"Humanity has to abandon all its stalling tactics."

Mr Pörtner, you’ve read the new report from your colleagues from Working Group I from two perspectives: as a marine biologist, and as Co-Chair of IPCC Working Group II. In your opinion, what are the most important new findings on the physics of climate?

Hans-Otto Pörtner: In my eyes, the report makes three essential contributions. Firstly, Working Group I has succeeded in zeroing in on climate sensitivity. That means we can now say with more certainty to what extent a given rise in carbon dioxide concentration will warm the atmosphere. A second central aspect: the scientific community can now say how likely it is that individual events like the major fires in Australia or the heat wave in western North America are the result of climate change. The climate debate no longer focuses solely on the rise in the global mean temperature, but also and especially on extreme events and how they’re changing in comparison to the past. A third essential piece of information lies in the recognition that some of these events are more dangerous than previously assumed. Hopefully this last finding will help many people to grasp that climate change is here, that it can already produce extremes, and that it will ultimately do tremendous damage and cost human lives. Speaking on behalf of Working Group II, I feel that one of the new report’s strengths is the fact that Working Group I especially focused on those climate variables that could potentially impact ecosystems and human beings, and systematically prepared information on those variables. By doing so, it created an important link to the report from Working Group II, which will be published in February of next year.

One aspect that has caused quite a stir and considerable confusion is that, in response to new findings on Earth’s climate history, Working Group I has now adjusted the temperature value for the preindustrial era – that is, the value that all current measurements are compared with. This step, together with the rapid warming over the past two decades, has now led to the claim that the 1.5-degree mark will likely be reached ten years earlier than previously projected. How do you assess this methodological change and its potential consequences?  

First of all, it’s both sensible and perfectly understandable for Working Group I to do everything it can to make numerical statements on the temperature and other climate variables more precise; they are, after all, part of climate physics. Nevertheless, the decision to slightly adjust the basis of the temperature scale definitely gives me headaches, especially when we’re talking about those temperature values that are discussed in connection with the Paris Agreement. Adjusting the scale by 0.08 degrees Celsius required intensive discussions across all three IPCC Working Groups, because it naturally also raised the question for us of whether the Paris climate target was still 1.5 degrees Celsius, or whether we were now talking about 1.58 degrees Celsius, and what consequences taking this step would have for all statements made on the basis of the old 1.5-degree mark.

And what did you conclude?

All of the target values in the Paris Agreement were set with a view to the climate impacts. In other words, the primary question was which risks and impacts could be mitigated if the world limited global warming, ideally to 1.5 degrees Celsius. When the initial basis is adjusted by 0.08 degrees Celsius, the temperature level for all corresponding effects also shifts slightly. That means: now, when Working Group I says that a warming of 1.5 degrees Celsius may come ten years earlier than previously assumed, it doesn’t mean that the projected effects of a 1.5-degree temperature rise will also be felt ten years earlier. On our impacts scale, the new figure is also connected to the effects of a 1.42-degree increase, since both the numerical value and the temperature scale have changed slightly. Conversely, in the 1.5-degree report we said that the timeframe in which the 1.5-degree mark would be reached was between 2030 and 2052. Viewed in this light, the demonstrable acceleration of global warming should motivate us to abandon all our stalling tactics when it comes to climate protection.

Does that mean that, in your eyes, the climate target set in Paris remains the benchmark for all potential climate protection measures?

There’s simply no alternative to the climate target set in Paris, as the current extreme weather events underscore day after day. In my opinion, anyone who still feels climate change isn’t their problem is guilty of criminal negligence. We have to pursue climate protection on every possible front and tap every available option. This includes using all available technologies, as well as changing our eating habits. It also means maximising our adaptation measures. Just how urgently this is needed can also be seen in the latest heat wave: all of the recent heat-related fatalities in North America could have been avoided with suitable adaptation measures. In its 5^th Assessment Report, released back in 2013/2014, the IPCC stated that humanity had the necessary funds and technical means, even if in many cases the technologies hadn’t yet been deployed at the required scale.

Nevertheless, the number of measures that have actually been implemented is still lagging far behind the promises made.

The real problem with human beings is that, when in doubt, we still believe we can keep doing things just like we always have. Personally, I question that attitude. Let’s consider the climate crisis in terms of the coronavirus pandemic, where, as we all know, we go into lockdown when the infection rates get out of hand. Who’s to say that, if we can’t manage a climate transformation in time, there won’t have to be a climate lockdown in order to avoid a more drastic climate change and its effects? This type of lockdown would mean having to suspend all activities that produce substantial emissions in order to achieve dramatic emissions reductions and stay on the 1.5-degree path. And just consider the time scale that would be required – it would be much longer than for COVID. Let me say it again, in no uncertain terms: you can’t negotiate with climate physics, or with the biology of human beings and other life forms. If we don’t accept that fact and act accordingly, we’re going to very quickly find ourselves in a situation where our back is to the wall.