How to Measure Temperature in the Arctic — the Lesser of Two Evils

Danish Meteorological Institute scientists Michael Heeris, left, and Villy Dohrmann measure temperature on the summit of the Greenland ice cap. GISS scientists are seldom pictured in the field.

As has been well covered by Steve Goddard on WUWT, the “interpretation” of Arctic conditions by NASA/GISS is based on astonishingly little data north of 80 degrees latitude, which is to say no data at all.

As the Danish Meteorological Institute (DMI) has been offered as a source of actual data and information, rather than imaginary data and imaginary information, and as the word “model” has been bandied around on WUWT as a problematic aspect of DMI’s temperature product, I thought now might be a good time to share an e-mail exchange I had several months ago with the DMI’s Gorm Dybkjær. Below is a lightly edited version of our exchange. Many of Dybkjær’s statements are very interesting.

Dear DMI:

I am an American journalist completing a book about climate change and have been studying your Arctic temperature graph for some time. The graph says that the data are obtained by the use of a model.

I wonder if you can tell me how many temperature stations the average represents, and why the word model is used. (I would anticipate the word ”model” to be a predictive computer analysis, as opposed to descriptive.)

Would it be possible to clear this up?

Thank you in advance.

Sincerely yours,

Harold Ambler

To which Dybkjær responded:

Dear Harold

Concerning your question about the number of in situ temperature observations (direct measurements) there is available in the Arctic – the brief answer is – there are not many! My guess is that the number of buoys in the Arctic Ocean that provide near-real-time temperature observations for e.g. numerical weather prediction (NWP) models are around 50. The number of land based weather stations on the rim of the Arctic Ocean are probably even less. You must contact WMO (world meteorological organization) for more accurate numbers.  So by dividing the area that the ‘mean temperature’ graph represents by 100 temperature observations, you will of course find that each observation must represent an enormous area. That is exactly why you want to use NWP models to estimate distributed temperatures in the Arctic.

The NWP models used for the ‘mean plus 80N temperature’-graph on ocean.dmi.dk are, as you mention, a predictive numerical model. However, before you let the model ‘go’ to do the weather forecast calculations, you must estimate the initial state of the atmosphere. The initial state of the atmosphere is the best guess, based of all observation you have available and the coupled physical constrains of the model. The approximately 100 in situ surface temperature observations is only a very limited part of ‘all available observations’ you feed into the model. You have measurements from airplanes, atmospheric profiling instruments mounted on balloons and then of course the far most valuable input to NWP models today – a huge amount of observations from satellite.

From these data sources all kinds of atmospheric variables are measured/estimated and assimilated into the NWP models. From a ‘bargain’ between the coupled model physics and all the applied observations the model calculates the best initial state of the entire atmosphere. That initial state – the model analysis – is the best guess of e.g. distributed surface temperatures in the Arctic you get.

Hope you can use this clarification.

Best Regards

Gorm /Center for Ocean and Ice, DMI

I found Dybkjær’s response helpful and also confusing. Below are follow-up questions I sent him paired with his responses:

Hi Gorm,

Thank you for your response.

I think I am understanding you somewhat and have a few follow-up questions:

1. Does DMI’s ‘mean plus 80N temperature’-graph use measurements from airplanes?

All available observations, including measurements from airplanes, are used by the models to calculate the best guess of the atmospheric condition. This ‘best guess’ (or ‘analysis’) is calculated 4 times per day of which the 00z and 12z are the basis for the ‘plus 80North’ temperature graph. I must recommend you to contact “European Centre for Medium-Range Weather Forecasts” (ecmwf.int) for details on the amount of observation they use for any of their model analysis.

2. Do you use measurements from satelllites?

Dybkjær: A huge amount of satellite data are also used to produce the ‘best guess’… (see above)

3. Do you use measurements from balloons?

see above

4. Does the number of data-sources change on a daily basis?

Yes – but I do not believe this has a significant effect on the day to day quality. Contact the ECMWF!

5. Do you adjust for this?

No

6. If you do use the sources listed in 1-3, who provides you with the data?

At DMI we get most of our ground based measurements through the WMO – satellite data we either retrieve our selves or get them through various data networks. I guess the same is the case at ECMWF, who run the models used for the temperature graph we are talking about here – so for more details on this please contact ECMWF.

7. Some of the spikes in the record look extraordinarily sharp, and I had previously understood such moments to be cases where sub-polar air overran the Arctic basin. But I wonder if, to some extent, they represent the model over-reacting to a single spike in data from just a few sources? For instance, when I eyeball the temperatures around the Arctic basin, they don’t in every case appear to correspond to the spikes on your graph?

I believe – in general terms – that the spikes of the graph are realistic, but to discuss this further we have to look at specific cases. As I mentioned in an earlier mail, the ‘plus 80 North mean temperature’-values are the mean of all model grid points in a regular 0.5 degree grid – meaning that along each half degree parallel North of 82N, you have 720 temperature values! That means that the ‘plus 80 North mean temperature’ is strongly bias towards the temperatures in the very central arctic and therefore less affected by temperatures along the rim of the Arctic Ocean. Therefore – You can use all the plotted ‘plus 80 North mean temperature’ graphs to compare one year to another or the climate line and you should NOT compare the mean temperatures to a specific temperature measurement.

8. The word model is still confounding here: Basically, the graph represents initial conditions for you to run the model predictions. But the initial conditions are not generated by the model. They are generated by you and the staff at DMI, correct?

The initial conditions are generated by the model using state-of-the-art atmosphere physical knowledge.

Although our interchange left some questions unanswered, I had learned what I wanted to by this point: DMI’s data for the topmost portion of the globe, north of 80 degrees latitude, while a hodge-podge, and plagued with its own set of issues, was far, far more reality-based than the Arctic data published by NASA/GISS and, thus, the lesser of two evils. I will be in the Sierras and away from my computer for the next 10 days.

Advertisements

About Harold Ambler

I am a lifelong environmentalist. I started my journalism career at The New Yorker, where I worked as a copy editor. Since then, my own work has appeared in The New York Daily News, The National Review Online, The Atlantic Wire, The Huffington Post, The Berkeley Daily Planet, The Providence Journal, Brown Alumni Monthly, The Narragansett Times, Rhode Island Monthly, and Providence Business News.
This entry was posted in Arctic, Climate change, crying wolf, global cooling, global warming, weather and tagged , , , , , . Bookmark the permalink.

4 Responses to How to Measure Temperature in the Arctic — the Lesser of Two Evils

  1. Anthony Watts says:

    Great post, factually enlightening.

    Thanks for your invitation to repost at WUWT.

  2. Harold Ambler says:

    Thanks Anthony. Nice hearing from you on Talking About the Weather. How’s the summer weather been in Chico?

  3. HaroldW says:

    Harold,
    Thanks very much for all the detail about the DMI’s information gathering and analysis methods.

    I posted the following comment at WUWT, but got no response. It may be a poor question, but I’m still wondering about this:

    I’m curious about the statement that the DMI index is the “mean of all model grid points in a regular 0.5 degree grid.” As Dr. Dybkjaer indicates, because of the convergence of longitude lines near the pole, the density of gridpoints increases as one nears the pole, and this biases the index towards the temperature near the pole, as opposed to representing a true regional average.

    Perhaps you could ask a followup question concerning the reason why DMI prefers to form its index using this method, as opposed to an area-weighted average.

    [I think most, if not all, other temperature indices are computed on an area-weighted basis.]

    In posting this, I thought of a few additional questions/comments for Dr. Dybkjaer:
    1. Is it possible to use the DMI archive data to compute a baseline, and produce a temperature anomaly map for the Arctic region? I would think that this would be of sufficient quality that it could be easily incorporated into (say) the HadCRU global temperature estimate, improving its coverage.

    2. The ice extent graph at http://ocean.dmi.dk/arctic/icecover.uk.php conveniently displays traces for the past few years, as well as the long-term average, to facilitate comparison. This is an excellent feature, and I wonder if this could also be applied to the Arctic mean temperature graph at http://ocean.dmi.dk/arctic/meant80n.uk.php . [Or perhaps the additional information just clutters the graph and renders it less helpful.]

    3. The graph of Arctic sea ice minimum extent trend at http://ocean.dmi.dk/arctic/icecover_30y.uk.php is based on NSIDC data. Obviously the metric used in the NSIDC data is not the same as the Arctic sea ice extent metric which DMI produce and display in http://ocean.dmi.dk/arctic/icecover.uk.php . [E.g. NSIDC minimum in 2007 was around 4 M km^2; DMI minimum was around 3M km^2.] What are the significant differences between the two metrics? How do the two trends compare?

    • Harold Ambler says:

      Buried in book publication details now but have recommended to HaroldW to contact Dybkjaer directly (and provided e-mail for same).

Comments are closed.