I’ve had several requests for evidence of the hundreds of watts of downwelling infrared sky radiation. I’ve mentioned that there are many surface radiation budget observation sites around the world (but few in oceanic areas for obvious reasons). I found this presentation summarizing comparisons that Martin Wild and co-investigators have made between these measurements and the latest CMIP5 climate models at the observation sites. It is quite informative, and includes their version of the Kiehl-Trenberth energy budget diagram to fit better to the surface radiative energy budget observations.

For example, here’s a comparison for downward IR flux at the surface between the HadCM3 model and 41 Baseline Surface Radiation Network (BSRN) stations:

In this case, the model underestimates the downwelling sky radiation by about 9 W/m2. But for something supposedly “non-existent”, there is remarkable agreement between the average model behavior and the observations for this huge (300-400 W/m2) component of the surface energy budget.

What is MOST interesting to me is the existence of multidecadal changes in sunlight (downwelling shortwave) reaching the surface, as some of the sites have such records extending back to the 1930s. For example, changes at Potsdam, Germany look somewhat like how global temperatures have changed:

The authors admit this is behavior not seen in the climate models. I suppose scientists like Trenberth or Dessler would claim these changes are positive cloud feedback in response to surface temperature changes. But the continually neglected possibility is that they have causation reversed: that natural changes in cloud cover have caused the temperature changes, and cloud feedbacks are in reality negative rather than positive.

And this is where I believe we should be spending our research time in the global warming debate. Not arguing over the existence of something (“backradiation”) which is routinely measured at dozens of observation sites around the world.

I have allowed the Sky Dragon Slayers to post hundreds of comments here containing their views of how the climate system works (or maybe I should say how they think it doesn’t work).

As far as I can tell, their central non-traditional view seems to be that the atmosphere does not have so-called “greenhouse gases” that emit thermal infrared radiation downward. A variation on this theme is that even if those gases exist, they emit energy at the same rate they absorb, and so have no net effect on temperature.

I have repeatedly addressed these views and why they are false.

As far as the Slayer’s alternative explanations go, I have addressed why atmospheric pressure cannot explain surface temperature. The atmospheric adiabatic lapse rate describes how temperature *changes* with height for an air parcel displaced vertically, it does not tell you what the temperature, per se, will be.

If it was just a matter of air pressure, why is the stratosphere virtually the same temperature over its entire depth, despite spanning a factor of 100x in pressure, from about ~2 mb to ~200 mb?

For the adiabatic lapse rate to exist in the real atmosphere, there must be “convective instability”, which requires BOTH lower atmospheric heating AND upper atmospheric cooling. But the upper atmosphere cannot cool unless greenhouse gases are present! Without greenhouse gases, the atmosphere would slowly approach an isothermal state through thermal conduction with a temperature close to the surface temperature, and convection would then be impossible.

In other words, without the “greenhouse effect”, there would be no decrease in atmospheric temperature with height, and no convection. The existence of weather thus depends upon the greenhouse effect to destabilize the atmosphere.

Put Up…

The Slayers have had ample opportunity to answer my challenge: take your ideas, put them into an alternative time-dependent model for surface temperature, and run it from any initial state and see if it ends up with a realistic temperature.

Determining the actual temperature at any altitude requires computing rates of energy gain and energy loss. I spent only an hour to provide a simple version of such a model based upon traditional physics, which produces the observed average surface temperature of the Earth. It is the same physics used in many weather prediction models every day, physics which if not included would cause those models forecasts to quickly diverge away from how the real atmosphere behaves on average.

Surely, of the 200 scientists and meteorologists the Slayers claim to have at their disposal, they can produce something similar.

Here’s the equation I used for surface temperature change with time, and it assumes a single atmospheric layer with an average infrared effective emissivity of 0.9, based upon the Kiehl-Trenberth global average energy budget diagram.

I also have a version of the model which adds the time rate of change of the bulk atmospheric temperature, too, based upon the Kiehl-Trenberth diagram. These are very simple models…usually in modeling the atmosphere and ocean are divided up into many mutually interacting layers, but I’m trying to keep it simple here.

…or Shut Up

The Slayers have ample opportunity to post comments here outlining their views, often dominating the bandwidth, and those comments will remain for posterity.

But my blog is no longer going to provide them a platform for their unsupported pseudo-scientific claims…they can post their cult science on their own blog. They have taken far too much of my time, which would be better spent thinking about the more obvious shortcomings of global warming theory.

If and when they answer my challenge to provide a quantitative model of surface temperature change, I might change my mind. But they must first provide a time-dependent model like that above which involves energy gain and energy loss terms, which is the only way to compute the temperature of something from theory. Those energy gain and loss terms must be consistent with experimental observations, and (of course) the physical units of the terms must all be consistent.

But I don’t see how they can ever do that, because they will ignore the hundreds of watts of downward emitted IR radiation from the sky, an energy flux which is routinely observed with a variety of instrumentation, and explained with well-established theories of radiative transfer and laboratory evidence of the infrared absorption characteristics of various gases.

If anyone challenges me to provide justification for anything I’ve stated above, well, I assume you know how to use Google. There is abundant information out there…go educate yourself.

The satellite-based microwave global average sea surface temperature (SST) update for April 2013 is -0.04 deg. C, relative to the 2003-2006 average (click for large version):

The anomalies are computed relative to only 2003-2006 because those years were relatively free of El Nino and La Nina activity, which if included would cause temperature anomaly artifacts in other years. Thus, these anomalies cannot be directly compared to, say, the Reynolds anomalies which extend back to the early 1980s. Nevertheless, they should be useful for monitoring signs of recent ocean surface warming, which appears to have stalled since at least the early 2000’s. (For those who also track our lower tropospheric temperature [“LT”] anomalies, these SST anomalies average about 0.20 deg. C cooler than LT since mid-2002).

The SST retrievals come from Remote Sensing Systems (RSS), and are based upon passive microwave observations of the ocean surface from AMSR-E on NASA’s Aqua satellite, the TRMM satellite Microwave Imager (TMI), and WindSat. While TMI has operated continuously through the time period (but only over the tropics and subtropics), AMSR-E stopped nominal operation in October 2011, after which Remote Sensing Systems patched in SST data from WindSat. These various satellite SST datasets have been carefully intercalibrated by RSS.

Despite the relatively short period of record, I consider this dataset to be the most accurate depiction of SST variability over the last 10+ years due to these instruments’ relative insensitivity to contamination by clouds and aerosols at 6.9 GHz and 10.7 GHz.

What is the atmospheric greenhouse effect? It is the warming of the surface and lower atmosphere caused by downward infrared emission by the atmosphere, primarily from water vapor, carbon dioxide, and clouds.

Greenhouse gases and clouds cause the lower atmosphere to be warmer, and the upper atmosphere to be cooler, than if they did not exist…just as thermal insulation in a house causes the inside of a heated house to be warmer and the outside of the house to be cooler than if the insulation was not there. While the greenhouse effect involves energy transfer by infrared radiation, and insulation involves conduction, the thermodynamic principle is the same.

Without greenhouse gases, the atmosphere would be unable to cool itself in response to solar heating. But because an IR emitter is also an IR absorber, a greenhouse atmosphere results in warmer lower layers — and cooler upper layers — than if those greenhouse gases were not present.

As discussed by Lindzen (1990, “Some Coolness Concerning Global Warming”), most of the surface warming from the greenhouse effect is “short-circuited” by evaporation and convective heat transfer to the middle and upper troposphere. Nevertheless, the surface is still warmer than if the greenhouse effect did not exist: the Earth’s surface emits an average of around 390 W/m2 in the thermal infrared even though the Earth absorbs only 240 W/m2 of solar energy.

I have demonstrated before how you can directly measure the greenhouse effect with a handheld IR thermometer pointed at the sky. I say “directly measure” because an IR thermometer pointed at the sky measures the temperature change of a thermistor exposed to varying levels of IR radiation, just as the temperature of the Earth’s surface changes in response to varying levels of downwelling IR radiation.

I recently purchased a FLIR i7 thermal imager, which instead of measuring just one average temperature, uses a microbolometer sensor array (140 x 140 pixels) to make 19,600 temperature readings in an image format. These are amazing little devices, originally developed for military applications such as night vision, and are very sensitive to small temperature differences, around 0.1 deg. C.

Because these handheld devices are meant to measure the temperature of objects, they are tuned to IR frequencies where atmospheric absorption/emission is minimized. The FLIR i7 is sensitive to the broadband IR emission from about 7.5 to 13 microns. While the atmosphere in this spectral region is relatively transparent, it also includes some absorption from water vapor, CO2, oxygen, and ozone. The amount of atmospheric emission will be negligible when viewing objects only a few feet away, but is not negligible when pointed up at miles of atmosphere.

Everything around us has constantly changing temperatures in response to various mechanisms of energy gain and loss, things that are normally invisible to us, and these thermal imagers give us eyes to view this unseen world. I’ve spent a few days getting used to the i7, which has a very intuitive user interface. I’ve already used it to identify various features in the walls of my house; see which of my circuit breakers are carrying heavy loads; find a water leak in my wife’s car interior; and see how rain water flows on my too-flat back patio.

The above pair of images shows how clouds and clear sky appear. While the FLIR i7 is designed to not register temperatures below -40 deg. F/C (and is only calibrated to -4 deg. F) you can see that sky brightness temperatures well above this are measured (click the above image for full-size version).

This is direct evidence of the greenhouse effect: the surface temperature of the microbolometer within the thermal imager is being affected by downwelling IR radiation from the sky and clouds, which is exactly what the greenhouse effect is. If there was no downward emission, the sky temperature as measured by a perfectly designed thermal imager would read close to absolute zero (-460 deg. F), that is, it would measure the cosmic background radiation if the atmosphere was totally transparent to IR radiation.

Just so there is no confusion: I am not talking about why the indicated temperatures are what they are…I am talking about the fact that the surface temperature of the microbolometer is being changed by IR emission from the sky. THAT IS the greenhouse effect.

Our Version 5.5 global average lower tropospheric temperature (LT) anomaly for April, 2013 is +0.10 deg. C, down from +0.18 deg. C in March (click for large version):

Not surprisingly, the cooling appears to be confined to the Northern Hemisphere…the global, hemispheric, and tropical LT anomalies from the 30-year (1981-2010) average for the last 16 months are:

YR MON GLOBAL NH SH TROPICS
2012 1 -0.134 -0.065 -0.203 -0.256
2012 2 -0.135 +0.018 -0.289 -0.320
2012 3 +0.051 +0.119 -0.017 -0.238
2012 4 +0.232 +0.351 +0.114 -0.242
2012 5 +0.179 +0.337 +0.021 -0.098
2012 6 +0.235 +0.370 +0.101 -0.019
2012 7 +0.130 +0.256 +0.003 +0.142
2012 8 +0.208 +0.214 +0.202 +0.062
2012 9 +0.339 +0.350 +0.327 +0.153
2012 10 +0.333 +0.306 +0.361 +0.109
2012 11 +0.282 +0.299 +0.265 +0.172
2012 12 +0.206 +0.148 +0.264 +0.138
2013 1 +0.504 +0.555 +0.453 +0.371
2013 2 +0.175 +0.368 -0.018 +0.168
2013 3 +0.183 +0.329 +0.038 +0.226
2013 4 +0.103 +0.119 +0.087 +0.168

And, yes, you can try this at home.

I put together a simple surface energy balance model in an Excel spreadsheet so people can play around with the inputs. It computes the time changing surface temperature for any combination of:

1) absorbed sunlight (nominally 161 W/m2)
2) ocean mixed layer depth (does not affect final equilibrium temperature)
3) initial temperature of the ocean mixed layer (does not affect final equilibrium temperature)
4) atmospheric IR transmittance (yes, you can set it to 1 if you are carrying your sky dragon slayer [SDS] ID card)
5) effective temperature of downwelling sky radiation (nominally 283 K, but in effect becomes zero if transmittance=1)
6) surface convective heat loss (nominally 97 W/m2)

The nominal values are set to be consistent with the Kiehl-Trenberth global energy budget diagram.

The simple model is good for developing intuition about how the equilibrium surface temperature changes when varying different input parameters. I would challenge people to see what other combinations of parameters result in the observed global average surface temperature, which is believed to be around 59 deg. F or so.

Again, the model is very simple; it changes the temperature of the assumed ocean mixed layer depending upon assumed rates of energy gain and energy loss by that layer.

Here’s an example plot:

And here is the model: simple-sfc-model

Example: Nighttime cooling with and without the greenhouse effect
There’s an interesting experiment you can run with the model to see how nighttime temperatures cool off depending upon whether there is a greenhouse effect or not. If you run the model starting the surface temperature around 288 K (the observed global average), turn solar absorption off (nighttime), make the time step 1/24 of a day (1 hour), and make the ocean mixed layer approximate a land surface (set depth to 0.1 meter), you will find that the surface cools about 20 deg F overnight when the atmospheric IR transmittance is set to 0.1 (realistic), but cools by about 70 deg. F if the transmittance is set to 1 (no greenhouse effect). In other words, large amounts of atmospheric “back radiation” (admittedly a poor term) are required to explain why nighttime temperatures do not cool off more than observed.

PLEASE keep the discussion about gaining insight from the simple model…I know all about its shortcomings.

<sarc> There is an obvious conspiracy from the HVAC and home repair industry, who for years have been telling us to add more insulation to our homes to keep them warmer in winter.

But we all know, from basic thermodynamics, that since insulation conducts heat from the warm interior to the cold outside, it actually COOLS the house.

So, how in the world are we expected to believe that adding MORE insulation, which we know acts to cool the house by conduction, is somehow going to WARM the inside of the house?

After all, how can cooler insulation further heat the inside of the house? Does heat flow from cold insulation to warmer temperatures? No!

I think I’ll start a new organization to reveal this scam. Maybe I’ll call it Principia Domus International. </sarc>

FOR THOSE NOT IN ON THE JOKE: The sky dragon slayers (people who think the greenhouse effect does not exist) claim greenhouse gases cannot make the Earth’s surface warmer because those gases, distributed up through the atmosphere, are at a colder temperature than the surface. I am demonstrating a thermodynamic point which is true, no matter whether infrared radiation (in the case of the atmosphere) or insulation (in the case of the house) are involved in the energy loss. The point is this: The temperature of anything that is heated is partly governed by the nature of its cooler surroundings, because those cooler surroundings affect the rate of heat loss by the warmer object. As long as there is an energy source (the Sun), the surface temperature of the Earth can be INCREASED by reducing the rate of net energy loss by the surface.

Since the slowdown in surface warming over the last 15 years has been a popular topic recently, I thought I would show results for the lower tropospheric temperature (LT) compared to climate models calculated over the same atmospheric layers the satellites sense.

Courtesy of John Christy, and based upon data from the KNMI Climate Explorer, below is a comparison of 44 climate models versus the UAH and RSS satellite observations for global lower tropospheric temperature variations, for the period 1979-2012 from the satellites, and for 1975 – 2025 for the models:

Clearly, there is increasing divergence over the years between the satellite observations (UAH, RSS) and the models. The reasons for the disagreement are not obvious, since there are at least a few possibilities:

1) the real climate system is not as sensitive to increasing CO2 as the models are programmed to be (my preferred explanation)

2) the extra surface heating from more CO2 has been diluted more than expected by increased mixing with cooler, deeper ocean waters (Trenberth’s explanation)

3) increased manmade aerosol pollution is causing a cooling influence, partly mitigating the manmade CO2 warming

If I am correct (explanation #1), then we will continue to see little warming into the future. Additional evidence for lower climate sensitivity in the above plot is the observed response to the 1991 Pinatubo eruption: the temporary temperature dip in 1992-93, and subsequent recovery, is weaker in the observations than in the models. This is exactly what would be predicted with lower climate sensitivity.

On the other hand, if Trenberth is correct (explanation #2), then there should be a period of rapid surface warming that resumes at some point, since the climate system must eventually try to achieve radiative energy equilibrium. Of course, exactly when that might be is unknown.

Explanation #3 (anthropogenic aerosol cooling), while theoretically possible, has always seemed like cheating to me since the magnitude of aerosol cooling is so uncertain it can be invoked in any amount desired to explain the observations. Besides, blaming a lack of warming on humans just seems a little bizarre.

The dark line in the above plot is the 44-model average, and it approximately represents what the IPCC uses for its official best estimate of projected warming. Obviously, there is a substantial disconnect between the models and observations for this statistic.

I find it disingenuous for those who claim that, because not ALL of individual the models disagree with the observations, the models are somehow vindicated. What those pundits fail to mention is that the few models which support weaker warming through 2012 are usually those with lower climate sensitivity.

So, if you are going to claim that the observations support some of the models, and least be honest and admit they support the models that are NOT consistent with the IPCC best estimates of warming.

I’ve mentioned the TV tower I live next to (er…I mean “mast”), and at 1,000 1,500 ft tall it is a great lightning attractor. Since the top of the tower is up at a 60+ deg. angle, it’s a little hard on the neck to watch, so I sometimes lie down in the backyard to watch.

The severe storms that moved through town on Thursday gave me a chance to capture some lightning video with my Sony Handycam. Lightning was coming out of a thunderstorm anvil in advance of the squall line and hitting the tower before the rain arrived, a prime time for viewing. The strokes were coming every 3-5 minutes. The lightning strike I got video of started with an upward leader stroke (see the above frame grab).

In the video (below) the conducting channel of air is blown rapidly sideways by the wind, leading to a right-angle turn in the bolt at the top of the antenna. Then there’s a second stroke which reconnects more directly to the antenna, but it’s really only noticeable when individual frames are examined.

This is handheld, and I’m zoomed in pretty tight, but the Handycam’s image stabilization does a pretty good job. Oh..and turn the sound up!

After yesterday’s post about what determines temperature, I thought I would revisit one of the most convincing evidences of Earth’s greenhouse effect.

As I’ve mentioned before, a handheld infrared thermometer is a great little tool to help gain physical insight into the thermal radiative (infrared) effect the atmosphere has on surface temperature.

Here I’m going to give an example of how the IR thermometer responds to a clear sky versus a cloud, and I invite alternative ideas of what is causing the resulting indicated temperature changes.

First, I want to demonstrate how the IR thermometer does indeed respond, remotely, to the temperature of any object it is pointed at. I made the following measurements inside our break room freezer (reading about 9 deg. F), and while pointed at the coffee pot (reading about 129 deg. F):

(I’m not going to address the absolute accuracy of the measurements, which is probably not better than a few degrees, since we will be dealing with temperature changes of ten of degrees or more. If you work with these things enough you will see they are sensitive to changes smaller than 1 deg. F.)

Then, I took measurements outside our UAH building while pointing the IR thermometer at the sky. For reference, the ambient air temperature at our weather station about 100 ft away was 78 deg. F, and the dewpoint was 63 deg. F.

The thermometer is pointed first at a clear patch of sky (reading 27 deg. F), and then an adjacent cloud (reading 41 deg. F):

Now, my question is this:

What caused the IR thermometer reading to warm up by 14 deg. when it went from clear sky to the cloud?

I’m especially interested to hear an answer from those who tell me there is no such thing as downwelling sky radiation (aka “back radiation”). No matter what you believe is happening, it is rather obvious that the cloud influences the temperature reading differently than clear sky. (If you are thinking it is a reflected sunlight effect, you can perform the experiment at night and see the same effect; furthermore, the highest cloud temperatures you will get are from the thickest, *blackest* clouds on the bottom…so it’s not a reflected sunlight effect).

What Does the IR Thermometer Actually Measure?

As I mentioned in my previous post “What Determines Temperature?”, temperature is an energy budget issue, the result of energy gain versus energy loss.

Inside the IR thermometer, there is a thermopile (an electronic circuit very sensitive to temperature differences) with thermistors measuring temperature at both ends. When you point the thermometer at an object with a different temperature than the thermopile, an IR lens (which has a beamwidth of about 5 deg.) allows IR radiation to flow between the lens end of the thermopile and the target object.

If the target object is warmer than the viewing end of the thermopile, the net IR flow is from the object toward the thermopile, which begins to warm. Circuitry measures how fast those temperature changes occur and extrapolates an estimate of the target object’s temperature. (The thermometer has no idea what the infrared emissivity of the object is, so my unit simply assumes an emissivity of 0.95).

If the target object is colder than the thermocouple, the net flow of IR radiation is from the thermocouple to the object, and the thermocouple cools.

In the cloud case, the cloud has a higher emitting temperature because it is at a lower altitude, and it is more opaque in the infrared than the clear sky is.

A similar effect can be achieved from just the clear sky, by pointing the IR thermometer up at different elevation angles. Increasing temperatures will be indicated as the elevation angle is lowered toward the horizon. Today, I measured about 15 deg. F pointing straight up to about 35 deg. F when pointed about 20 deg. above the horizon.

In this clear-sky case, infrared absorbers/emitters (aka “greenhouse gases”) in the atmosphere, which are partly (but not totally) transparent at the IR frequency band the thermometer is tuned to, become more opaque as the thermometer is pointed at lower elevation angles. As the elevation angle is lowered, the path length through the atmospheric absorbers increases, and the altitudes from which the IR emission is being received are lower and thus at higher emitting temperatures.

This is the most convincing, do-it-yourself, direct observational evidence of downwelling sky radiation I have been able to find, and it makes a great little science experiment for students. What makes it “direct” evidence is that it actually measures the surface temperature effect (at surface of the thermopile) of changing downwelling IR radiation from the sky. This is the same thing happening continuously at the surface of the Earth as the strength of the greenhouse effect changes from water vapor, clouds,..oh yeah, and carbon dioxide.

And if you STILL don’t see how this demonstrates the greenhouse effect, imagine what would happen if you suddenly removed all of that atmosphere and clouds: there would be a sudden increase in the rate of net IR flow from the surface of the Earth to outer space, and temperatures would drop. THAT is the greenhouse effect.

For those who do not believe the above explanation, give us your alternative answer to the question: what causes the IR thermometer indicated temperature to increase from (1) clear sky to cloud, and (2) zenith clear sky to low-elevation clear sky?