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Climate change

1.5 degree could already be exceeded in the next few years

A stream full of meltwater makes its way across the Greenland Ice Sheet. Bild: Ian Joughin/imaggeo.egu.eu

In the Paris Climate Agreement, the global community agreed to limit global warming to a maximum of 1.5 degrees. A new report by the World Meteorological Organization (WMO) predicts that this value could be exceeded as early as 2026.

The World Meteorological Organization (WMO) has published a new climate report and again warns that the 1.5 °C threshold may be exceeded. According to the report, average temperatures could exceed 1.5 degrees at times in the next five years. The probability that this will happen at least once in the next five years is 50%. The 1.5°C value is an indicator of the point at which climate impacts become increasingly harmful to humans and the planet as a whole. The WMO supports these findings with updated numerical values. What does the report mean and how does it complement those of the Intergovernmental Panel on Climate Change (IPCC)? We spoke with Hans-Otto Pörtner of the Alfred Wegener Institute for Polar and Marine Research in the Helmholtz Association. Pörtner has been a lead author on the IPCC reports for years.

Prof. Pörtner, what distinguishes the current WMO report from the just released IPCC study ?

The WMO has an international working group of eleven climate research working groups that issues an annual update, over and above the IPCC reports, on the extent to which the IPCC's projections are accurate and how the near future will develop. It is an annual update, complementary to the IPCC studies.

The WMO gives a 93 percent probability that one of the years between 2022 and 2026 will be the warmest year since modern weather records began. Also with a 93 percent probability, the five-year average for 2022 to 2026 will exceed that of the last five years from 2017 to 2021. How do percentages like that come about?

The current projection that we will see a year that averages 1.5 degrees of global warming or more over the next five years is ultimately a statement that comes from climate models that can calculate such probabilities with sufficient accuracy, taking into account existing climate variability. And that probability is 50%. What that statement means is that we are approaching that threshold of 1.5 degrees with global warming. It also means that as we move closer and closer to that threshold, we will then exceed it at points with higher and higher probability, on a global average.

You coordinated the IPCC special report on 1.5 °C. How did this special report come about?

At the time, the report arose from an invitation from the UNFCCC Framework Convention on Climate Change because there was not enough knowledge available for scenarios below 2 °C warming. This gap was to be filled. The invitation was made at the 2015 Paris Conference and the IPCC accepted it for the 6th reporting cycle. It was a successful effort in that it was the first time that 1.5 °C was attempted to be calculated and evaluated. We did a comparison of the scenarios for 1.5 and 2 °C global warming and were ourselves very surprised at how big the differences are between these scenarios and how much the numerically seemingly small difference has an impact.

The number around which everything revolves: 1.5 °C. WMO Secretary-General Petteri Taalas says, "The 1.5 °C figure is not a random statistical value. " What does that mean?

Hans-Otto Pörtner is head of the Department of Integrative Ecophysiology at the Alfred Wegener Institute for Polar and Marine Research. He has collaborated on various IPCC reports. He was lead author and coordinating lead author on the IPCC Fourth and Fifth Assessment Reports. Picture AWI

The goal of limiting global warming to a maximum of 1.5 degrees is derived from a comprehensive look at the effects of climate change. A coalition of the willing, led by the small island states, had introduced the tightening of the climate target in Paris: not simply 2 °C, but staying well below that with the goal of not exceeding 1.5 °C warming. In the special report on 1.5 °C, we brought together findings with the other IPCC working groups, from global warming and its impacts to ways to limit climate change under the overarching.

What scenarios are needed to hold to 1.5°C?

Our report and also the WMO update show: we are on the brink. We see that political and societal decision-making processes are very sluggish. It worries us that these numerical climate targets are not taken seriously enough by politicians. From the risk assessment that we adopted in the IPCC Working Group II Assessment Report at the end of February/beginning of March this year, we can see very clearly that we are exceeding the upper limit of our "normal range" by exceeding 1.5 degrees.

The AWI has brought back disturbing information from the Arctic with the MOSAiC expedition. In its report, the WMO also sees dramatic developments north of the Arctic Circle. "What happens in the Arctic doesn't stay in the Arctic" is a common saying from the AWI. What is happening in the far north, and how does it affect us in Europe?

We see an increasing destabilization of sea ice cover and a decrease in area. We see a change in ecosystems, in plankton activity, in wildlife. The trend of decreasing sea ice cover will lead to a decrease in the re-radiation of heat from the white surface, causing this ocean area to warm more. Ultimately, this will also have climatic effects. Known to be altered by climate change is the circulation in the high atmosphere, the jet stream, which controls the position and rate of displacement of weather systems. In the northern hemisphere, areas of high or low pressure often become trapped and do not move forward. This results in heat waves worldwide with thousands of deaths, warm Arctic winters and cold waves in North America, as well as droughts and flash floods in our region. This shows us that a global change in the earth's climate has long since been set in motion.

For the year 2022, the periodically occurring climate phenomenon La Niña is expected to slightly lower the global mean temperature. La Niña is usually associated with increased drought in southwestern Europe and southwestern North America, where drought is already prevalent. In northern Europe and Australia, however, WMO experts foresee wetter conditions than the long-term average. Will we have to get used to burning forests in Spain and California and flooding in Australia?

We do indeed have increasing fire risks. Forest fires are natural events to begin with, but the intensity and area affected is increasing. In Australia, we've seen tremendous area destruction by fire, with corresponding impacts on the natural environment and deaths of millions, billions of animals. These are proportions that we would not have had without climate change. That's true in other regions as well. Increasing drought, the uneven distribution of precipitation is also being felt, sometimes seasonally intensified.

When we talk about climate, we talk about meteorological averages. The WMO has set an averaging period of 30 years for this purpose. For the past two years, the period 1991 - 2020 has been considered the reference period. Is that a suitable measure?

We have a reference period in the IPCC that we call pre-industrial, where we refer to 1850 - 1900 when we talk about the extent of global warming. We keep that reference period. But as a biologist, I also look at the much larger time scale of evolution. What is life on Earth adapted to, and what variability has life had in, say, the last 800,000 years, where we've had a regular alternation between ice ages and warm ages? What is important here is the Holocene period, the last 11,000 to 12,000 years, when human civilization developed and our species spread across the globe. We are now seeing, as effects of the climate change we are creating, that we are leaving the Holocene. As a result, we are losing habitat for nature, and therefore for humans.

You have worked in a leading role on various reports of the Intergovernmental Panel on Climate Change (IPCC). The current WMO report describes climate mainly as an atmospheric issue. At AWI, you head the Department of Integrative Ecophysiology. Your work makes it clear that the climate crisis is not just about atmospheric science. Wouldn't sustainability crisis be a better term to describe a broad threat we face?

We need to think of ourselves as part of the Earth system. Climate is not just atmosphere, water and ice, but also biosphere and soils. All of these subsystems are tipping out of balance right now. What worries me most as a physiologist is the hopeless exposure to extreme temperatures that can ultimately, even if it is temporary, make a habitat uninhabitable for animals, plants and humans. This planet is characterized by a conducive climate for living nature, otherwise life would not have evolved here and it would look like Mars. It is up to us to shape our natural environment in such a way that our livelihoods are preserved.

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