What happens when the temperature of the ocean rises by half a degree?

Peter Pfleiderer, Photo: Falk Weiß

Peter Pfleiderer

In 2017, the hurricane season saw an especially large number of storms, which appeared in close succession, several of which were extremely intense. Six of these were major hurricanes in categories three to five, and on the 8th of September three hurricanes, Katia, Irma and Hose, rampaged at the same time over the Atlantic. In total, more than 3,000 people died during that storm season and the economic damages amounted to more than $200 billion US dollars. I am interested in the question of whether a storm season like the one in 2017 will become more common in the future as a result of climate change.

To investigate this, one must first understand how hurricanes originate and how they develop. We do know, for instance, that the surface temperature of the ocean influences the wind speed and thus the destructive force of these storms. Category five hurricanes can have wind speeds reaching over 300 kilometres an hour. Climate change affects weather conditions, which can lead to higher ocean temperatures and more water vapour in the atmosphere, which in turn can lead to violent hurricanes.

Using climate models, we can calculate how high the probability of such extreme weather events is in certain climate scenarios. By simulating current climate conditions over 10,000 years, we can calculate, for example, how often heatwaves can be expected and how intense they will be. We then compare these results with simulations of anticipated future climate conditions, or the conditions of a climate where there is no human influence. Based on these differences we can make predictions about whether extreme conditions will become more common in the future.
For tropical storms, too, equivalent simulations using climate models would be possible. To date, however, there are seldom climate models that adequately show such results. Even within only a small section, a hurricane has very different wind speeds, and the intensity of rain also varies significantly within the storm area. As such, it is incredibly complex to correctly represent such phenomena in a model. This is why I have created my own model that takes data like weather, ocean temperatures, and atmospheric conditions, and uses it to approximate storms. I can use this model as an extension of the larger climate models to simulate the development of hurricanes under specific weather conditions.

These simulations mean a lot of working on the computer. Every character and every line of the code I write must be flawless in order for the model to make storm projections as accurately as possible. Of course, there is always something that can be improved. Afterwards, I compare my model with past weather and satellite data and by so doing, I can verify if it accurately depicts reality. For a single modelling program, the work cycle of programming, simulating and comparing can take several weeks.

Only when the model is operating appropriately can you apply yourself to the really exciting questions. What happens when the surface temperature of the ocean rises by half a degree? Or if it sinks? Will climate change cause more frequent hurricanes and will they get stronger overall?
So far, many indicators have shown that the storms over the Atlantic will get stronger. In the coming decades, the surface temperature of the oceans will rise, and this is what gives the storms their strength. Warmer air transports more water, so the amount of rain and floods will increase. Combined with rising sea levels, this is not a great outlook, particularly for the island states of the Caribbean. Another question, though, is whether the storms will become more frequent. Climate researchers are not in unanimous agreement. We need more and better data in order to make more accurate predictions.


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