Moritz Günther
| Department | Climate Dynamics |
| Group | Director's Research Group (CDY) |
| Position | Postdoc |
| phone | +49 40 41173-313 |
| moritz.guenther@mpimet.mpg.de | |
| Room | B 307 |
Research
Under climate forcing, not all places on Earth warm or cool equally fast, and the pattern of these surface temperature changes controls important aspects of atmospheric circulation and cloudiness ("pattern effect"). Most importantly, the temperature pattern influences the climate feedback parameter and therefore climate sensitivity, i.e., how much Earth changes its temperature in response to radiative perturbations. In my research I explore the formation of patterns of sea surface temperatures, as well as their consequences for feedbacks and climate sensitivity.
My current research is aimed at understanding the evolution of the pattern of surface temperatures in the future, because it critically influences how much the Earth will warm in response to greenhouse gases. Will the currently observed pattern of strong Western Pacific warming continue, or will it, as suggested by an extensive body of literature, switch to Eastern Pacific warming? If there is a transition, when will it happen, and which processes determine its time scale? Specifically, how do energy flux differences over land and ocean affect the general circulation, and how do these circulations impact the temperature pattern?
In my PhD thesis, I explored the pattern effect in the aftermath of volcanic eruptions. Large volcanic eruptions can add reflective aerosol to the stratosphere, which cools the Earth for a short time (~years). I showed that different patterns of surface temperatures arise in response to forcing from stratospheric aerosol than in response to CO2 forcing. I explained the origins of these differences, which involve the stratospheric overturning circulation (Brewer-Dobson circulation) and its effects on the troposphere. Furthermore, I showed how the pattern differences explain why a certain radiative perturbation (in W/m2) from stratospheric aerosol leads to a smaller global mean temperature change than a radiative perturbation of the same magnitude from CO2.
Inspired by the xkcd comic using only the 1000 most common English words to explain the Saturn 5 rocket.
Some large rocks can burst out and put fire and smoke into the air, and I will call them fire rocks. Sometimes, the fire rocks also give off little drops in the higher part of the air, which stay there for a few years. Sun light has a hard time passing through these drops, and this makes the world a bit darker. When the fire rocks give off sun blocking drops, we would expect the world to get quite a lot colder, because the world now gets a lot less power from the sun. However, it actually gets only a bit colder: the change is less than we would expect. In order to find out why, I use a computer to study how the world would respond to the sun-blocking drops.
The small cooling can be explained by the fact that some places of the world cool faster than others. One key place is that part of the world where the water is the warmest. On a paper that shows all the world's land and water, this place is in the left part of the largest water body. I will call it the warm water place. The drops that come from the fire rocks cool down the warm water place very much. When the warm water place cools down a lot, the rest of the world can remain more or less how it was before, because the warm water place has a strong control over the rest of the world. Over the warm water place there is a lot of up-going air, which means that it is well tied to the air that is closer to space. For this reason, the warm water place can even out the cooling very well, much better than any other place in the world.
Making the world darker with these drops is a way to make the world colder, but we are most used to the case where the world gets warmer because humans put warming smoke into the air. We can put a number on the forces that are caused by the warming smoke and the cooling drops. In the end, warming and cooling are the same thing, just with a different sign, so we can look at them side by side. The forcing that comes from the warming smoke does not leave such a strong mark on the warm water place, and for this reason it is very good at making the world hotter. On the other hand, the warm water place responds in a strong way to the cooling drops that block the sun light, and this makes the cooling drops very bad at cooling the world.
Links
- Google Scholar
- CV (last updated on 23 October 2024)
- Twitter (@MoritzGnther7)
- Mastodon (@moritzguenther@mastodon.world)
- Github (moritz-g): Parts of my code are on github. All my first-authored publications contain links to the complete code that was used to produce all results and, if I own the rights, to the underlying data / model output.
Climate feedback to stratospheric aerosol forcing: the key role of the pattern effect
In a recent study Moritz Günther, Hauke Schmidt, Claudia Timmreck (all MPI-M), and Matthew Toohey (University of Saskatchewan) argue why the cooling following large volcanic eruptions is smaller than what one might expect from simple energy balance arguments.
