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An Interview with Palaeoclimate Modeler, Hu Yang

Here, we chat with Dr. Hu Yang about his recent publication in PLOS ONE and his predictions of the future of the Greenland Ice Sheet – the second largest body of ice on Earth, which has the potential to dramatically raise global sea level.

Dr Hu Yang is a research scientist in the Paleoclimate Dynamics group at the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research. His research interests include climate dynamics, sea-level change and paleoclimate change. To gather his results, he is particularly focused on combining observations with numerical model simulations. Dr Yang’s studies, including the discovery of a poleward shift in major ocean currents, the interpretation of tropical expansion and reconstruction of the Greenland ice sheet evolution have gained widespread attention and recognition.

Your recent paper published in PLOS ONE focuses on the Greenland Ice Sheet (GrIS) – can you tell us a bit about the ice sheet, how it is changing and what this means for global climate change? 

HY: The GrIS holds a huge amount of ice which has the potential to raise sea level by 7.3 m if it completely melts away. Understanding the GrIS’s response to climate change, therefore, is critically important for us to understand how future sea level will rise. In our study, we revisited the past evolution of the GrIS using numerical model simulations and compared it with geological reconstruction. The results show that the ice volume response of the GrIS (the amplitude of the melting and sea level rise) strongly delayed climate change, which is on the order of thousands of years. That means if we warm our planet within 100 years, the sea level rise within our generation will be minor. However, the rising sea level can last for quite a long period of time, with a much larger amplitude.

Could you explain, how does the response of the Greenland ice volume delay climate change?

HY: The Greenland ice sheet has been standing there for at least 3 million years. The mass balance of the ice sheet is determined by the surface mass gain (snowfall) and mass loss (melting and ice discharge) at its margin. Ice melt usually only takes place at the margins of the ice sheet during a few months in summer. The inner portion or the summit of the ice sheet almost never melts, because of high elevation and cold temperature. When climate warms, it removes the ice from the margin, then more ice will flow down to the margin and begin to melt. This process takes time – not a few decades, but hundreds or even thousands of years. According to the latest IPCC report, in the worst warming scenario, sea level rise within this century will be around 1-2 meters. But geological evidence suggests that the Greenland and Antarctic Ice Sheets will both be melted away if that kind of worst warming stabilized. So, there is a delay for the melt of the ice sheet and sea level rise.

How does an understanding of past climates help us to better understand future changes to the Earth’s environment? 

HY: As a human-being, most of us believe what we see within our lifetime, which is usually less than 100 years. But, 100 years relative to Earth’s history is only equivalent to a minute of time in a person’s life. If we only check one minute’s behavior of a person, we will not be able to get a comprehensive understanding of his personality. For the same reason, an understanding of past climates informs us about the current status, and how it could evolve under the forcing of rapidly rising greenhouse gases.

In the case of the Greenland ice sheet, the past ice evolution tells us that the GrIS is currently at its biggest size within at least the past 7000 years. It will shrink in response to the committed warming. And this shrinking could continue for a long period of time, even if the warming stabilized at the current level.

We have recently seen examples where the unprecedented rate of change to a number of environments has in turn made it more difficult to study those environments – for example, ice breaking off of the Thwaites glacier in the Antarctic is preventing research ships from accessing it. Do you foresee similar challenges in studying the GrIS, as it continues to melt? 

HY: The Antarctic ice sheet is different from the GrIS. The Antarctic ice mostly terminates into the ocean, but most of the margins of the GrIS stop on land. So, I don’t see similar challenges. But unlike the Antarctic ice sheet, which has almost no surface melt, the surface melt of the Greenland ice sheet may produce large river discharge, which may cause problems, perhaps.

Your study utilized openly available models and data to simulate changes to the ice sheet – do you think that Open Data and code/model sharing is important for our improved understanding of global environmental change? 

HY: Definitely, open sharing of data, models and research outputs, accelerate the advance of science.  I can hardly imagine how scientists did research one century ago. I hope in the future, all the journals could make their publications open access, like PLOS ONE, to promote the transformation of knowledge.

Dr Yang holds ocean sediment, from which researchers can extract information about past climates.

Given new and unpredicted changes that have arisen on the GrIS – for example, last year, rain fell on the ice sheet for the first time that we know of – how will existing models account for this? Or do we need ever-changing models? 

HY: There is no best model, but always a better model. Model developing takes decades. Development of climate models started more than half a century ago, and are still developing with higher resolution and new physical parameterizations. Ice sheet modelling is relatively new compared to climate modelling. A lot of processes have not been taken into account, such as rain and the meltwater pool. However, the current ice sheet model can already simulate the general geometry and ice velocity resembling observations. And with more and more processes included in the system, we could expect to have more and more accurate results.  

Have you had an opportunity to do fieldwork on the Ice Sheet yourself? 

HY: Unfortunately, not yet. This seems odd for a scientist doing ice sheet research without ever doing fieldwork on it. But today, scientific research is so specialized. For example, in our team, we have colleagues who have a background in geology. We also have experts on climate dynamics and ice sheet dynamics and computer science. Cooperation between multidisciplinary fields will fill the knowledge gaps and make research easier.

What do you find to be the most challenging aspect of being an Early Career Researcher? 

HY: Currently, I find the most challenging aspect is to find a good balance between funding and doing research. The best science is not planned, it needs time not only for developing the idea, but also for publishing. The newest idea usually takes more time to get published. But, a common working contract for an Early Career Researcher usually lasts for only 2-3 years. When I got my Greenland paper published, the project that supported this study had already been expired for two years already.

Reference: Yang H, Krebs-Kanzow U, Kleiner T, Sidorenko D, Rodehacke CB, Shi X, et al. (2022) Impact of paleoclimate on present and future evolution of the Greenland Ice Sheet. PLoS ONE 17(1): e0259816.

Disclaimer: Views expressed by contributors are solely those of individual contributors, and not necessarily those of PLOS.

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