Moritz Günther

Department Climate Physics IMPRS
Group Global Circulation and Climate
Position Phd Candidate
phone +49 40 41173-106
Email moritz.guenther@mpimet.mpg.de
Room B 307

Research

Large volcanic eruptions can enhance the stratospheric aerosol layer, which has a net cooling effect on the Earth, mainly through reflection of sunlight. My research is motivated by the surprising finding from many model studies that volcanic aerosol forcing seems to lead to more stabilizing feedback than radiative forcing from CO2. In other words: A certain radiative perturbation (in W/m2) from aerosols leads to a smaller global mean temperature change than a radiative perturbation of the same magnitude from CO2.

This phenomenon is linked to the pattern effect: Not all places on Earth warm or cool equally fast, and the pattern of these temperature changes sets the feedback strength. Together with my supervisors Hauke Schmidt, Claudia Timmreck, and Matthew Toohey, I explore the relationship between radiative forcing, temperature pattern, and feedback. How do different temperature patterns come about? How sensitive are they to different forcing patterns, forcing agents (i.e. stratospheric aerosol, CO2), and background states? How do these temperature patterns affect the general circulation and feedbacks? Which regions are most important in setting the response? What are the implications for the pattern effects of CO2 and volcanic aerosol forcing?

 

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

 

 

Further information

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.

 

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