Wednesday, 12 June 2019

The World Meteorological Organisation will build the greatest global climate change network

“Having left a legacy of a changing climate, this [reference climate network] is the very least successive generations can expect from us in order to enable them to more precisely determine how the climate has changed.”

Never trust a headline. The WMO cannot build the network. But the highest body of the World Meteorological Organisation (WMO) has approved our plans for a Global Climate Reference Station Network. Its Congress with the leaders of all member organisations meets every two years in neutral Geneva, Switzerland, and has approved the report on a Global Surface Reference Network of the Global Climate Observing System (GCOS) Task Team on a reference network. The WMO is the oldest international organisation and coordinates the works of its members, mostly national weather services. So the WMO will not build the network itself; we are now looking for volunteers.

(Disclosure: I am a member of the Task Team.* Funny: in a team with big name climatologists I am somehow the "Climate scientist representative".)

Humanity is performing the greatest experiment in its history. We better measure it accurately. For humanity and for science.

Never trust a headline. What the heck does “greatest” mean? As someone trying to estimate how much the climate has changed, I would have been so happy if people had continued the really poor measurement methods they used in the 19th century. Mercury thermometers were placed in the North (pole) facing window of an unheated room. Being so close to the building is not good for ventilation, the sun could get on the sensor or heat the wall beneath. I would have lost that fight. Mercury thermometers are now forbidden. Weather prediction models would be better than this observation. The finance minister would have forced us to switch to automatic measurements. We may think that how we measure today is good enough, but people in 2100 will likely disagree.

At least following the biggest technological steps will be unavoidable. If that happens we will make long comparisons with the old and new set-up; estimating differences in the averages is not enough, also the variability is affected, which is hard to estimate. The reasons for measurement errors will change and thus its dependence on the weather.

Any data processing, if only averaging or applying a calibration factor, that is performed today, will be performed on hardware and software that is not available in 2100. Any instrument we would buy off the shelf will not be available in 2100; the upper air reference network is being forced to change their instruments because Vaisala will soon no longer sell them. So best means that we have open hardware and open software so that we can keep on building the instrument, can redo the data processing from scratch and can recreate the exact same processing on newer computers or whatever we use after the Butlerian Jihad.

Photo of a station of the US Climate Reference Network with a prominent wind shield for the rain gauges.
A station of the US Climate Reference Network.

Never trust a headline. What does measuring climate mean? I work on improving trend estimates based on historical measurements made in many different ways by comparing neighbouring stations with each other (statistical homogenisation). This makes me acutely aware that there is only so much you can do with statistical homogenisation, a considerable error remains. It works relatively well for annual average temperatures because the correlations between stations are high. Much harder are estimates of the changes of the variability around the means, which are important for changes in extreme weather. Especially estimates of changes in precipitation, humidity, insolation, cloud cover, snow depth, etc. have wide confidence intervals because statistical homogenisation is very hard. For these other observations having reference data that does not need to be statistically homogenised is crucial. These other variables are very important for climate change impacts and understanding how the climate is changing. Reference networks can not only help in quantifying these confidence intervals, but as an independent line of evidence also provide confidence the confidence intervals are right.

The preliminary proposal for variables to observe in reference quality is:
  • Air temperature
  • Precipitation
  • Pressure
  • Wind speed and direction (10 m)
  • Relative humidity
  • Surface radiation (down and up)
  • Land Surface Temperature
  • Soil moisture
  • Soil temperature
  • Snow/ice (Snow Water Equivalent)
  • Albedo
If you disagree or have additional ideas please contact us.

Tiered system of systems approach.

Never trust a headline. By itself this network will not be the best to study climate change. We also need the other stations. The reference network will be the stable backbone of the entire climate observation system. The part which is best at estimating the long term trends, while we need the other stations to reduce sampling errors and study spatial patterns.

Maintaining a reference station will be clearly more expensive than a standard climate station. Thus the number of stations will be limited. For the long term warming we expect to need about 200 stations well spread over the world. This takes into account that even if we select locations where we expect nothing will happen in the next century, we will still loose some stations due to conflict or "progress".

At a reference station (or nearby) preferably also measurements with the locally standard set-up are made, so that they can be compared with each other and provide information on any measurement problems. This will improve the quality of the entire network. A network with 200 reference stations would on average have about 1 station per country. For the comparison with the national networks having at least one station per country would also be desirable, but large countries will need multiple stations and it is also more efficient when countries with a reference station have multiple stations because a large part of the costs are overheads (well-trained operators and well-instrumented laboratories).

A society grows great when old men plant trees whose shade they know they will never sit in - Greek proverb (I did not check the provenance, experience tells me, the source of such quotes is always wrong, but do leave a comment).

Never trust a headline. The reference network is not only interesting for studying climate change. If it were we would need to wait many decades before it becomes useful. In this age that would likely mean that it would not be funded. Due to the metrological [sic] standards for computing confidence intervals and the traceability back to SI standards, the measurements will be comparable all over the world within specific confidence intervals for the absolute values, not just the (e.g., temperature) anomalies mostly used to study climate change. Together with the representativeness of the stations for the region this makes the network useful for the validation of absolute estimates from satellites or atmospheric models.

Also the comparison of the reference measurements with the national networks will produce valuable information within the first decade. For example, the American Climate Reference Network shows that the warming estimates of the national network are reliable and if anything underestimates the warming in America; the reference network has the larger trend.

Graph showing the US climate reference network (USCRN) and the normal US network (ClimDiv)
The US Climate Reference Network (USCRN; red line) is below the normal national station network (ClimDiv; green line) in beginning and above it at the end. The trend of the reference network is thus larger. (The values themselves are quite noisy because America is just a small part of the Earth and trends over such short periods do not contain information on long-term warming.)

Never trust a headline. We are land animals and it is thus come natural to us to see climate stations as prototypical for climate observations, but the climate system is much richer. There is already a network for reference upper air measurements (GRUAN) made with weather balloons (radiosondes). The high metrological quality of the ARGO network probably also makes them a reference network. They measure ocean temperature profiles to estimate the ocean heat content.

Both the upper air and the oceans are wonderfully uniform media to measure; characterising the influence of the surroundings and preventing changes therein will be the main additional challenge of a land station network.

Studying climatic changes in urban regions is also important. Here it would be even more important to accurately describe the surrounding because changes will happen. Thus urban regions would need their own reference network.

We hope that our reference network will stimulate the founding of further reference networks. The cryosphere (the part of the Earth which is frozen) needs specialised observations. Hydrological and marine surface observations in reference quality would be very valuable; we should never forget that 70% of the Earth is water. Observations of tiny airborne particles (aerosols) and clouds could be made in reference quality.

In other news. The WMO Congress has also decided to make & share more real-time observations for weather predictions. The norms for quality & quantity will become more strict & are monitored.

20-25% of WMO members is already compliant.

25-30% would be compliant if they would share their data internationally. Many of these countries are big, so they represent a larger part of the world.

The rest will need international support to build the capacity to extend their measurement program and share the data.

Hopefully, the Green Climate Fund can help. The 24/7 monitoring by the WMO will give feedback to the funders on the value of their investment.
Climatology has the advantage that national weather services perform observations operationally. This institutional support has produced the long series we can use to study climate change. We currently see huge changes in the biosphere. Insects seem to be vanishing, but this is really hard to study without long-term observations. The ecological long-term observational programs need institutional support.

Where possible these reference networks should aim to use the same locations, so that the observations can support each other, as well as to reduce costs. It may be easier to obtain funding for reference networks in a large coalition than for every network separately. So I hope that these other communities will develop similar plans. If you know of anyone in these communities, please point them to this post or our report.

We estimate that this reference land station network will cost a few million dollars per year. Thus running this network for a decade would still cost much less than a single satellite missions, which measures far fewer climate variances and has much less accuracy and less confidence in its accuracy. If you know someone at Lockheed Martin or Airbus who may be interested in building a space-grade reference network and has the right lobbyists, please tell them of this initiative.

Coming back the first paragraph: we need volunteers. We need weather services interested in setting up reference stations and we need ones interested in becoming a Lead Centre. A Lead Centre would coordinate the network, organise joint calibrations and comparison campaigns, lead the drawing up of measurement requirements, etc. To spread the work load it could be an idea to one Lead Centre to one instrument or observation type. Please talk about this with your colleagues and spread this post.

* The opinions in the post are mine, the report represents the opinion of the Task Team.

Further reading

Thorne P.W., H.J. Diamond, B. Goodison, S. Harrigan, Z. Hausfather, N.B. Ingleby, P.D. Jones, J.H. Lawrimore, D.H. Lister, A. Merlone, T. Oakley, M. Palecki, T.C. Peterson, M. de Podesta, C. Tassone, V. Venema and K.M. Willett, 2018: Towards a global land surface climate fiducial reference measurements network. Int J Climatol., 38, pp. 2760–2774.

The report of the GCOS Task Team: GCOS Surface Reference Network (GSRN): Justification, requirements, siting and instrumentation options

GCOS, 2017: Report of the 1st Meeting of the GCOS Surface Reference Network (GSRN) Task Team
Maynooth, Ireland, 1-3 November 2017.

My first post trying to get the discussion going in October 2016: A stable global climate reference network

January 2018 GCOS Newsletter on designing a GCOS Surface Reference Network

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