Weather balloon measurements have been made twice daily at Desert Rock, Nevada for many years. In 1998, a surface radiation (SURFRAD) measurement facility was also installed there, which allows new kinds of analysis of how the radiation budget is affected by atmospheric profiles of temperature and humidity.

The location is arid, minimizing the influence of clouds and precipitation, making it an ideal site for analysis of downwelling infrared (IR) sky radiation and how it influences surface temperature.

A example of the main radiation components measured every 3 minutes at Desert Rock is shown in the following graph, for July 1, 1998. I have also annotated the approximate times that the radiosonde ascents are made:

There are many more measurements than this in the Desert Rock data archive, such as temperature, wind, relative humidity, barometric pressure, ultraviolet radiation, etc.

Of particular interest is the question: How does the downwelling IR intensity depend on the vertical profiles of temperature and humidity? Obviously, IR intensity depends upon temperature….but there has to be an atmospheric emitter of IR, and that is primarily water vapor.

We can examine the issue using nighttime data, so that we don’t have to deal with the huge fluxes of solar energy during the daytime. If I average the SURFRAD fluxes of downwelling IR between 00 UTC and 12Z every day, and compare them the to average of the 00 and 12 UTC radiosonde profiles in ~100 mb thick atmospheric layers, I can do correlations to see how the nighttime “sky radiation” variability is related to atmospheric temperature and humidity variability.

The results are very interesting:

The dominant influence of humidity variations on downwelling IR is clearly seen; the greater the humidity, the lower in the atmosphere the downwelling IR radiation measured at the surface originates, and thus the warmer the emitting temperatures and greater the IR intensity.

In contrast, the correlations of downwelling IR variations with temperature variations themselves are rather poor, probably because the temperature variations are so small. Clearly humidity variations dominate the downwelling IR signal, moving the effective radiating altitude up and down as humidity decreases and increases, respectively.

Now, the downwelling IR flux (the dashed line in Fig. 2, above) is what a few of our friends claim does not exist. They claim that there is no “greenhouse effect”, and that the sky (which is almost always colder than the surface) cannot emit IR in the direction of the surface because that would violate the 2nd Law of Thermodynamics.

But, of course, it is the net IR (the sum of upwelling from the warmer surface plus the downwelling from the cooler sky) which must flow from higher to lower temperature, which it does.

So, what, in their minds, is actually being “measured” by these instruments for downwelling IR? Whatever it is, Fig. 3 clearly shows it’s closely related to the humidity of the atmosphere (correlations up to 0.88 for mid-tropospheric humidity), but not very well related to temperature variations in the atmosphere. Barring some sort of conspiracy between all of the atmospheric radiation experts in the world (as well as most of us “skeptics”) it is difficult to imagine how such a “fictitious” measurement, so sensitive to atmospheric humidity, could be constructed by mistake.

But what influence do these variations have on nighttime cooling of surface temperatures? For that is how the “greenhouse effect” is usually expressed: the increase in surface temperatures caused by greenhouse gases compared to if those gases did not exist. It is not possible to answer that question in an absolute sense with measurements because we do not have a full-depth atmosphere with no greenhouse gases we can experiment on. Instead, we can only examine how surface temperature changes by relatively small amounts when the amount of greenhouse gas changes by relatively small amounts.

This can be seen in the next plot, where I have compared the change in surface temperature from 00 UTC (late afternoon) to 12 UTC (early the following morning), to the average downwelling IR during the night:

While the relationship is noisy because there are many factors governing nighttime surface cooling (wind speed, storage of solar energy in the soil during the previous day(s), etc.), we still see that the surface temperature drop during the night becomes less as the downwelling IR increases. This follows our daily weather experience that nighttime temperatures cool off more when humidity is lower, all other weather variables being roughly equal.

While the above analysis is preliminary, and there are many more relationships that could be examined (with many more years of data), the results clearly show that increasing greenhouse gas concentration in the atmosphere (in this case, water vapor) increases downwelling IR radiation from the sky, and increases surface temperature. And, while I have used nighttime data to isolate the effect from the complications introduced with daytime solar heating, it should be remembered that infrared effects on surface temperature are occurring 24 hours a day.

Downwelling IR from the sky continuously maintains surface temperatures well above what they would be without greenhouse gases (while at the same time cooling the upper atmosphere well below what it would be without those gases). Surface temperature is a function of energy gain (from the sun) and energy loss (which is reduced by greenhouse gases).

It’s not magic..it’s just physics.

NOTE TO COMMENTERS: I intend to delete any comments which include personal insults.

NOTE TO READERS OF COMMENTS: Some commenters here throw around technical terms and make grand assertions and detailed arguments which I consider fallacious. I do not have time to counter them all every time they arise, although I have addressed virtually all of them in other posts over the years.

With the climatological peak in hurricane activity only 3 weeks away, the Atlantic has been fairly quiet so far, despite seasonal forecasts of a more active than normal season.

But recent forecast model runs have been consistently predicting that a low pressure wave in the tropical eastern Atlantic will become Tropical Storm Gaston in the next 5 days or so. Then, it looks like it could intensify into Major Hurricane Gaston, with 110 kt sustained winds by Sunday evening, August 28, which would make Gaston a strong Category 3 hurricane (graphic courtesy of Weatherbell.com):

Of course this is very prelimnary, being almost 10 days out, and the system is currently not even a tropical depression yet. The predicted path of (potential) Gaston is especially uncertain. Interests along the Atlantic and Gulf coasts should monitor this system in the coming days.

As a followup to my cursory analysis suggesting increased precipitation was the probable cause of the record rise in Lake Superior water levels during 2013-2014, the GLERL folks pointed me to a relatively recent paper they published (Hydrologic Drivers of Record-Setting Water Level Rise on Earth’s Largest Lake System) which provides a detailed analysis of all of the hydrologic inputs and outputs to the levels of the separate Great Lakes (over-lake precipitation and evaporation, land precipitation runoff into the lake, river and channel inflows and outflows).

The following plot from their paper provides their statistically optimized estimates of the various hydrologic components that cause levels to change on Lake Superior. I suspect the most accurate measurements are the lake levels and outflow through the St. Marys River. Precipitation would be less well measured, and evaporation would be even more uncertain. Use the top portion to see the water level rise over the January 2013 thru December 2014 period, and use the bottom plot to understand the components that went into the rise, where arrows pointing up increase lake levels, and those pointing down decrease lake levels, compared to the long-term averages for those months (click on image for large version).

The bottom line is that the record rise in lake levels was mostly the result of above-normal precipitation (the blue [lake precip] and green [runoff from land precipitation] bars extending above the zero line). But also important was reduced evaporation (red bars) from the very cold winter of 2013-2014, which led to extensive ice cover and unusually cold lake water during the following summer.

Finally, note the grey bars, which indicate increased outflow through the St. Marys River at Sault Ste. Marie, MI, starting in mid-2013, which acted to limit the lake water rise.

As an aside, there is an interesting analogy between water storage in lakes, and heat storage in the ocean. There are inputs and outputs affecting each, and when there is a huge change (imbalance between inputs and outputs) it takes time for things to either depart from normal or go back to normal. Since the lake is small, that can happen in only a few years. In the case of heat storage in the ocean, it can take decades if not centuries for changes to be felt.

The last couple years have seen exceptional erosion along portions of the south shore of Lake Superior, especially where the ground is very sandy. The following photo was recently taken west of Whitefish Point in the eastern Upper Peninsula of Michigan, of a cabin built in the 1950s:

While water levels have been on a slow, irregular decline for decades, there was a sudden rebound during 2013-2014 to near-record high levels:

What caused this rapid rise? In fact, what controls the water level of Lake Superior on a year-to-year basis?

The hydrology depends upon many factors, both natural and human. Precipitation over the lake and the drainage basin feeding the lake, evaporation, and outflow through the rapids on the St. Marys River at Sault Ste Marie are the primary natural processes.

But locks built in the Sault in the 1800s also altered the natural lake levels, as well as contruction of a canal which feeds a hydroelectric power plant. Subsequent dredging of the shipping channels has also altered the flow. (Here’s an amazing high-resolution 1905 photo during a celebration of the locks, it still looks the same today…except for fences to keep idiots from falling in, and an observation deck).

Gates at the head of the power canal are raised and lowered to provide some human control over lake levels, and are raised to allow more water to flow out when lake levels are high. Many factors are weighed in deciding to adjust the flow out of Lake Superior, including the water level in the rest of the Great Lakes downstream, as well as Canadian concerns. The governing body for these decisions is the International Joint Commission (IJC).

For example, there has been much debate over water levels on Lake Erie, which have also been running high. If you let more water out of (much larger) Lake Superior, then the coastal interests along Lake Erie (which I suspect are much larger in number and politically more powerful) are going to be very concerned. The total population living along the lower lakes is about 15-20 times that living along Lake Superior, so you can see why interests along Superior aren’t the only ones deciding how much extra water will be allowed to flow out of the lake.

How Much Control Do We Have Over Lake Superior Levels?

Given that the Sault locks are there to stay, just how much control could we have over the water level in Lake Superior, if we wanted to?

The answer, it turns out, is not very much.

The river discharge out of Lake Superior through the St. Marys River has been running around 100,000 cu. ft./sec in the last couple of years. If you assume that we could change that rate at will by, say, 10%, and divide that into the number of square ft. covered by Lake Superior (~884,000,000,000), you will find that such a change in river discharge would only change the lake water level by 4 inches in one year. The above graph shows that much larger changes occur on the lake than this. Obviously, natural influences on water level are much larger than human influences.

I used to live on the lower St. Marys River, and can attest that when the lake level is high, so is the level of the lower river. I specifically remember the summer of 1973 (see above graph) when water on some days went up on our lawn and came close to our front door. Then, years after I moved away, low lake levels led to the shoreline going out about 100 ft. further from the house than normal.

The reason I mention this is that, when lake levels are high, there is an increase in river discharge out of the lake. That is the direction of causation: high lake levels => increased outflow. It is not: decreased outflow => high lake levels.

In other words, human manipulation of water flow out of Lake Superior is not the cause of high water levels…although we have some small amount of control to mitigate changes in lake levels, after they have occurred.

The Primary Control Knob: Precipitation

While I’m not a lake hydrology expert, I suspect that the balance between precipitation and evaporation is the governing factor in Lake Superior water level.

If we look at the average yearly precipitation departures from normal from the National Centers for Environmental Information website for the Upper Peninsula and northeast Minnesota averaged together, we find that the Lake Superior water level rises and falls depending upon excesses and deficits in precipitation:

In fact, during the most recent rapid rise in water levels, a 2-year excess in precipitation of 11 inches led to a 22 inch rise in lake levels! This is pretty spectacular.

Why would the lake rise more than the precipitation? Because the drainage basin for Lake Superior is 1.55 times larger than the lake itself, and so some of the excess water that falls on the surrounding land flows into the lake, potentially more than doubling the lake level rise due to a precipitation increase:

How well this quantitatively explains things, I don’t know. I’m ignoring changes in evaporation, which would have to be estimated through some modeling assumptions.

The bottom line is that Mother Nature is largely in control of water levels on Lake Superior. Humans can help mitigate it somewhat by adjusting flow through the St. Marys River, and I believe that is already done, but I suspect that coastal interests along the lake simply have to live with the changes, which we have very little control over.

I have sent a few questions to the experts at the Great Lakes Environmental Research Lab (GLERL), and will update this post if I find out any additional information.

In my continuing battle to keep people from being led astray by bad science, I sometimes try to think of new ways to demonstrate the existence of the Earth’s so-called greenhouse effect (GHE).

I won’t bore you with all of the many evidences I’ve already offered over the years, but instead get right to the experimental setup, which involves putting pure carbon dioxide in one tube, air in a second, identical tube, and measure how much the temperature at the bottom of the tubes cools down during a clear night. I believe that, despite the small path length of CO2, it might be possible to measure a reduction of cooling the the CO2-filled tube versus and identical tube containing air.

I would prefer to have a setup like this where the additional, incremental effect of more CO2 on the atmosphere “partially blocking the view of cold outer space” on an actual near-surface air temperature is measured. More of a real-world demonstration. It would be easier to measure how CO2 (or, say, water vapor) blocks the IR emission from a hot target in a laboratory, but that has already been measured thousands of times, to very high precision at many wavelengths and for many gases.

The widespread claim on the web that a temperature warming effect of CO2 can be measured with CO2 in a jar is totally bogus, and Anthony Watts demonstrated how Bill Nye erred in trying to demonstrate such a thing. You have to (1) have long path lengths, and (2) the CO2 must be “partially blocking” the view that a warm object has of the radiatively “cold” sky. It can’t be done inside.

The trouble with actually measuring a temperature effect from the GHE is that the broadband IR effect (over all wavelengths, not just near absorption lines) of greenhouse gases in the atmosphere really only shows up over long path lengths, so that there is appreciable amounts of greenhouse gas. These long path lengths, combined with the vertical temperature structure of the atmosphere, are necessary for the effect to become appreciable. (Right on CO2 absorption lines, the effect can be large over very short path lengths, but these very narrow bands affect only a tiny fraction of the total IR energy being transferred).

Further complicating any simple experimental setup is that the atmosphere is already pretty opaque to IR radiative transfer, making the practical measurement of a temperature change from adding a little more absorbing gas pretty difficult.

If we were to condense all 400 ppm of CO2 in the atmosphere down to the surface, it would fill a column about 4 meters deep. So, if we could fill a 4 ft tall concrete form tube with pure CO2, I calculate that would be about 120 ppm equivalent increase, or 30% increase, in CO2 compared to the total atmosphere.

The question is, would this be enough additional CO2 to change the radiative budget in the tube enough to measurably reduce the nighttime cooling at the bottom of the tube? It might be.

Of course, one could make the tube taller, and so increase the CO2 path length, but the problem is that the bottom of the tube can only see a small portion of the sky (through the top of the tube) to radiatively cool. Thats why the tubes should be lined on the inside with highly IR-reflective aluminum foil, which has IR reflectivity of 0.95-0.97. This will help the high-emissivity bottom of the tube see more of the cold sky, although multiple reflections off the walls might be required.

How might one fill the tube with CO2? Other than purchasing a cylinder and getting it filled from a supplier, one easy way might be to put a block of dry ice (solid CO2) in the bottom and just wait for it to sublimate. The cold gas will also tend to settle in the bottom, and push air out the top, maybe through a pinhole in the highly transparent (>0.9 transparency) plastic wrap cover. I calculate one 1 ft x 4 ft tube has about 0.1 cubic meter volume, which would require about 0.5 lb of dry ice to fill with CO2.

One issue is that CO2 has somewhat less thermal conductivity than air. But if you look up the numbers, you will find that the thermal conductivies involved are so tiny that they can be ignored in the energy budget of the air in the tubes. Air and CO2 are extremely poor conductors of heat.

I probably won’t attempt this till fall or winter, when air mass humidity goes down. From monitoring the Goodwin, MS SURFRAD site, I’ve noticed that the difference between upwelling IR and downwelling IR increases from only about 40 W/m2 in the summer to over 80 W/m2 on cold dry days in the winter:

One would need as big a cooling potential as possible so see the effect of adding CO2 in the tube, and that difference between upwelling IR and downwelling IR is what is important for the experiment to work. When that difference approaches zero, say with dense low cloud cover, there will be no radiatively-induced temperature change anyway.

Good insulation is absolutely necessary so that the effect of the surrounding air temperature has minimal impact on the results and the differences in tube interior temperatures will be dominated by IR radiation transfer. Insulation results in a temperature drop below ambient temperature. I have blogged previously about producing 4 deg. F temperature drops below ambient in a Styrofoam box covered with plastic wrap, and have since achieved up to 8 deg. F drop in a standard Styrofoam cooler. The effect shows up strongly within an hour or so of sunset.

The experiment would probably need to be repeated with the tubes swapped since they cannot be constructed exactly the same.

Suggestions are welcome. I’m only going to attempt things that are easy, cheap, and not time consuming.

Finally, no matter how accurately the temperature effect is that is measured (if any) it can’t be used to quantitatively estimate the effect of adding CO2 to the atmosphere. There are too many differences between the experiment and what happens when the extra CO2 is spread out through the full depth of the atmosphere, AND the atmosphere has a chance to respond through changes in clouds, evaporation, precipitation, etc. The simple experiment is meant to simply demonstrate that the GHE exists…that is, that atmospheric greenhouse gases cause a warming tendency of surface temperatures.

(Edited for clarity).

Most meteorologists consider the stratosphere to be a pretty boring place: no warm fronts, cold fronts, low pressure systems, and (almost) no clouds.

But there are a couple of things that happen there which are pretty dramatic. Sudden stratospheric warming in the polar regions is one. Another, but lesser-known, type of event is sudden temperature changes in the tropical stratosphere.

For example, in the last week the tropical middle stratosphere, as measured by channel 14 of the AMSU instrument flying on NOAA-19, has cooled by over 3 deg. C (about 5 deg. F):

The area covered is over 40% of the surface area of the Earth, so that’s a huge region.

The reason why such large temperature changes can occur in the stratosphere has to do with its vertical temperature structure, combined with dynamically-forced changes in the vertical circulation of air in the stratosphere.

The unique vertical temperature structure in the stratosphere is due to ozone being created and heated by ultraviolet solar radiation. The ozone layer then shields the air below it from UV radiation, so the layer is maintained at a “warmer” temperature as it continues to absorb UV energy.

Since the temperature increases with height in the stratosphere, any forced ascent of the air will cause a large drop in temperature at any given pressure altitude (since dry air ascent at any altitude will result in a temperature drop of 9.8 deg. C per km). Similarly, forced descent will cause a large temperature rise.

Now, the global stratosphere experiences a slow vertical circulation called the Brewer-Dobson circulation, with slowly rising air in the tropical stratosphere and slow sinking of stratospheric air outside the tropics. This circulation explains why, even though most stratospheric ozone is created in the tropics where sunlight (per square meter) is most intense, the greatest concentrations of ozone are found outside the tropics, as it is exported out of the tropical stratosphere.

Weather activity generated in the troposphere is what is believed to force this circulation (e.g., see here). As Rossby waves and gravity waves in the lower atmosphere propagate upward and equatorward, changes in their activity can cause changes in the strength of the Brewer-Dobson circulation, leading to the large temperature changes seen in the time series plot, above.

So, stronger rising of the stratospheric air is what led to cooling in the last week, but that will be almost exactly matched by warming outside the tropics where air is sinking faster than normal. (Note that rising air in one location and altitude must be almost exactly matched by sinking air elsewhere at the same altitude, otherwise there would be huge pressure differences leading to tremendous winds which will act to remove the pressure difference…this is what happens in hurricanes to some extent, where atmospheric mass is removed from the center of the hurricane faster than it can be replaced by in-flowing winds.)

I suspect these stratospheric temperature variations changes have no measurable effect on weather in the tropical troposphere, even though they might change the tropical radiative energy budget by a fraction of a Watt per sq. meter.

In less than two months (October 6, 2016) it will be 4,000 days since the last time a major hurricane made landfall in the U.S., which was Wilma on October 24, 2005.

Wilma was a record-setter, being the strongest Atlantic hurricane on record, with peak estimated sustained winds of 183 mph and lowest surface pressure of 882 mb. That surface pressure corresponds to a 13% removal of atmospheric mass in the core of the hurricane compared to normal sea level pressure.

But after the record-setting 2005 Atlantic hurricane season, with a whopping 27 named tropical storms, the bottom pretty much dropped out of hurricane activity since then.

After an unusual January hurricane this year (which I don’t meteorologically count as part of the 2016 season), we’ve had one system (Earl) that briefly achieved hurricane status before making landfall in Belize several days ago:

Will we reach October 6 without a major (Cat3 or higher) hurricane strike? No one knows. The Atlantic is quiet right now, and there has been no significant trend in global tropical cyclone activity since satellite monitoring started in the early 1970s.

Just when I thought it couldn’t get any more stupid…

Solar Freakin’ Roadways was a bad enough idea…now, the California Energy Commission has agreed to fund several projects to investigate the generation of electrical energy from piezo electric cells placed in road surfaces. The idea is that since a piezo device can convert mechanical vibrations into electricity, they can regain some of the energy lost by cars and trucks that are constantly vibrating the roads.

At first it seems like a reasonable idea…until you think about the tiny amount of energy involved compared to the cost of such devices.

While I’ve seen estimates that assume up to 40% of the energy expended by a vehicle is available for recapture, this amount is not available to produce road vibrations. Most of the energy losses are elsewhere — wind resistance, waste heat generation, friction in the driveline — and only 4% goes into the rolling resistance of the tires.

And most of THAT 4% rolling resistance is lost by generation of heat as the tire flexes….I’ll bet less than 1% goes into vibration of the road surface itself, which is what the piezo devices would be capturing a part of.

Then, what portion of that 1% could be harvested? Maybe a tenth of it? So, now we are talking about retrieving about 0.1% of the energy expended by moving cars and trucks. And that’s if the cells have 100% efficiency, which they don’t.

So, no…not “up to” 40% is available to capture by piezoelectric devices. And considering the cost of the piezoelectric cells, this would be a really bad idea…except for whatever company is getting rich off of manufacturing them.

Plus, there is the additional question of whether the devices are passively harvesting some of the road vibrational energy that would occur anyway…or would they be an active additional source of rolling resistance of the tires? If it’s the latter, then it would be ‘highway robbery‘, because it would be reducing the fuel efficiency of cars, and stealing a small portion of that extra energy required to push against the devices to convert it to electricity.

While a pilot project in the Netherlands found that Generating Electricity from Vibrations in Road Surface Works, reading of that article reveals the amount generated isn’t enough to even power a street light.

And this does not even address the practical issues involved in replacing a portion of road surfaces with piezo strips. Will it be like driving over rumble strips (see the photo above)? That won’t be very popular. What will it do to the integrity of the road surface? What if one breaks free and flies through a windshield and kills someone?

Sounds like just another energy boondoggle to me.

July Temperature Recovers Slightly from Previous Free-Fall

NOTE: This is the sixteenth monthly update with our new Version 6.0 dataset. Differences versus the old Version 5.6 dataset are discussed here. Note we are now at “beta5” for Version 6, and the paper describing the methodology is still in peer review.

The Version 6.0 global average lower tropospheric temperature (LT) anomaly for July 2016 is +0.39 deg. C, up a little from the June, 2016 value +0.34 deg. C (click for full size version):

The global, hemispheric, and tropical LT anomalies from the 30-year (1981-2010) average for the last 19 months are:

YEAR MO GLOBE NHEM. SHEM. TROPICS
2015 01 +0.30 +0.44 +0.15 +0.13
2015 02 +0.19 +0.34 +0.04 -0.07
2015 03 +0.18 +0.28 +0.07 +0.04
2015 04 +0.09 +0.19 -0.01 +0.08
2015 05 +0.27 +0.34 +0.20 +0.27
2015 06 +0.31 +0.38 +0.25 +0.46
2015 07 +0.16 +0.29 +0.03 +0.48
2015 08 +0.25 +0.20 +0.30 +0.53
2015 09 +0.23 +0.30 +0.16 +0.55
2015 10 +0.41 +0.63 +0.20 +0.53
2015 11 +0.33 +0.44 +0.22 +0.52
2015 12 +0.45 +0.53 +0.37 +0.61
2016 01 +0.54 +0.69 +0.39 +0.84
2016 02 +0.83 +1.17 +0.50 +0.99
2016 03 +0.73 +0.94 +0.52 +1.09
2016 04 +0.71 +0.85 +0.58 +0.94
2016 05 +0.55 +0.65 +0.44 +0.72
2016 06 +0.34 +0.51 +0.17 +0.38
2016 07 +0.39 +0.48 +0.30 +0.48

The July pause in cooling as La Nina approaches also happened during the 1997-98 El Nino. I’ve examined a daily time series of satellite data for 2016, and this behavior is due to intra-monthly variations in temperature, probably mostly driven by episodic deep convective activity in the tropics. Depending upon how the calendar months line up with the resulting peaks and troughs in temperature, the result is a rather irregular monthly temperature time series. It can be viewed not so much as a variation in radiative cooling to outer space, but a variation in convective heating of the troposphere.

To see how we are now progressing toward a record warm year in the satellite data, the following chart shows the average rate of cooling for the rest of 2016 that would be required to tie 1998 as warmest year in the 38-year satellite record:

Given the behavior of previous El Ninos as they transitioned to La Nina, at this point I would say that it is unlikely that the temperatures will remain above that projection for the rest of the year, and so it is unlikely that 2016 will be a record warm year in the satellite data. Only time will tell.

The “official” UAH global image for July, 2016 should be available in the next several days here.

The new Version 6 files (use the ones labeled “beta5”) should be updated soon, and are located here:

Lower Troposphere: http://vortex.nsstc.uah.edu/data/msu/v6.0beta/tlt/uahncdc_lt_6.0beta5.txt
Mid-Troposphere: http://vortex.nsstc.uah.edu/data/msu/v6.0beta/tmt/uahncdc_mt_6.0beta5.txt
Tropopause: http://vortex.nsstc.uah.edu/data/msu/v6.0beta/ttp/uahncdc_tp_6.0beta5.txt
Lower Stratosphere: http://vortex.nsstc.uah.edu/data/msu/v6.0beta/tls/uahncdc_ls_6.0beta5.txt

I continue to see some commenters here supporting the notion that the warmth of the lower atmosphere and the Earth’s surface can be explained through atmospheric pressure, rather than the so-called “greenhouse effect” (GE). The GE comes from the ability of greenhouse gases in the atmosphere to absorb (gain) and emit (lose) infrared radiation at terrestrial temperatures.

Of course, if there is no GE, then global warming cannot be caused by the addition of more greenhouse gases to the atmosphere. This view has a pretty widespread following, and I continue to get emails asking me about it.

I consider the “no such thing as a greenhouse effect” people to be wrong, and once again I will try to explain the reasons why. The GE does not contradict the 2nd Law of Thermodynamics, and without the GE, we would not even have weather in the atmosphere (more on that, below). I have written many posts covering this subject over the years, but since the issue persists, I will go over the high points once again.

WHAT CAUSES TEMPERATURE TO CHANGE?

The first thing we have to agree upon is what causes the temperature (of anything) to change: energy gain and energy loss. It doesn’t matter whether we are talking about air, the human body, a car engine, or a pot on the stove…temperature goes up when energy gain exceeds energy loss, and temperature goes down when energy loss exceeds energy gain. This is basic thermodynamics, it is how quantitative temperature changes are estimated when engineers design stuff, in weather forecast models, and in physics calculations in general. If we cannot agree on this basic point there is no reason to continue the discussion.

WHY IS THE ENERGETIC VIEW OF TEMPERATURE IMPORTANT?

The reason why we must talk in terms of an ‘energy budget’ when discussing temperature is that people tend to forget that energy LOSS is just as important as energy GAIN. For example, you cannot compute what the temperature of an object will be by shining sunlight of a known intensity on it. Yes, sunlight is virtually the only source of energy in the climate system, but the average surface temperature of the Earth cannot be estimated from the strength of this source; the processes which control the rate of energy LOSS are also involved. And the Earth’s greenhouse effect reduces the rate of energy loss by the Earth’s surface and lower atmosphere.

AIR PRESSURE

First, let’s examine the effect of air pressure. It is true that if you take an air parcel at low pressure (say, high in the atmosphere) and bring it down to the surface it will be compressed and its temperature will go up. If no heat is gained or lost to its surroundings (an adiabatic process, and we will ignore the complicating effects of water vapor condensing) the rate of temperature rise is about 9.8 deg. C per kilometer in altitude, the so-called ‘adiabatic lapse rate’.

So, if the atmosphere was continually mixed, and we ignore the effects of water evaporation and condensation, then the atmosphere would be warmer near the surface than at high altitudes, and the temperature would fall off with height at the rate of about 9.8 deg. C/km. This is the basis for the argument that it’s not the greenhouse effect that warms the Earth surface so much (and Venus’ surface dramatically more), but atmospheric pressure, instead.

But this incomplete view has a number of unexplained problems…

For example, what would the absolute temperatures be? The adiabatic lapse rate only tells you how temperature changes with height…not what the actual temperature would be. So, what temperature would you start the parcel of air high in the atmosphere at, before bringing it to the surface and warming it? Why did you choose that initial temperature? Existing theory, with the greenhouse effect, can allow you to compute that temperature from first principles.

And how to explain the effect of convective heat transfer from the Earth’s surface to the atmosphere, if the atmosphere has no way to cool itself? I think that the no-GE folks agree that there is net convective heat transfer from the surface of the earth up into the atmosphere (that’s mostly how the atmosphere get heated, by the surface). As part of this, water is also evaporated at the surface which requires energy…this energy is then released high in the atmosphere when the vapor condenses into clouds and precipitation, contributing to the convective heat transfer.

If this convective heating of the atmosphere is continuously occurring, what prevents the atmosphere from warming endlessly? It must have some mechanism of heat loss just as large as the heat gain in order for the temperature to finally settle out around some average value. The answer is that the atmosphere continuously cools by emission of infrared radiation to outer space, primarily by ‘greenhouse gases’ in the atmosphere, water vapor being the most important, and carbon dioxide being second most important.

But that IR emission occurs in all directions…not just upward. And it’s the downward emission of IR radiation that causes the greenhouse effect.

THE GREENHOUSE EFFECT

Anything that emits IR also absorbs IR, and this makes the intuitive understanding of how IR radiation affects the atmospheric temperature profile difficult. Unlike the sun, which is a single (and ultimate) source of energy, every atmospheric layer is both an emitter and absorber of IR energy. The fact we can’t see IR radiation with our eyes further impedes our intuition.

Importantly, the amount of IR energy a parcel of air absorbs is mostly independent of temperature, but the amount it emits is very dependent on temperature. The idea that air emits IR at the same rate it absorbs is, in general, just plain incorrect.

The atmosphere, even though it is colder than the surface of the Earth, emits IR toward the surface. This does not violate the 2nd Law of Thermodynamics, which only says that the NET flow of energy must be from higher temperature to lower temperature.

EXAMPLE: Think of two identical, solid plates at the same temperature facing each other. Hopefully we can all agree that there will be no net flow of IR energy between them, because they are both emitting IR at the same intensity.

Now imagine one plate is 10 deg. C cooler than the other…there will be a net flow of IR radiation from the warmer plate to the cooler plate, right?

But what if the cooler plate is 200 deg. C cooler than the warm plate, rather than only 10 deg. C cooler? Can we agree that the net flow of IR radiation will be even larger? If so, that means that the IR radiation from the cool plate to the warm plate affects the net flow of IR energy between the two plates, right? So, the colder object does effect the energy budget (and thus temperature) of the warmer object…because energy LOSS is just as important as energy gain when determining temperature.

If you want to (curiously) argue that the cold plate doesn’t actually emit energy that is absorbed by the warmer plate (as PhD physicist Claes Johnson has argued with me), you still must admit that the temperature of the cold plate DOES affect the net rate of IR transfer from the warmer surface to the colder surface, right? Well, that’s all that is required for the existence of the greenhouse effect.

And that’s what happens with the atmosphere…downward IR radiation from the sky reduces the net IR loss by the Earth’s surface, causing it to achieve a higher temperature than it would have if there was no downward radiation from the sky, and the Earth’s surface was allowed to emit IR unimpeded to the cold depths of outer space (2.7 K temperature). It doesn’t matter that the atmosphere is colder than the surface.

How do we know there is downward IR radiation from the sky?

Because it can be measured. Instruments that are selectively sensitive to IR measure changes in temperature within the instrument in response to changes in the balance between incoming and outgoing IR radiation. You can buy a handheld IR thermometer, which is sensitive to a range of IR wavelengths that are only somewhat affected by water vapor and CO2, point it directly upward at a clear sky, and it will register a fairly cold temperature. By itself, this doesn’t prove much. But if you then point it at an oblique angle (say 45 deg), it will register a warmer temperature.

Now, think about what just happened… even though you are pointed the IR thermometer at a cold target, its temperature actually went up! So, cold objects can actually make warm objects even warmer still! (If that cold object is warmer that an even colder object it replaces…like the atmosphere at a cold temperature instead of outer space near absolute zero temperature).

This is the most direct proof of the greenhouse effect I can think of. After all, what is the greenhouse effect? It is downward IR radiation from the sky causing the surface temperature to increase, compared to if that downward radiation didn’t exist. That’s exactly what happens within the handheld IR thermometer, and it is going on everywhere on Earth, all the time.

WEATHER WOULD NOT EXIST WITHOUT THE GREENHOUSE EFFECT

One of the features of a greenhouse atmosphere, which many people don’t realize, is that in addition to the lower atmosphere being warmer, the upper atmosphere is colder than it would otherwise be without the greenhouse gases. For example, addition of CO2 to the atmosphere is supposed to warm the surface, but cool the stratosphere and mesosphere. Greenhouse gases destabilize the atmosphere to the point that convection occurs, which then pushes the lapse rate toward a convective one (between dry adiabatic and moist adiabatic). This was first demonstrated with radiative transfer calculations by Manabe and Strickler (1964).

So, it is actually the destabilization of the atmosphere (net radiative warming below, net cooling aloft) by the greenhouse effect that leads to convection, clouds, and precipitation. If the atmosphere could not absorb or emit IR energy at all (a physical impossibility), and if we ignore sunlight absorption by ozone and water vapor, the atmosphere would become the same temperature as the Earth’s surface through direct conduction. This would take a very long period of time to occur, because air is such a good thermal insulator (which is why Styrofoam works so well). This kind of atmosphere is very stable, convectively, and vertical motions would largely cease (there might be some small planetary-scale motions due to the poles being cooler than the tropics.

FINAL COMMENTS

The quasi-adiabatic lapse rate observed in the atmosphere is the result of convective overturning, which itself is caused by destabilization of the atmosphere by the greenhouse effect. The lapse rate, by itself, cannot explain why the surface temperature of the Earth is what it is…it only tells us how the temperature changes with height in response to convective overturning….not what the temperature would be.

The atmospheric greenhouse effect involves radiative fluxes of hundreds of Watts per sq meter, and is included in all of the weather forecast models that are used around the world every day to forecast weather. Without the GE, the models would simply not work; you cannot ignore infrared radiative transfer in the atmosphere. Without downwelling IR radiation from the sky, nighttime on Earth would be much colder than is observed, as 300+ W/m2 of continuous cooling to outer space would cause rapid temperature drops.

Those IR effects are the basis for atmospheric temperature sounding from IR radiometers, flying since the 1980s with the HIRS instruments. The technology simply would not work if CO2 in the atmosphere was no emitting IR radiation upward and downward. The latest NASA AIRS instrument has actually measured the decrease in IR energy from the Earth as CO2 in the atmosphere has increased. This is observational evidence that an increased greenhouse effect reduces the rate of loss of IR energy to outer space, which should lead to some warming.

The IR emission by water vapor, which obscures the satellites view of the surface, can be seen in this GOES 6.7 micron image from this morning. That IR emission is occurring downward as well as upward, contributing to the greenhouse effect.

The fact that you can see the direct effects of the atmospheric greenhouse effect with even a $50 handheld IR thermometer provides further evidence that the greenhouse effect exists.

A few of the comments which will follow this post will no doubt argue against what I just presented. Fancy, technical buzzwords will be thrown around to convince you why I’m wrong. Australian Doug Cotton (who sometimes posts comments under fake names) is the leading proponent of this view. Yes, I agree with Doug that if you take a parcel of at at a certain temperature and compress it (increase its pressure), its temperature will rise…but this comes nowhere near to quantitatively explaining why the Earth’s surface temperature (or upper atmospheric temperature) is what it is.

Let me just say that, the concepts I have outlined above have been used to predict what the average temperature profile of the atmosphere looks like, from first principles and based upon laboratory measurements of the IR absorption by various gases, and they work very well (we have done this ourselves). You can run a time-dependent 1D model with an assumed atmosphere near absolute zero, or even at 1,000 deg. C, and the physics in the model (involving physcially-based energy gain and energy loss terms in every atmospheric layer) will gradually produce an average temperature profile that looks very much like that observed in the real atmosphere.

Until the no-greenhouse effect people can do the same, their hand waving arguments will be only that: hand waving arguments. And even if they could do it, how would they justify ignoring infrared radiative transfer effects in the atmosphere, which have been so well established for many years?

Finally, just because the greenhouse effect exists does not mean that global warming in response to increasing carbon dioxide will be a serious problem…that is another issue entirely, and involves things like cloud feedbacks. I’m only referring to the existence of the Earth’s natural greenhouse effect, which to me is largely settled science.

If you are interested in my many other posts on other aspects of the greenhouse effect, just enter that search term into the search box near the top of the sidebar panel to the right.