The team analysed the outcomes of 40 different climate models, which will also be used in the upcoming sixth Assessment Report from the IPCC . The simulations are based on the implementation of various climate protection measures by 2100. In this regard, more intensive climate protection paths with lower emissions correspond to scenarios in which the 1.5°C or the 2° C goal can be reached; weaker climate protection paths correspond to a business-as-usual scenario, which means a global warming of 3-5° C by the end of the century. One surprising finding presented in the study: even with ambitious climate protection measures, before 2050 the Arctic sea ice could largely melt in some summers, to the extent that the Arctic could be considered ice-free (less than one million km² of sea ice in September). Some model runs even indicate an ice-free Arctic before 2030. This would be a change with far-reaching ramifications for the Arctic, but also for the global climate. The Arctic is considered to be the ‘early-warning system’ for global climate change and, because of radiative feedbacks in the sea ice, a critical determinant for the speed of climate warming. Due to feedbacks in the climate system, these changes would also have major effects on the climate of the Northern Hemisphere, particularly for Germany and the rest of Europe.
meereisportal.de talked with Dirk Notz about the outcomes of the study and asked for his opinion on future developments:
Mr Notz, how did the study come about, and what was its main goal?
Dirk Notz: A few years back, we met with other sea-ice modellers and discussed how we could use our climate models to learn more about sea ice. There was a strong consensus that coordinated simulations, which included as much detailed information on sea ice as possible, could be extremely helpful. This led to the Sea-Ice Model Intercomparison Project (SIMIP), which is now being carried out in the framework of the latest model comparison, CMIP6. Our study has yielded the first results of the project.
What’s new about your study in comparison to the outcomes of the model comparison project (CMIP5) for the IPCC Assessment Report from 2013?
Dirk Notz: When it came to analysing the outcomes, the joint approach allowed us to cover an extremely broad spectrum of expertise and field experience. This resulted in what I personally consider to be a very balanced analysis, one that indicates that, at least for individual years, the complete loss of Arctic sea ice in the summer can no longer be avoided. We’d never before been able to show this aspect so clearly.
In the analysis of your study, a linear correlation between changes in cumulative CO2 emissions and sea-ice retreat during the timeframe 1979 to 2015 is assumed. How is this relation to be understood? Isn’t sea-ice development also directly related to the global warming produced by rising CO2 emissions?
Dirk Notz: The development of Arctic sea ice is above all directly dependent on the status of the climate system. When it gets warmer, the ice melts – and there is in fact a linear correlation between the sea-ice extent in the Arctic and mean global temperature. Over the past 40 years, every degree Celsius of global warming has caused the summertime sea-ice extent to shrink by ca. 4 million km2. On the other hand, the correlation between global warming and CO2 emissions is now nearly linear, which means the sea-ice extent is also linearly dependent on emissions levels. In this regard, observations indicate a loss of roughly 3 m2 of sea ice for every metric ton of CO2 released. In reality, of course, a corresponding volume of ice is melted, but we don’t yet have sufficiently long time series to reliably quantify the relation.
In your opinion, what will the consequences of sporadic ice-free summers in the Arctic before 2030 be?
Dirk Notz: We can’t say exactly when the Arctic will have its first ice-free summer, because natural variations from one year to the next overlap with the wide-scale climate change. However, the most probable timeframe is somewhere between 2030 and 2050. That being said, the exact year in which it happens isn’t particularly important. What’s certain is that, once the summer ice is lost, the landscape form “permanent ice pack cover” will no longer exist, and will be replaced by “seasonal ice pack cover”. Every element of the Arctic ecosystem that requires permanent ice cover will then have to adapt or disappear – the ecosystem as we now know it will be lost.
In addition to the potential ecological consequences, I also see significant cultural impacts: we all think of the Arctic as an ice-covered frontier that exerts an almost irresistible fascination. It’s no coincidence that children (and not just children!) are so spellbound by reports on the Arctic and the research we do there. In the future, the frontier as we know it will no longer be there. In the summer, the majority of the Arctic will be simply be ocean, and we’ll be able to take ships to the North Pole and look at the water there. At least in summer, the beauty and fascination of the Arctic will be lost.
Can the projected, drastic loss of sea ice in the Arctic still be prevented by climate protection measures, or have we already passed this tipping point in the climate system?
Dirk Notz: For us researchers, the loss of sea-ice isn’t actually a tipping point, because it directly and linearly depends on the development of warming and CO2 emissions – until there’s no ice left. We can only stop the loss of ice by stopping the warming, and from a physics perspective, we can only do so by reducing our net CO2 emissions to zero. Until that happens, the ice loss will continue. Our study shows that, from a scientific standpoint, it’s now highly unlikely that we’ll make the necessary reductions in time to prevent an ice-free Arctic in the summer. However, what we can still do is prevent it from becoming the norm. If we can manage that, we can preserve at least part of the Arctic’s stunning beauty and fascination for future generations…
Thanks so much for the interview!
Prof. Dr. Dirk Notz (Universität Hamburg)