Antarctic Sea Ice Extent

[Alpha5]

The anomaly is still smaller than the NH one, but its still impressive nonetheless. 

[Snow_Miser]

Looks like Antarctic Sea Ice is currently the second highest on record. Interesting.

[PhillipS]

Looks like Antarctic Sea Ice is currently the second highest on record. Interesting.

2nd highest by what metric?  Here are the current CT charts for antarctic SIA and anomaly:

 

 

 

 

[ORH_wxman]

2nd highest by what metric?  Here are the current CT charts for antarctic SIA and anomaly:

 

 

2nd highest SIA for the date....from the same source:

 

 

 

 

 

 

 

http://arctic.atmos.uiuc.edu/cryosphere/antarctic.sea.ice.interactive.html

[ineedsnow]

you do realize that they are almost at the end of there summer down there

2nd highest by what metric?  Here are the current CT charts for antarctic SIA and anomaly:

 

 

 

 

[PhillipS]

you do realize that they are almost at the end of there summer down there

 

Yes, I do realize that it is summer in Antarctica.  What I didn't realize was that they were talking about a SIA value that was 2nd highest for that given day.  Silly me, I thought they were talking about long-term climate when in fact they were talking about short-term weather.

[The_Global_Warmer]

Nasa has already spoken about winds being the culprit.

 

 

It looks like it's not effecting regional sst's least in a negative way.

 

The extreme lack of any detailed analysis show's the "propped" up nature of this thread. 

 

No talk of weather patterns, predictions, no mention of the regions of where the "extra 20 CM of ice is located".

[ORH_wxman]

Nasa has already spoken about winds being the culprit.

 

 

It looks like it's not effecting regional sst's least in a negative way.

 

The extreme lack of any detailed analysis show's the "propped" up nature of this thread. 

 

No talk of weather patterns, predictions, no mention of the regions of where the "extra 20 CM of ice is located".

 

 

I don't think anyone has a very good handle on why the Southern Ocean is cooling the past 30 years. There's some theories, but nothing very concrete.

[The_Global_Warmer]

I don't think anyone has a very good handle on why the Southern Ocean is cooling the past 30 years. There's some theories, but nothing very concrete.

 

That is true.  But I referring to the ice pack it self.  While of course the Southern Sea Ice is important.  I am not making any argument saying it's not.

 

Now in terms of energy imbalance we know because of ice composition/radiative physics that the Northern Ice has a much larger effect on the energy budget.  Not only is the coverage difference less.  It's very thin ice.  So it's work on keeping energy out right now is poor.  It's likely not this high because of temperatures "cooling above it".  Hence the wind explanation. 

 

My beef then is the vague talk of it.  specifically when it's abnormally high by people who want to convoluted the two poles as if they are equal in importance in regards to sea ice when nearly every thing about them is different.  That's where the idea of this being a drive by topic to over-shadow the Northern Sea Ice comes from.

 

I would love an equally in depth conversation if there can be one about the Southern Ice, but like mos people I am far more interested in SSTs and Land ice when it comes to the South Pole.  We would need to see some very large changes in sea ice thickness/coverage for it to have an important impact on energy imbalance because of the ocean depth/lack of mixing of heat and so on.  it's a very refined clockwork system that we seemingly do not fully understand.

 

Now to SSTs...I dont have SST data back any earlier than this but looking at the PDO it seems a bit strange.

 

I am sure this has been covered but it looks like a hell of a correlation to the PDO for Southern Ocean SSTs (60-90S)

 

 

Do they follow the PDO or the other way around in terms of happening. 

 

 

 

SST have rocketed for the moment up to .20 last week for the Southern Ocean.

 

Now will we see the PDO go positive for a bit?

[SVT450R]

I think part of the reason why not much discussion in here is that you're constantly told it means nothing most of the time.  When in reality we should dig into discussion on whats going on at both poles equally and not sit and hug one side as if it dictates the entire globe.

[The_Global_Warmer]

I think part of the reason why not much discussion in here is that you're constantly told it means nothing most of the time.  When in reality we should dig into discussion on whats going on at both poles equally and not sit and hug one side as if it dictates the entire globe.

 

 

In terms of Southern Sea Ice, there is plenty of research and data out there.  We have ITP's down there too and the Australians for example have taken dozens, if not (iirc) 50-80 research expeditions since the 80s or maybe even further back I believe.

 

 

The thing is this.  That is very thin.  Almost all FYI and most of it is is not even a Meter thick.  really, over half of it is not even a half a meter thick.  So when you have anomaly's that are not very large.  running 200-600K at the most in normal times over mostly deep ocean that doesn't have much mixing.  The albedo effect's are not significant at all. 

 

 

 

Antarctic sea ice thickness is a difficult parameter to measure over large areas because there is still no satellite instrument that accurately measures it. This paper reports on a compilation of ship-based observations of sea ice (and snow cover) thickness, collected on 83 Antarctic voyages between 1980 and 2005.

The data have been compiled to give this circumpolar map of the mean annual sea ice thickness around Antarctica. They have also been analysed to give statistics on regional and seasonal changes.

This is the first published climatology of Antarctic sea ice and snow cover thickness for the Antarctic is valuable for:

• developing and checking climate models, and for
• long-term assessment of changes in sea ice cover around Antarctica.

 

 

 

[1] Ship-based observations are used to describe regional and seasonal changes in the thickness distribution and characteristics of sea ice and snow cover thickness around Antarctica. The data set comprises 23,373 observations collected over more than 2 decades of activity and has been compiled as part of the Scientific Committee on Antarctic Research (SCAR) Antarctic Sea Ice Processes and Climate (ASPeCt) program. The results show the seasonal progression of the ice thickness distribution for six regions around the continent together with statistics on the mean thickness, surface ridging, snow cover, and local variability for each region and season. A simple ridge model is used to calculate the total ice thickness from the observations of level ice and surface topography, to provide a best estimate of the total ice mass, including the ridged component. The long-term mean and standard deviation of total sea ice thickness (including ridges) is reported as 0.87 ± 0.91 m, which is 40% greater than the mean level ice thickness of 0.62 m. Analysis of the structure function along north/south and east/west transects revealed lag distances over which sea ice thickness decorrelates to be of the order of 100–300 km, which we use as a basis for presenting near-continuous maps of sea ice and snow cover thickness plotted on a 2.5° × 5.0° grid.

 

http://www.atmos.washington.edu/~sgw/PAPERS/1993_seaice.pdf

 

 

 

Characteristicso f springtimes ea ice off East Antarcticaw ere investigatedd uring a cmise of the

Australian National Antarctic Research Expedition in October through December 1988. The fractional

coverage of the ocean surface, the ice thickness, and the snow cover thickness for each of several ice

types were estimated hourly for the region near the ship. These observations were carried out

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at 0.5 to thec oasot f Antarctica.T hel ow averagael bedois in partd uet o thel argef ractiono f openw ater

withint hep ack, but extensivfer actionso f almosts now-freteh in ice alsop lay an importanrto le.

 

 

While of course the ice pack plays a large and important role.  The "changes we have seen have not caused any sort of extensive feedback changes like the rapid changing arctic ecosystem for many reasons.

 

I would fully expect changes on the land ice(like melting) or sst changes have larger impact's than the sea ice numbers down South.

 

We are not seeing widespread 8-12C sst anomaly's(hitting up to 20C in the SOO and North of Alaska, these are monumental changes, or rapid weather pattern changes like we have seen in the arctic likely due to massive changes in energy in vs out and how it effect's the atmosphere. 

 

 

We haven't seen an inverse or similar near complete destruction or building up of anything down there like we are seeing in the arctic, which isn't just sea ice, it's land ice that has also started to rapidly go and snow cover in Spring has rapidly changed.

[Snow_Miser]

[Snow_Miser]

A pretty important paper that was just published concerns trends in Antarctic Sea Ice.

 

With Stratospheric Ozone Depletion over Antarctica, and an increase in the concentration of Greenhouse Gases, the CMIP5 models predict an overall decrease in Antarctic Sea Ice. The opposite of what has been observed. Thus, there are factors missing from the models that cause them to incorrectly simulate trends in Antarctic Sea Ice. This paper also refutes claims that stratospheric ozone depletion is responsible for Antarctic Sea Ice increase.

 

http://onlinelibrary.wiley.com/doi/10.1002/grl.50578/abstract

 

From the paper:

 

"The recent observed positive trends in total Antarctic sea ice extent are at odds with the expectation of melting sea ice in a warming world. More problematic yet, climate models indicate that sea ice should decrease around Antarctica in response to both increasing greenhouse gases and stratospheric ozone depletion. The resolution of this puzzle, we suggest, may lie in the large natural variability of the coupled atmosphere–ocean-sea-ice system. Contrasting forced and control integrations from four state-of-the-art models, we show that the observed Antarctic sea ice trend falls well within the distribution of trends arising naturally in the system, and that the forced response in the models is small compared to the natural variability. From this, we conclude that it may prove difficult to attribute the observed trends in total Antarctic sea ice to anthropogenic forcings, although some regional features might be easier to explain."

[AvantHiatus]

 

Skeptic arguments that Antarctica is gaining ice frequently hinge on an error of omission, namely ignoring the difference between land ice and sea ice.

In glaciology and particularly with respect to Antarctic ice, not all things are created equal. Let us consider the following differences. Antarctic land ice is the ice which has accumulated over thousands of years on the Antarctica landmass itself through snowfall. This land ice therefore is actually stored ocean water that once fell as precipitation. Sea ice in Antarctica is quite different as it is generally considered to be ice which forms in salt water primarily during the winter months. 

In Antarctica, sea ice grows quite extensively during winter but nearly completely melts away during the summer (Figure 1). That is where the important difference between antarctic and arctic sea ice exists. Arctic sea ice lasts all the year round, there are increases during the winter months and decreases during the summer months but an ice cover does in fact remain in the North which includes quite a bit of ice from previous years (Figure 1). Essentially Arctic sea ice is more important for the earth's energy balancebecause when it melts, more sunlight is absorbed by the oceans whereas Antarctic sea icenormally melts each summer leaving the earth's energy balance largely unchanged.

 

 

 

http://www.skepticalscience.com/antarctica-gaining-ice.htm

 

http://www.nature.com/news/global-warming-expands-antarctic-sea-ice-1.12709

[Snow_Miser]

 

http://www.skepticalscience.com/antarctica-gaining-ice.htm

 

http://www.nature.com/news/global-warming-expands-antarctic-sea-ice-1.12709

 

I think there is some controversy with regard to if the Land Ice is shrinking or expanding. Will (ORH_wxman) posted a link from Zwally et al. that showed that Land Ice Gains exceeded land ice losses. I also posted a few studies backing that up as well.

 

Munneke et al. 2012 published this interesting chart:

 

 

This chart shows the total meltwater volume for various regions in Antarctica on the bottom half of the image, and the total melt on the top part of the image. As you can see, there is no trend in the Meltwater Volume. If anything, it has slightly declined over the last 30 or so years.

 

From the paper:

 

"Surface snowmelt is widespread in coastal Antarctica. Satellite-based microwave sensors have been observing melt area and duration for over three decades. However, these observations do not reveal the total volume of meltwater produced on the ice sheet. Here we present an Antarctic melt volume climatology for the period 1979–2010, obtained using a regional climate model equipped with realistic snow physics. We find that mean continent-wide meltwater volume (1979–2010) amounts to 89 Gt y⁻¹ with large interannual variability (σ = 41 Gt y⁻¹). Of this amount, 57 Gt y⁻¹ (64%) is produced on the floating ice shelves extending from the grounded ice sheet, and 71 Gt y⁻¹ in West-Antarctica, including the Antarctic Peninsula. We find no statistically significant trend in either continent-wide or regional meltwater volume for the 31-year period 1979–2010."

[Snow_Miser]

Amazing how much less traffic this thread receives than the Arctic Sea Ice Thread. Pretty remarkable.

 

[PhillipS]

Amazing how much less traffic this thread receives than the Arctic Sea Ice Thread. Pretty remarkable.

 

 

 

I'm amazed you find that amazing.  Climatologists have reported for years that Antarctic sea ice is slowly increasing at a rate of around 0.1 M km2 per decade.  Several reasons for this have been given including, IIRC, reduced surface salinity due to meltwater from the Antarctic ice sheet, and the effects of the ozone hole.

 

Remember, the increase in the Antarctic SIA maximum doesn't have much affect globally because the maximum occurs during the time of least insolation - therefore very little albedo effect.

 

Was there something in particular about Antarctic sea ice you found mind-blowing?

[ben4vols]

I'm amazed you find that amazing.  Climatologists have reported for years that Antarctic sea ice is slowly increasing at a rate of around 0.1 M km2 per decade.  Several reasons for this have been given including, IIRC, reduced surface salinity due to meltwater from the Antarctic ice sheet, and the effects of the ozone hole.

 

Remember, the increase in the Antarctic SIA maximum doesn't have much affect globally because the maximum occurs during the time of least insolation - therefore very little albedo effect.

 

Was there something in particular about Antarctic sea ice you found mind-blowing?

 

If the blue line on his graph was well below the gray line, I'm sure this thread would be a bit more popular.

[GaWx]

I'm amazed you find that amazing.  Climatologists have reported for years that Antarctic sea ice is slowly increasing at a rate of around 0.1 M km2 per decade.  Several reasons for this have been given including, IIRC, reduced surface salinity due to meltwater from the Antarctic ice sheet, and the effects of the ozone hole.

 

Remember, the increase in the Antarctic SIA maximum doesn't have much affect globally because the maximum occurs during the time of least insolation - therefore very little albedo effect.

 

Was there something in particular about Antarctic sea ice you found mind-blowing?

 

1) Why shouldn't the Antarctic ice albedo have about as much effect as the Arctic ice albedo?

 

2) IF the Antarctic ice really is increasing due to meltwater as you say (I don't know that that is true but if it is), might that act as a natural negative feedback to warming? In other words, global warming causes increased meltwater, which decreases salinity, which raises the freezing point, which increases ice, which increases albedo, which lowers temp.'s back down? Are models even capable of properly taking these kinds of things into account?

[ORH_wxman]

1) Why shouldn't the Antarctic ice albedo have about as much effect as the Arctic ice albedo?

 

2) IF the Antarctic ice really is increasing due to meltwater as you say (I don't know that that is true but if it is), might that act as a natural negative feedback to warming? In other words, global warming causes increased meltwater, which decreases salinity, which raises the freezing point, which increases ice, which increases albedo, which lowers temp.'s back down? Are models even capable of properly taking these kinds of things into account?

 

 

The antarctic sea ice extent around the solistice is less than that of the arctic...usually about 9-10 million sq km in the arctic and around 7 million sq km in the antarctic. So that would point to less albedo effect of the antarctic sea ice. 

 

The overall albedo of the antarctic is greater though since you have to include the huge land ice cap...but if we are just measuring the sea ice, then the antarctic effect should calculate out to be less.

[GaWx]

The antarctic sea ice extent around the solistice is less than that of the arctic...usually about 9-10 million sq km in the arctic and around 7 million sq km in the antarctic. So that would point to less albedo effect of the antarctic sea ice. 

 

The overall albedo of the antarctic is greater though since you have to include the huge land ice cap...but if we are just measuring the sea ice, then the antarctic effect should calculate out to be less.

 

Will,

1. Thank you for the info. So, the Arctic has about 2-3 million sq km more ice at solstice.

 

2. Do you happen to know anything about this?:

 IF the Antarctic ice really is increasing due to meltwater as Phillip says (I don't know that that is true but if it is), might that act as a natural negative feedback to warming? In other words, global warming causes increased meltwater, which decreases salinity, which raises the freezing point, which increases ice, which increases albedo, which lowers temp.'s back down? Are models even capable of properly taking these kinds of things into account?

[ORH_wxman]

Will,

1. Thank you for the info. So, the Arctic has about 2-3 million sq km more ice at solstice.

 

2. Do you happen to know anything about this?:

 IF the Antarctic ice really is increasing due to meltwater as Phillip says (I don't know that that is true but if it is), might that act as a natural negative feedback to warming? In other words, global warming causes increased meltwater, which decreases salinity, which raises the freezing point, which increases ice, which increases albedo, which lowers temp.'s back down? Are models even capable of properly taking these kinds of things into account?

 

 

I don't know a lot about #2. The theory sounds plausible. We do know that the Southern Ocean as a whole around Antarctica has been cooling for 30+ years based on satellites which is my personal guess for antarctic sea ice increasing, but maybe that is somehow tied back into land ice melting.

 

The problem is we don't know all that much about the magnitude of land ice melt on Antarctica. There's quite a few studies that produce different results and often the error bars are larger than the magnitude of their results.

 

 

Its an interesting topic though...esp since so much potential sea level rise is locked up in Antarctica. An order of magnitude more than Greenland, so obviously its potential impact is far greater.

[Snow_Miser]

I'm amazed you find that amazing.  Climatologists have reported for years that Antarctic sea ice is slowly increasing at a rate of around 0.1 M km2 per decade.  Several reasons for this have been given including, IIRC, reduced surface salinity due to meltwater from the Antarctic ice sheet, and the effects of the ozone hole.

 

Remember, the increase in the Antarctic SIA maximum doesn't have much affect globally because the maximum occurs during the time of least insolation - therefore very little albedo effect.

 

Was there something in particular about Antarctic sea ice you found mind-blowing?

 

You misread my post.

 

I said that the amount of traffic this thread gets in comparison to the Arctic Ice thread is amazing.

 

I posted a link to a recent paper that shows that the current CMIP5 models simulate a decrease in Antarctic Sea Ice Extent when including stratospheric ozone depletion. It's not ozone depletion. It's not known what the cause is.

[PhillipS]

I don't know a lot about #2. The theory sounds plausible. We do know that the Southern Ocean as a whole around Antarctica has been cooling for 30+ years based on satellites which is my personal guess for antarctic sea ice increasing, but maybe that is somehow tied back into land ice melting.

 

The problem is we don't know all that much about the magnitude of land ice melt on Antarctica. There's quite a few studies that produce different results and often the error bars are larger than the magnitude of their results.

 

 

Its an interesting topic though...esp since so much potential sea level rise is locked up in Antarctica. An order of magnitude more than Greenland, so obviously its potential impact is far greater.

 

There is a JPL column on recent Antarctic ice sheet mass loss [source].  here's the graph from that column:

 

Well, I just realized that the column is from 2006 (so much for the "Latest News" headline on it).  Here is a more recent image from NASA:

 

[Snow_Miser]

I think there is some controversy with regard to if the Land Ice is shrinking or expanding. Will (ORH_wxman) posted a link from Zwally et al. that showed that Land Ice Gains exceeded land ice losses. I also posted a few studies backing that up as well.

 

Munneke et al. 2012 published this interesting chart:

 

 

This chart shows the total meltwater volume for various regions in Antarctica on the bottom half of the image, and the total melt on the top part of the image. As you can see, there is no trend in the Meltwater Volume. If anything, it has slightly declined over the last 30 or so years.

 

From the paper:

 

 

"Surface snowmelt is widespread in coastal Antarctica. Satellite-based microwave sensors have been observing melt area and duration for over three decades. However, these observations do not reveal the to

 

A pretty important paper that was just published concerns trends in Antarctic Sea Ice.

 

With Stratospheric Ozone Depletion over Antarctica, and an increase in the concentration of Greenhouse Gases, the CMIP5 models predict an overall decrease in Antarctic Sea Ice. The opposite of what has been observed. Thus, there are factors missing from the models that cause them to incorrectly simulate trends in Antarctic Sea Ice. This paper also refutes claims that stratospheric ozone depletion is responsible for Antarctic Sea Ice increase.

 

http://onlinelibrary.wiley.com/doi/10.1002/grl.50578/abstract

 

From the paper:

 

"The recent observed positive trends in total Antarctic sea ice extent are at odds with the expectation of melting sea ice in a warming world. More problematic yet, climate models indicate that sea ice should decrease around Antarctica in response to both increasing greenhouse gases and stratospheric ozone depletion. The resolution of this puzzle, we suggest, may lie in the large natural variability of the coupled atmosphere–ocean-sea-ice system. Contrasting forced and control integrations from four state-of-the-art models, we show that the observed Antarctic sea ice trend falls well within the distribution of trends arising naturally in the system, and that the forced response in the models is small compared to the natural variability. From this, we conclude that it may prove difficult to attribute the observed trends in total Antarctic sea ice to anthropogenic forcings, although some regional features might be easier to explain."

 

tal volume of meltwater produced on the ice sheet. Here we present an Antarctic melt volume climatology for the period 1979–2010, obtained using a regional climate model equipped with realistic snow physics. We find that mean continent-wide meltwater volume (1979–2010) amounts to 89 Gt y⁻¹ with large interannual variability (σ = 41 Gt y⁻¹). Of this amount, 57 Gt y⁻¹ (64%) is produced on the floating ice shelves extending from the grounded ice sheet, and 71 Gt y⁻¹ in West-Antarctica, including the Antarctic Peninsula. We find no statistically significant trend in either continent-wide or regional meltwater volume for the 31-year period 1979–2010."

 

 

Bump for PhillipS

[PhillipS]

Bump for PhillipS

 

 

I think that you're drawing a distinction without a difference.  The plot I posted showed a 900 - 1000 Gton loss of Antarctic ice over an eight year period - call it 110 - 125 Gton per year of both meltwater and glacial calving.  The paper you linked to says that the Antarctic ice sheet has been losing around 90 - 110 Gton per year due to meltwater alone.  It seems to me that they agree within the uncertainty margins.

 

Please keep in mind that 1 km3 of ice weighs close to 1 gTon so the calving of a single tabular Antarctic iceberg can be many gigatons of ice lost.  Here's a pic of the Pine Island glacier in the process of calving a 900 km2 berg [source]:

 

 

So even if Antarctic ice loss due to direct melting remains constant as your paper predicts, if glacial calving increases the net mass balance would be increasingly negative.

[Snow_Miser]

I think that you're drawing a distinction without a difference.  The plot I posted showed a 900 - 1000 Gton loss of Antarctic ice over an eight year period - call it 110 - 125 Gton per year of both meltwater and glacial calving.  The paper you linked to says that the Antarctic ice sheet has been losing around 90 - 110 Gton per year due to meltwater alone.  It seems to me that they agree within the uncertainty margins.

 

What are you talking about? The paper I linked to shows no statistically significant change in Antarctic melt over the last 30 years.

[PhillipS]

What are you talking about? The paper I linked to shows no statistically significant change in Antarctic melt over the last 30 years.

 

Look at the graph you posted.  The Y-axis is labeled in Gtons/year - that's the values for the annual Antarctic melting.  What the paper is claiming is that there has been no acceleration in melting, and the authors feel that the net melting has declined a bit.  But the paper clearly says that Antarctica is losing 90 to 110 gigatons of ice mass every year.

 

What did you think it meant?

[Snow_Miser]

Look at the graph you posted.  The Y-axis is labeled in Gtons/year - that's the values for the annual Antarctic melting.  What the paper is claiming is that there has been no acceleration in melting, and the authors feel that the net melting has declined a bit.  But the paper clearly says that Antarctica is losing 90 to 110 gigatons of ice mass every year.

 

What did you think it meant?

 

It doesn't say anything about losing 90-110 Gigatons per year.

 

From the Munneke et al. paper:

 

"However, the trend in melt volume, which is the most relevant quantity, can be deduced only from RACMO2 data, and is slightly negative at

0.90 Gt y2 but not statistically significant."

 

[PhillipS]

It doesn't say anything about losing 90-110 Gigatons per year.

 

From the Munneke et al. paper:

 

"However, the trend in melt volume, which is the most relevant quantity, can be deduced only from RACMO2 data, and is slightly negative at

0.90 Gt y2 but not statistically significant."

 

 

The definition of meltwater is "melted snow or ice" [source].  Whether the context is Antarctic ice sheet, Greenland ice sheet, or glaciers, meltwater is liquid, not solid, and it can form ponds or run off along the surface or through moulins.  Granted, some meltwater may refreeze, but the overwhelming majority of meltwater is lost to its source ice mass.

 

The graph that you posted from the Munneke et al 2012 paper gives the annual Antarctic meltwater values as calculated by their model for the period 1979 through 2009.  The highest value they show is 180 Gtons in 1992, and the lowest is 30 Gtons in 2008.  The 90 - 110 Gton range I gave is simply the endpoints of the trendline on the chart you posted.  The authors make it clear that their sensors cannot measure ice loss (meltwater) directly so they relied on a model in their analysis.  But I didn't see any mention that their model was independently verified or validated - or that their model's code is available for independent review.

 

The chart I posted from the GRACE site is the cumulative measured Antarctic ice loss for the period 2003 through 2011.  GRACE actually measures the gravimetric changes in the Antarctic ice sheet - it's empirical data, not model output.

 

In my opinion, actual data and observations (GRACE) have a lot more credibility than output from unverified and unvalidated computer models (Munneke).  Do you agree that data trumps models - or, if not, could you share the reasons for your preference for models over empirical data?