Is there a specific reason why this report is being published right now?
Representatives of the governments that make up the IPCC decided in 2016 that the IPCC should draw up three special reports in addition to the progress reports. One of them deals with the ocean and the cryosphere, both key elements in the Earth system. They are not only important for the climate, but also for the preservation of life on earth. Oceans cover more than 70 percent of the Earth’s surface. And there would be no higher life without the ocean. Marine phytoplankton is also responsible for about 50 percent of the global primary production of biomass and therefore for half of the global oxygen production on Earth. In turn, the cryosphere stores large quantities of fresh water and is indispensable for life on land.

You are Swiss, have studied in Zurich and received your doctorate in Bern. How is it that you have specialized in oceans as an inland inhabitant?
For many people in Switzerland, the ocean seems to be far away. But we are also dependent on the function it fulfils in the Earth system. Tens of millions of people worldwide depend directly on the state of the ocean. Among other things, it is responsible for the weather and climate, and it is an important resource for food and water. However, it also plays an important part in sectors such as energy, trade, transport, leisure and tourism. And its state affects the health and well-being of countless people. But in contrast to the land or the atmosphere we still know very little about the ocean. In particular, how climate change affects the biogeochemical conditions of the ocean and its ecosystems. It is precisely these unanswered questions, the unknown, that fascinate me.

Without wishing to pre-empt the report: What consequences does climate change have on fish stocks and therefore on an important livelihood for a large part of the world's population?
We know that the oceans have become much warmer and that this warming will continue to increase in the future. As a result, some fish have to find a new habitat. They migrate towards the poles and into deeper waters. This development has already been demonstrated in various marine areas.

How do you actually become the lead author of an IPCC report?
Experts from all over the world can respond to a public tender. The leadership of the IPCC Working Group II, which explores the socio-economic and natural system’s vulnerability to climate change, selects a handful of experts from this pool. The assembled team jointly identifies and writes the special report’s various chapters.

What exactly was your job as lead author?
Together with other experts, I was able to write the chapter on "Extremes, abrupt changes and managing risks". In doing so, we relied on existing knowledge and made use of studies published in scientifically peer-reviewed journals, as far as possible. As a chapter team, we then had to agree on the presentation of the compiled state of affairs and its scientific evaluation. This is an intensive process in which sometimes different views clash. However, contrary opinions, gaps in knowledge and uncertainties are clearly presented in the report. It is also checked several times using a multi-stage review procedure. The first review is carried out by external scientific experts, while the second also involves government experts. A summary is produced for policy makers in the final step with the preparation of the report. This text is finally adopted sentence by sentence by the governments in a General Assembly. This General Assembly, which I also attended, was held in Monaco last week. It was chaired by the scientists.

How were the authors of this special report selected, can all specialists participate? As a lead author one can call in "contributing authors", who support us scientifically with a certain fact. For example, we brought a coral expert on board for the subject of marine heat waves to help us summarize our knowledge of the effects of marine heat waves on warm water corals. All researchers, including those who did not work directly on the report, were then able to comment on the text during the review procedure.