by Gracie Williams
On Tuesday, The University of Georgia Skidaway Institute of Oceanography hosted a talk as part of their 2019 speaker series. Dr. Daniel Ohnemus discussed climate modeling in his lecture titled “Understanding Climate Models – History, Forcings and the Future.”
Ohnemus is a Cape Cod native, and performed his undergraduate work at William’s College in Williamstown, Massachusetts. Then he returned home to receive his PHD from the MIT Woods Hole Joint Program. Ohnemus is a Biogeochemist with a focus on trace elements in the ocean.
This is the first time he’s given a public lecture on climate models, although it has been a hobby of his for a while. “These models are an important aspect that oceanographers, and even many environmental scientists, have to deal with. They operate at such a high level of our understanding and combine a lot of different aspects of oceanography, earth science, mathematics and physics,” Ohnemus said.
Models are computer simulations of the real world, but they don’t capture an immense amount of details. They are inherently simplifications of grander processes. These models are complex and expensive to run, so getting them up and going is often a deliberate effort. Their purpose is to answer a specific question about a sensitivity or certain aspect.
Ohnemus explained that in global climate modeling, there are a lot of things to consider. Topics such as global warming and climate change tend to arouse human interest. There is a lot of passion in these subjects, but climate models consider the natural earth systems aspect of the process. Essentially, they stick to the basics of the planet. What they don’t consider is the economy, the health impacts of different changes in global climate or different pathways of human energies. The climate will naturally respond to these factors but won’t directly involve human impact. Climate models aren’t designed to understand the impacts they might have on human populations especially the effects rising sea levels may have on the placement of future settlements.
Why are we thinking about these things? Why do they matter? The intergovernmental panel on climate change has five major metrics for what climate impacts, and they determine what we should care about.
The first one is the gross global temperature of the planet. From year to year there is a large range in temperature, mostly due to El Niño and changes in ocean circulation, and this is normal. But it is not until you look at the larger data set that you see big changes— only then it is clear that the temperatures are drastically rising.
The second is the loss of Arctic sea ice. Due to a rise in temperatures, ice is melting and thinning. On average in the last 25 years, sea ice is about 40-50% thinner, and those numbers are concerning.
The third is what changes and averages do to extreme weather. In current time, not only is the planet hotter, but the extreme weather is as well. These events can be dangerous, and continue to be a major concern to governments worldwide.
The fourth is the fact that sea levels are rising about three and a half millimeters per year. This is driven by land and sea ice cover, and the warming of the oceans. The heat that the oceans absorb makes them expand, and therefore they rise.
The fifth is the composition of the atmosphere. One model has been reporting the concentration of carbon dioxide in the atmosphere, and the larger trend of the curve over time is largely due to human emissions.
Today, there is currently debate about specific units such as the ocean, and what the most unbiased way of training them is. With any of those things, it comes down to how you want to validate it. “Any model is only as useful as the questions you want to answer with it,” Ohnemus said.
To learn more about upcoming events hosted by the institute, you can visit their website.
