Posted by drj | Filed under Uncategorized
Along with other changes I’ve been making to ccc-gistemp I recently added a feature to remove GHCN stations that are in the contiguous US. I did that partly because GISTEMP’s Fortran has a similar feature, and partly because it allows me to do the following whimsical experiment:
Running ccc-gistemp with no USHCN data and dropping contiguous US stations from GHCN:
tool/run.py -p 'retain_contiguous_US=False;data_sources=ghcn,scar,hohenpeissenberg'
The -p allows a parameter from parameters.py to be set, without editing that file. retain_contiguous_US and data_sources are recently added parameters.
Onto the graphs!
Hmm, not much difference.
What about removing the ocean? Removing it should bring the differences due to land stations into sharper focus:
Tiny differences, not easily distinguishable from rounding.
What about zooming into the Northern Hemisphere, where the US is located?
Aha, some slightly less tiny differences appear which are not due to rounding. US citizens may be interested to note that their contribution to the recent trend is to lower it by a tiny amount (the trend is lower when US stations are included).
ccc-gistemp produces zonal anomaly files (because GISTEMP does). I’ve not really looked at them much before, but we can zoom in further on Zone 24N to 44N where most of the contiguous US is found. Note I had to rescale the next chart to fit the higher peaks in:
What above the next (GISTEMP) zone north, which includes the remaining part of the contiguous US but which has a slightly less dense station network and more volatile temperature swings:
The differences are all lost in the noise?
The US is only about 1½ percent of the Earth’s surface after all.
Posted by drj | Filed under Uncategorized
Over at his blog, Nick Stokes selects rural stations with more than 90 years of data and that report in 2010. In GHCN he counts just 61 stations.
We can do something similar with ccc-gistemp. We get a result that is unreasonably similar to the official GISTEMP with full series.
That major differences in methodology are:
- I use the GISTEMP version of rural, locations with a brightness less than 10 (units of whatever the night-time satellite map is in);
- I count stations after Step 1, which is after USHCN data has been incorporated and multiple records at the same location have been combined;
- GISTEMP analysis algorithm rather than Stokes’.
Here’s the short (but not very clear) Python script that identifies long rural stations:
rural = set((row[:11] for row in open('input/v2.inv') if int(row[102:106]) <= 10)) def id11(x):return x[:11] def id12(x):return x[:12] import itertools rurlong = [group for group,rows in ((g,list(r)) for g,r in itertools.groupby(open('work/v2.step1.out'), id12)) if id11(group) in rural and len(rows) > 90 and rows[-1][12:16] == '2010'] print len(rurlong)
There are 440 stations. With these 12-digit record identifiers in hand it is a trivial matter to create a new v2.mean file («open(‘v2.longrural’, ‘w’).writelines((row for row in open(‘work/v2.step1.out’) if row[:12] in rurlong))» if you must).
As I said before the results are pretty close to the standard analysis:
The new v2.mean file is over 10 times smaller (uncompressed) than the official GHCN v2.mean file. The analysis is correspondingly about 10 times quicker to run (a few minutes on my old laptop). In case you want to use this file, to replicate my results or run it through your own analysis, I’ve made it available from our googlecode repository.
Posted by drj | Filed under Uncategorized
In this comment Bob Koss notices something a little about some of the 1980 anomalies near Byrd station (-80.0-119.4). He points out there is a patch of suspiciously zero anomaly north of Byrd. Illustrated by this graphic (the dot is Byrd, roughly):
Here’s an extract from ccc-gistemp’s Step 3 output (work/v2.step3.out) showing that several cells have flat 0 anomalies for 1980:
-77.2-121.5C1980-9999-9999 0 0 0 0 0 0 0 0 0 0 -77.2-112.5C1980-9999-9999 0 0 0 0 0 0 0 0 0 0 -77.2-103.5C1980-9999-9999 0 0 0 0 0 0 0 0 0 0 -77.2-094.5C1980-9999-9999 0 0 0 0 0 0 0 0 0 0 -74.8-130.5C1980-9999-9999 0 0 0 0 0 0 0 0 0 0 -74.8-121.5C1980-9999-9999 0 0 0 0 0 0 0 0 0 0 -74.8-112.5C1980-9999-9999 0 0 0 0 0 0 0 0 0 0 -74.8-103.5C1980-9999-9999 0 0 0 0 0 0 0 0 0 0 -74.8-094.5C1980-9999-9999 0 0 0 0 0 0 0 0 0 0 -72.7-139.5C1980-9999-9999 0 0 0 0 0 0 0 0 0 0 -72.7-130.5C1980-9999-9999 0 0 0 0 0 0 0 0 0 0 -72.7-121.5C1980-9999-9999 0 0 0 0 0 0 0 0 0 0 -72.7-112.5C1980-9999-9999 0 0 0 0 0 0 0 0 0 0 -72.7-103.5C1980-9999-9999 0 0 0 0 0 0 0 0 0 0 -70.9-139.5C1980-9999-9999 0 0 0 0 0 0 0 0 0 0 -70.9-130.5C1980-9999-9999 0 0 0 0 0 0 0 0 0 0 -70.9-121.5C1980-9999-9999 0 0 0 0 0 0 0 0 0 0 -70.9-112.5C1980-9999-9999 0 0 0 0 0 0 0 0 0 0 -70.9-103.5C1980-9999-9999 0 0 0 0 0 0 0 0 0 0 -69.2-121.5C1980-9999-9999 0 0 0 0 0 0 0 0 0 0
(this file is a v2.mean style file where the 11-digit station identifiers are in fact the centre of the grid cell rounded to the nearest .1 degree in latitude and longitude.)
It turns out that all of those cells have a time series starting in 1980. And this leads to me having to explain a curiosity in the algorithm used to produce anomalies.
The anomalies produce by the gridding step, Step 3, have a baseline of 1951 to 1980 (see gridding_reference_period in parameters.py). What this means is that just before the end of Step 3 each cell’s time series is adjusted: For each of the 12 months in the year, an average is computed for the period 1951 to 1980 and this average is subtracted from that month’s time series.
If there is a cell that is unlucky enough to have its series start in 1980, then the average for the period 1951 to 1980 is simply the 1980 value. That’s subtracted from the series, so after Step 3 all the anomalies for 1980 will be 0 (see list above).
This doesn’t happen a lot. Recall that the GISTEMP analysis uses a grid with 8000 cells. We can see that the vast majority of the cells (that have any series at all) have 30 years of data for the period 1951 to 1980:
(The chart above represents a simplification, but a reasonable one: A year is marked as “present” if it has any valid monthly data)
The vast majority of the cells have a full 30 years for the base period.
What if there are no values between 1951 and 1980? Then in that case the algorithm uses an average over the entire series for its baseline. There are 39 such cells (that’s the tiny blip on the left of the graph).
So some cells will have a different baseline, some cells will have a pathetically small number of values to average over in the baseline (the 1980 example above is the extreme example). This is unfortunate if you’re the sort of person that worries about individual years in localised regions, but it doesn’t affect the larger scale averages at all.
Koss also asks why the cell just north and west of Byrd does not have a yearly anomaly for 1980. A reasonable question since it’s close to Byrd and Byrd has data for 1980.
Here’s a Google Earth screenshot, showing stations south of -70. Taken from roughly above the South Pole with 0 degrees longitude to the right.
Note that this shows stations after Step 2 (I ran the command «tool/kml.py --lat -90,-70 work/v2.step2.out > step2.kml»), and Step 2 discards all stations with a short series, which means throwing out several Antarctic stations.
For the cells (with locations of the form -NN.N-EEE.E), the 4 digit number is the first year with data (technically, the first year with enough data to produce a yearly anomaly, but that’s the same in these cases).
So why does cell -77.2-121.5 (just north of Byrd) have a series that starts in 1980? Answer: Because it uses data from Byrd, and Byrd’s data starts in 1980. The little squiggle inside the icon is the yearly anomaly series and you can just about see that -77.2-121.5 is the same squiggle as Byrd.
What about cell -77.2-130.5 (just north and west of Byrd)? Why does that have no anomaly for 1980? Because its series starts in 1985. Why is that? Because this cell uses data from Gill and not Byrd (again, compare the squiggle to Gill’s squiggle). Why is that? Because there are 3 stations within 1200 km of this cell. I recently added a bit of logging to Step 3 and it’s now possible to see for each cell what stations contributed and the weights of their contribution:
$ grep -e -77.2-130.5C log/step3.log -77.2-130.5C stations [('700893760009', 0.10965896795479568), ('700893240009', 0.0), ('700891250000', 0.0)]
70089376000, Gill, -80.00-178.60
70089324000, Byrd, -80.00-119.40
70089125000, Byrd Station, -80.02-119.53
Byrd and Byrd Station are presumably different stations in more or less the same location. Byrd Station has a temperature record starting in 1957 (yay for International Geophysical Year) running continuously up to 1971, and then sporadic southern summers up to 1987. Byrd is presumably the modern station; its record starts in 1980 and runs up to 2010 (not quite continuously).
When considering the order in which to combine stations to produce a series for a cell, stations are considered “longest record first” by a simple count of the total number of months of valid data. It turns out that Gill, 70089376000, has 246 months of data, while Byrd, 70089324000, has 216 months of data. So Gill comes first (even though Byrd is much closer).
Referring back to the log output for the three stations, we see that records 700893240009 and 700891250000 contributed with 0.0 weight. In other words, not at all. Why is that?
In order for a station to combine with a cell series it has to have a certain number of years of common overlap: parameters.gridding_min_overlap. This is normally 20. Each month of the year is considered separately; it turns out that February is the month for which Gill and Byrd have the greatest overlap, with 18 years in common. Just falling short of the cut. If both Gill and Byrd continue to have temperature records then in 2012 their February record will be combined. This still won’t be enough to compute a yearly anomaly for 1980 for that cell, because only February will combine, not the other months of the year. And one month is not enough to compute a yearly anomaly.
For completeness we should consider Byrd Station, 70089125000, as well. Gill starts in 1985, and Byrd Station has only 4 monthly values since 1985 (and in fact, only 8 for the whole of the 1980′s). So no chance of enough overlap.
However for the cell containing Byrd itself, -80.1-121.5, we can see that its record starts in 1957. Again grepping station contributors out of the log:
$ grep -e -80.1-121.5 log/step3.log -80.1-121.5C stations [('700890090008', 0.079848008479036836), ('700893760009', 0.12098360649264683), ('700893240009', 0.9657843990261038), ('700891250000', 0.96815637481310624)]
The first station is Amundsen–Scott, 70089009000, with a record that starts in 1957 (International Geophysical Year again). We have increased overlap, and so it turns out that Gill and both records from Byrd contribute. You can think of Amundsen-Scott as being like a catalyst that allows Gill and Byrd to combine when they ordinarily would not. Amundsen-Scott is only just within range to contribute to this cell. Cells further north will not use Amundsen-Scott, so Gill and Byrd will not combine (unless there is some other station in range to provide an overlapping series).
Conclusion: Some individual cells can have slightly unintuitive series, but they are merely the result of the documented computation (the key facts—that records are combined longest first, stations from up to 1200 km away are used, and records require an overlap for combining—are all documented in Hansen and Lebedeff 1987). A tiny fraction of cells in the anomaly maps either have misleadingly short anomaly periods or entirely different anomaly periods. This makes no difference to zonal averages. Probably when browsing the maps such cells should be marked or eliminated.
Posted by drj | Filed under announcement
I am pleased to announce ccc-gistemp 0.5.1 (the astute reader will note that there is no announcement for release 0.5.0. It is available but does not work in Python 2.5.1 so I fixed that for release 0.5.1).
Compared to the previous release, the changes are not so grand. This release incorporates many incremental improvements to clarity. It also has a couple of bug fixes: to cope with the fact that the GISTEMP source tarfile that we used changed its layout (see this comment here for example); and to once again run on Python 2.4 (a thoroughly ancient version, please try and use Python 2.6).
David Jones, Nick Barnes, and Ronan Lamy have contributed to this release.
Posted by Nick.Barnes | Filed under Uncategorized
Updated: I have now 2010-06-29 submitted this comment to the IAC. Thank you, all signatories.
We have a rare opportunity to affect the conduct and perception of climate science. If you believe this is important, please read on, and comment.
The Intergovernmental Panel on Climate Change (IPCC) produces reports which review and summarize the science of climate change. These reports are then used by inter-governmental treaties, bodies, conferences, and national governments, as the basis for international and national policies on climate change. In other words, it is vitally important. The Clear Climate Code project has the goal of “increasing public confidence in climate science results”, and the perception of IPCC reports directly affects this goal.
There has been a lot of controversy about the accuracy and balance of IPCC reports. In response, in March the UN asked the InterAcademy Council (representing the national science academies of many different countries) to conduct a review of the IPCC processes and procedures. A committee has been established and the review is underway. The committee is now soliciting public comment. This is a rare opportunity to influence the way in which the science of climate change is conducted, reviewed, synthesized, and communicated.
I have written the following comment, and am hereby soliciting signatures. If you agree with this comment and would like to be added as a signatory, please either contact me directly, or post a comment to this blog post, giving your name and affiliation, as you wish it to appear in the list of signatories. Please also spread the word about this blog post, and encourage your friends, colleagues, and contacts to sign it.
[edited to add: as people send me their endorsements, I will update the list of signatories here in the post. I cannot make other changes, since this is now receiving signatures.]
Comment to the InterAcademy Council Review of the Intergovernmental Panel on Climate Change.
The IPCC procedures should be amended to increase the transparency of
the science and of the IPCC process itself. The proposed amendments
are small, but would have a large effect on confidence in IPCC
“Sunlight is said to be the best of disinfectants” – Louis D. Brandeis, 1913.
2. The Problem
IPCC reports contribute to global public policy debates and processes,
which may have major effects on the daily lives of every person in the
world. Every government and large enterprise has already been
affected. As the century continues, the effects of policies based on
IPCC work will increase in their scope and impact: they will create
whole new industrial sectors, thousands of businesses, and many ways
For this reason, the IPCC reports and the processes which create them
have been under increasing scrutiny. Questions are asked and doubts
are raised, both about the IPCC process and about the underlying
scientific research. Both the research, and the processes of review
and synthesis, have been criticised for opacity. Very serious
accusations have been made: of a lack of rigor, of group-think, of
conflicts of interest, of deception, and even of conspiracy and fraud.
This has led to doubts about the validity of IPCC conclusions, and to
serious difficulty in making national and international policy
regarding climate change.
All this is well-known and need not be rehearsed further here.
Indeed, the recognition of these problems has led directly to the
United Nations request for a review, and the establishment of this IAC
3. The Solution
A key part of any solution to these problems is to increase the
transparency of the research underlying IPCC reports, and of the IPCC
process itself. While the research and the process remain closed and
opaque to commentators and to the public, doubts will flourish and
will impede progress.
The IPCC AR4 WG1 report included references to around 5000 items of
peer-reviewed research. Thousands more were referred by the WG2 and
WG3 reports. To assess or fully understand any part of an IPCC
report, an interested reader will want to follow the bibliographic
references and read the underlying research. For this reason the
bibliographic function of an IPCC report is very important. However,
the IPCC AR4 bibliography does not perform it well.
Each chapter of each report of AR4 has its own separate bibliography.
These bibliographies are not linked together, within a report or
between reports. The formats of these bibliographies varies. There
is no way to see whether any given paper is referred in more than one
working-group report, in more than one chapter, or at all. In the
online published text of each chapter of AR4 each citation does not
link to the matching reference in that chapter’s bibliography. In
turn, in each chapter’s bibliography, each reference does not link to
any online materials relating to that piece of research.
AR5 should have a single unified bibliography, containing all
references in all working group reports. Each citation in the body of
a report should link to the matching entry in the bibliography. If a
reference is to material which is published online, the bibliography
should link to that publication. The bibliography should also
reproduce whatever part of the publication and supporting materials is
available for reproduction (possibly just the abstract, but see
below). To protect these references against future change or loss,
wherever possible the IPCC should also archive copies of any online
publication on its own server (for instance, at the IPCC Data
Distribution Centre http://www.ipcc-data.org/).
There are many free tools available for managing online bibliographic
databases and repositories such as this. Such tools allow
collaborative enterprises such as the IPCC to readily create,
populate, update, search, and publish bibliographic data. The IPCC
should adopt such a tool, and mandate its use by lead authors and
contributing lead authors.
3.2. Underlying Research
Each piece of research lies somewhere on a spectrum of transparency
and open-ness. Some publications are open-access: freely available
for anyone to read and assess. For instance, some are published in
open-access journals. Many are not open-access, but describe results
such as datasets which are publicly available. Still more may have
some additional materials, such as computer source code used to
produce or analyse the datssets, freely available for download.
Finally, a great deal of research is entirely closed: only the
abstract is available, and neither the scientific paper, nor the data
described in the paper, nor the computer source code (or other
processing details), is generally open.
In recent years, and especially since AR4, it has become clear that
public confidence in research is directly connected to this spectrum
of transparency. The more open the research, the less vulnerable it
is to criticism, and especially to the more serious accusations of
fabrication and fraud. As argued above, this criticism seriously
damages the reputation of the IPCC and impedes progress in the use of
the IPCC reports.
For this reason, all contributors to AR5 should be encouraged to open
their work as much as possible: to make their contributed papers
available online, to publish their datasets and supporting materials
such as computer source code, design documents, and additional text,
images, and charts. This can be very simply done by the IPCC
routinely gathering and publishing information about the transparency
of each piece of underlying research. This information can easily be
stored in the IPCC bibliographic database.
As noted above, whenever possible a publication, and/or supporting
material, should be copied to an IPCC repository, to protect against
change or loss. As publications in climate science become more open,
such reproduction should be increasingly possible.
3.3. The IPCC Process
Much of the IPCC process itself is already open. Draft reports,
review comments, and responses are all published. However, the IPCC
reports themselves are not open. It is not possible to freely
reproduce and disseminate them. The IPCC should immediately change
this, and adopt an open licensing policy. All IPCC reports, past and
future, should be freely available under a license which conforms to
the Open Knowledge Definition http://www.opendefinition.org/, for
example the Creative Commons Attribution Share-Alike license CC-BY-SA http://www.opendefinition.org/licenses/cc-by-sa/.
The existing transparency should also be increased. There have been
prominent recent calls for the review and synthesis process to take
place in public, for instance by adopting a wiki-style drafting
mechanism. Such a move would protect the IPCC against certain
accusations of group-think (or even conspiracy). However, such a move
is somewhat outside the scope of the detailed recommendations below.
This is a series of concrete recommendations for amendments to the
document “Principles Governing IPCC Work, Appendix A – Procedures for
the preparation, review, acceptance, adoption, approval and
publication of IPCC Reports”, with the effect of implementing the
solutions described above.
In section 4.1, “Introduction to Review Process”, this paragraph should
The IPCC Secretariat should identify, implement, and provide a
bibliographic system and repository for the use of Coordinating
Lead Authors, Lead Authors, and Review Editors.
The content of this bibliographic system and repository shall be
shared between all the Working Groups and the Task Force on
National Greenhouse Gas Inventories, and shall be publicly
available on or before completion of the Report for a period of at
least five years.
In section 4.2.3, “Preparation of Draft Report”, this sentence should
be added to the first paragraph:
Contributions should include, wherever possible, access
instructions for any original data, supplementary materials,
computer source code used for analysis or processing, and an
indication of the public availability and licensing of such
In Annex 1, under “Lead Authors”, this paragraph should be added:
Lead Authors shall record all contributed material in the IPCC
bibliographic system. Where any access to original data,
supplementary materials, or computer source code is provided, Lead
Authors shall record such access in the IPCC bibliographic system
and, wherever possible, copy such material to the IPCC repository.
In section 4.2, “Reports Accepted by Working Groups and Reports
prepared by the Task Force on National Greenhouse Gas Inventories”,
this paragraph should be added:
Reports accepted by Working Groups, or prepared by the Task Force
on National Greenhouse Gas Inventories, shall be made publicly
available under the Creative Commons Attribution Share-Alike
In section 4.4, “Reports Approved and/or Adopted by the Panel”, this
paragraph should be added:
The Synthesis Report shall be made publicly available under the
Creative Commons Attribution Share-Alike license CC-BY-SA.
Furthermore, the IPCC should make its existing reports publicly available
under the same CC-BY-SA license.
The IPCC reports have been questioned and attacked on many fronts, and
this has been a source of great difficulty in making national and
international policy regarding climate change. A principal ground for
complaint has been the transparency of the underlying science and of
the IPCC process of review and synthesis. Progress can be enabled by
addressing these complaints: by making the science and the process far
The IPCC doesn’t have a direct influence on the working practices of
the thousands of researchers who contribute work to its reports.
However, it can shine a bright light on those practices by the simple
and cheap step of requesting and recording certain information in its
bibliography, and by making that bibliography readily available to the
Finally, by making its own processes more open, and by making its own
reports more freely available, the IPCC can both avoid any further
criticism on these grounds and set a leading example for the research
community from which it is drawn.
- Nicholas Barnes, Founder, Clear Climate Code project
- David Jones, Founder, Open Climate Code project
- Richard Drake, Founder, Open Climate Initiative
- Rufus Pollock, Founder, Open Knowledge Foundation
- Jonathan Gray, Community Coordinator, Open Knowledge Foundation
- Joshua Halpern, Professor of Chemistry, Howard University
- Tim Lambert, School of Computer Science and Engineering, University of New South Wales
- Peter Murray-Rust, University of Cambridge and Open Knowledge Foundation
- Andrew Montford. Author: The Hockey Stick Illusion
- Subbiah Arunachalam, Distinguished Fellow, Centre for Internet and Society, Bangalore, India
- Dave Berry, ex Deputy Director of the UK National e-Science Centre
- Peter Suber, Berkman Fellow, Harvard University
- Lucia Liljegren of the Blackboard
- Carrick Talmadge, Senior Scientist, University of Mississippi
- Ivo Grigorov (Centre National de la Recherche Scientifique/DTU-Aqua)
- William Eichinger, William Ashton Professor of Engineering, University of Iowa
- Nick Levine
- Philippa Davey
- Leif Burrough
- David L. Hagen
- Scott McKay
- Ronald Broberg
- Ted Lemon
- Martin Brumby
- Gerry Morrow
- David Bishop
- Conrad Taylor
- John Shade
- Allen McMahon
- Robert Thomson
- Eamon Watters
- Bruce Cunningham
- Greg Freemyer
- Chad Herman
- Barry Woods
- Jack Mosevich
- Stephen L. Jones
- Zeke Hausfather
- Daniel Godet
- Laurence Childs
- Peter O’Neil
- Phillip Bratby
- Colin Brooks
- Andrew Smith
- Peter Walsh
- Louis Hooffstetter
- Steve Fitzpatrick
- Stephen Gaalema
- Charles Minning
- Brian Crounse
Posted by drj | Filed under Uncategorized
More or less on a whim I split the GHCN data into two sets: Those stations marked as being at an airport; those stations not marked as being at an airport. This is easy to do because the v2.inv file puts an ‘A’ in column 81 (counting from 0) for airport stations.
Here’s the airport versus non-airport comparison for ccc-gistemp:
Certainly for the most recent 50 years it doesn’t seem to matter much whether you use exclusively airport based measurements or exclude airport based measurements (considering the global anomaly).
My earlier post about the 1990s station “dropout” used a similar technique of splitting the input data into two sets.
Posted by drj | Filed under Uncategorized
Saturday past was OKCon 2010 and we were in London to give a presentation about Clear Climate Code (well, Nick, Paul, and I were). Specifically, I was there to monkey the slides, and Nick was there to stand up and talk.
It was an interesting conference; thanks to Open Knowledge Foundation for organising, and everyone else for attending.
Posted by drj | Filed under status
tool/vischeck.py has been recently updated so that it computes and draws trends (the work was done by me and Nick Barnes). Here’s some recent comparisons redrawn with trends:
The “before 1992 / after 1992 stations” from “The 1990s station dropout does not have a warming effect”:
The short trends are done with the last 30 years of data for each series (which since one series ends in 1991, is a different period for each). Notice how similar the recent trends are.
Reprising the Urban Adjustment post:
I don’t think I’ve done a combined land and ocean chart comparing hemispheres for the blog before, but here it is now:
Nick Barnes added the calculation of R2 whilst I was writing this post, causing me to redraw all the charts.
Nick has also been exploiting ccc-gistemp‘s new parameters.py module, and did a run with the somewhat experimental 250km smoothing rather than the traditional 1200km smoothing. The parameter is named gridding_radius and it affects gridding in Step 3; setting it to 250km essentially reduces each station’s influence to very roughly the size of the cell used in gridding.
The effect on the trends is most visible in the Northern Hemisphere:
Trends are just one minor example of the way in which the ccc-gistemp code can be continuously improved. We don’t just draw trends for one graph, we improve the code so that all graphs can have trends.
Posted by Nick.Barnes | Filed under announcement
[Updated: ccc-gistemp release 0.4.1 is now available]
I am pleased to announce ccc-gistemp release 0.4.0. This release is much clearer than previous releases. Give it a go.
- Almost all of our code has now been rewritten to remove the Fortran style which remained from the original conversion from GISTEMP. Previous releases had greatly improved steps 0-2; this release continues the improvement work there and also carries those improvements through steps 3-5. Almost all of the code now has sensible variable and function names, clearer data handling, and helpful comments. Many unused variables and functions have been removed. The current core algorithm has 3740 lines of code, of which more than half are either comments, documentation strings, or blank.
- Rounding has been completely eliminated from the system. Previously, rounding and truncation code was used to exactly emulate GISTEMP. Rounding made the code less clear, and Dr Reto Ruedy of NASA GISS confirmed that rounding was not important to the algorithm, so it has been removed. All temperature data is now handled internally as floating point degrees Celsius (previously it was a mixture of integer tenths, floating point tenths, and floating point degrees) and all location information is handled as floating point degrees latitude and longitude (previously it was a mixture of floating point degrees and integer hundredths).
- In a normal run of ccc-gistemp, no data passes through intermediate files. Much of GISTEMP is concerned with generating and consuming intermediate files, to separate phases and to avoid keeping the whole dataset in memory at once (an important consideration when GISTEMP was originally written). We have now completely replaced this with an in-memory pipeline, which is clearer, automatically pipelines all the processing where possible, and avoids all code concerned with serialization and deserialization.
We now have separate code to generate data files between the distinct steps of the GISTEMP algorithm, and to allow running a step from a data file instead of in a pipeline. This allows the running of single steps, and is useful for testing purposes.
- Parameters, such as the 1200 km radius used when gridding, and the number, 3, of rural stations required to adjust an urban station, which were scattered throughout the code, are now all to be found, with explanatory comments, in code/parameters.py
- It’s now possible to omit Step 4 and produce a land-only index, which closely matches GISTEMP.
- It’s also possible to omit Step 2, and run the algorithm without the urban heat-island adjustment.
- GISTEMP recently switched to using nighttime brightness to determine urban/rural stations. We made the corresponding change, which is switchable.
Note that none of these changes altered any of our results by more than 0.01 degrees C, except for the change to urban station identification, for which the changes in our results (none greater than 0.03 degrees C) closely match the changes the GISTEMP results.
The work for this release has been done by David Jones, Paul Ollis, and Nick Barnes.
Posted by drj | Filed under announcement
As I pointed out in an earlier article ccc-gistemp can now create a land index by omitting Step 4: python tool/run.py -s0-3,5.
Here’s how we compare with official GISTEMP: