Probative value thanks to the diversity of sources: Undeniable Evidence of Climate Change

Global temperatures should rise two degrees at most. Science and administration are working toward that goal with great urgency. A wide range of diligently interpreted climate and environmental data provide the foundation for their work.

Text: Elsbeth Flüeler

Seven folders in rainbow colours that go from blue to green and yellow to red sit next to Regine Röthlisberger’s desk. The Deputy Head of the Climate Reporting and Adaptation Section says: “This is the ‘cookbook’ we use to measure Switzerland’s greenhouse gas inventory.” The result is 80 pages full of figures every year. Plus, there is a 500-page handbook with comments on the figures. The first of three parts of the IPCC report has 1,500 pages and weighs 4.2 kilograms. The fifth edition of the scientific work of the Intergovernmental Panel on Climate Change (IPCC) was published in 2013 and conveys the physics principles of climate change.

Certain industrial nations agreed on binding reduction targets for greenhouse gases under the Kyoto Protocol in 1997. Since then, the Parties to the Protocol have been working to develop multifaceted and precise data that represent their greenhouse gas emissions so that they can introduce specific national reduction measures. As for scientists, they are doing everything they can to issue clear statements on climate change to policy-makers. The last IPCC report included scientific articles about climate issues from a total of 254 authors. Stefan Brönnimann, who leads the Climatology Group at the Institute of Geography of the University of Bern, was one of them. He co-wrote with 14 other authors the report’s chapter on observed atmospheric change.

Certain uncertainties

It is more than certain that the global mean temperature has risen. But what does “certain” mean, the authors asked. And how much uncertainty is there in this scientific claim? According to the authors, a finding is really only certain if different types of proof lead to the same conclusion independently from one another. Or in the language of the IPCC report: If there are “multiple independent lines of evidence”.

Researchers uncovered the first lines of evidence for the changing world mean temperature in the temperature readings taken at the some 30,000 meteorological stations around the world. “In Switzerland”, says Stefan Brönnimann,“we were able to rely on a 150-year tradition of the Swiss Meteorological Institute (SMA) weather stations.” However, while the stations were located at the edges of cities when the measurements began, they gradually ended up in the middle of cities or were relocated to airports; the measurement equipment was replaced by new models - and not only in Switzerland, but everywhere where climate data are collected using state-of-the-art research methods. In the past, critics have complained that these changes influenced temperature trend information and created uncertainty.

So Stefan Brönnimann and his colleagues at the climate centres analysed the raw data in view of these changes and made corrections. “Every correction harbours more uncertainties”, says the climate expert. However, scientists have been working intensively in recent years on the uncertainties involved in the series of measurements. And it turns out that although the corrections were made independently by scientists, the series of measurements proved to be virtually identical for the most part. “The uncertainties can now be better defined, although it may sometimes seem as if general uncertainty has grown.”

Measurements from various independent systems

In addition to ground temperatures, surface water temperatures in oceans provide a second line of evidence according to an independent monitoring system. The series of measurements on surface water temperatures go way back and raise specific uncertainties. In fact, temperatures used to be mainly measured by ships, with boilers until the 1940s and then engine cooling water.

A third line of evidence came from measuring air temperature - also by ships - and a fourth line of evidence came from determining the temperature of the free atmosphere, measured first with weather balloons and later with satellites. But scientists were still on the lookout for other evidence of warming. They analysed glacier volumes, the spread of artic ice, the sea level, the thickness of the snow cover in winter, the general humidity in the air and the heat stored by the ocean.

The result was 11 measurement categories with a total of 44 processed, interpolated and homogenised data sets that all delivered robust scientific evidence of the change in the Earth’s temperature and dispelled specific uncertainties. “The finding”, says Stefan Brönnimann, “is a good example of how multiple independent lines of evidence can lead to a politically relevant scientific claim.” Despite the uncertainties, the finding was the same in all 11 measurement categories: The climate system is clearly warming.

Greenhouse gases: awareness and its political consequences

The IPCC will use this finding to guide policy-makers as they develop subsequent policy instruments to the Kyoto Protocol. Switzerland will return once again to the negotiating table and decide on climate protection targets. Parliament is now discussing the ratification of the second commitment period under the Kyoto Protocol and the commitment to reduce greenhouse gases by 20 percent from their 1990 levels. The measures used to achieve this and their effectiveness will be reviewed on the basis of the groundwork provided by Regine Röthlisberger.

Regine Röthlisberger also has guidelines for the greenhouse gas inventory. They concern the data that are collected and how they should be prepared, interpreted and calibrated. This is precisely what she has in the 7 folders mentioned earlier. To describe the greenhouse gas emissions from fossil fuels, Regine Röthlisberger and her colleagues compiled data from the areas of households, services and commerce, industry and transport. The energy statistics of the Swiss Federal Office of Energy serve as the basis for this work. In addition, they use figures to show the quantities of greenhouse gases that are generated by the use of substitute materials for chlorofluorocarbons (CFCs) or by agriculture. In the latter case, this involves data on the number of livestock animals and their specific feed.

When asked how many data sets are included in the greenhouse gas inventory, Regine Röthlisberger stretches her hands far apart and estimates about 1,000, and growing: “Knowledge and experience with methods of estimating greenhouse gas emissions are constantly growing”, says the expert.

Solid groundwork for political decisions

Science and administration both want precise data on climate and its development. But how well do they work together? Regine Röthlisberger says: “When we set long-term goals as an administrative body or initiate climate change adaptation measures, we are guided by scientific principles.” In her daily work, however, she only occasionally works with scientists. Likewise, Stefan Brönnimann of the University of Bern acknowledges that there are only a few points of contact. Nevertheless, both parties are working independently toward the same goal and support each other in this effort with precise data from thousands of different sources. They do so to guide policy-making and provide support.

Further information

Last modification 11.02.2015

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