes the earth to be hit more directly rather than at an angle causing the rays hitting the earth to be more focused, a therefor heating that part of the earth more efficiently. The hottest part of the day for where you live is the coldest part of the day for someone one the other side of the earth.
spikeychris
2011-08-23 09:01:05 UTC
your lack of understanding about the solar system is astounding but anyway. The solar maximum and solar minimum that people talk about relates to sun spot activity. Increased sun spot activity leads to increased solar flares which leads to increases in the amount of solar energy that reaches the planet.



There are a multitude of reasons why the summer solstice is not the hottest day of the year and its mainly down to cloud cover but also has a lot of to with wind patterns. But anyway the amount of solar radiation that the planet recieves changes over time and goes in cycles. The sun does have an impact on climate anyone who says otherwise is talking rubbish however the current cause of climate change is not the sun because the sun has not changed significantly enough to make a difference and has kept constant cycles for a very long period of time.



The other thing is there is a big difference between the temperature at ground level and the temperature in the atmosphere and greenhouse gases trapping heat in the atmosphere are the main problem of global warming (they are essential for life on this planet but too much of them are a bad thing for us).
A Modest Proposal
2011-08-23 13:41:12 UTC
Yes, with any system you would expect a lag between forcing and the equilibrium temperature being achieved. Your analogy works, but you'd have to have some sort of numerical context to tell how far it really applies.



Total TSI does not vary by much between minimums and maximums, only about one watt/m^2. Take, for starters, a TSI reconstruction summary (and extension of the SATIRE-T model) published by Vieira et al in Astronomy and Astrophysics earlier this year:

http://cc.oulu.fi/~usoskin/personal/aa15843-10.pdf



As you can tell from their Figures 5 and on, TSI kept within a range of roughly under two watts per meter squared throughout the whole Holocene. The total TSI variance during the last three centuries, as can be seen well in Figures 1 and 8, nicely displays the TSI rise during the beginning of the twentieth century, and the leveling/drop starting a bit after mid-century. Before that, TSI was either falling or somewhat level for 60-70 years, there was a dip from the 1700s to the 1800s, and TSI rose from 1700 to when that first dip occurred.



Before we get into just how long the lag is, it might help viewing the forcing from a temperature perspective as well. The timeframe during which TSI did rise that I think we can agree is actually pertinent to the warming we've observed during the twentieth century, which is during the twentieth century, saw an increase of about 0.75 W/m^2 (going off of Figure 8). As TSI is *not* a measure of the radiation that is actually absorbed by the Earth at a given point but the top of atmosphere intensity, if we want an averaged value of increased forcing then we need to take into account spherical geometry (only a hemisphere ever faces the Sun at once; its base, which is the cross-section facing the Sun, is a circle) and albedo. The circle dissecting a sphere is a fourth of its surface area, and the Earth's average albedo reduces its absorptivity to about 70% of a black body. So:



∆F = 0.7*0.25*∆TSI



So the change in forcing, from a TSI rise of 0.75 W/m^2, would be about 0.13 W/m^2. If we accept an equilibrium climate sensitivity (ECS) of 3˚C per 2xCO2 forcing equivalent (about 3.7 W/m^2), then that translates into a temperature change of about 0.11˚C (equilibrium, mind you) temperature change from such a forcing. So, even if there was a lag, and all of that warming is now being recognized or was recognized over the past ~40 years, it is very little. Taking into account transience (the lag), you would expect a 2˚C TCS and about 0.07˚C of that warming by the time it peaked. That leaves very little warming to occur during the last 40 years.



Now, as to if the lag can even be this long, I pose this question: why was there not a similarly long lag in temperature as a response to the falling/level TSI prior to the temperature rise during the early twentieth century? Again, the TSI started to rise almost concomitantly with temperature, it did not precede it by 40 some years. What did precede it (the warming) by 40 some years was a period of relative stability in TSI.



From a basic thermodynamic perspective too, one would expect a shorter lag in response to a smaller change in forcing. Again, ∆TSI and ∆F are quite small, so a 40 year lag seems excessive.



As a side note, whether Trevor is right or not in presuming you may not want to hear actual answers, I think it does pose an interesting point and is one related to a topic of a question I previously asked, about just how long the lag is for solar forcing. I didn't get particularly specific answers (of course, I didn't provide specifics too), but in case you want to have a look:

https://answersrip.com/question/index?qid=20110615120328AAQh1XY
JimZ
2011-08-23 08:50:08 UTC
Even in answering your question, Craig doesn't seem to understand the point. For those who view the climate as if it were in a simple system that can be easily modeled and understood, your question probably doesn't make much sense. For the rest of us that understand that the climate isn't a simple math formula it does make sense. We live in a period of time that the sun is relatively intense. Deniers of facts (alarmists) like to pretend otherwise. Similar to an Indian summer, I don't see why we can't have some warming when other factors such as ocean currents favor it even when the sun appears to have started a cooling cycle but that remains to be seen IMO.
?
2011-08-23 08:02:44 UTC
I can not answer your question,. and honestly no one else can either. We know so little about space, and earth. If global warming is such an issue, why are the lower states installing heat systems. In Mexico record colds?
2011-08-24 09:22:19 UTC
So, in a nutshell, it appears that they agree with you that AGW CO2 theory is a bit weak.


This content was originally posted on Y! Answers, a Q&A website that shut down in 2021.
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