Greening of the Desert: Open Climate Models (1)

Greening of the Desert: Open Climate Models (1)

A couple of years ago a student of mine brought me the following problem. He described a project where desalinization plants would be built off of the West Coast of Africa. The water would be used to irrigate the Western Sahara for agriculture. The project proposer realized this would change, in a fundamental way, the surface of the Earth. Presumably it would change from white reflective sand to green absorbing leaves. And there would be huge changes in the water.

The person proposing the project knew that there was a relation between the Sahara and hurricanes in the North Atlantic. The question posed was whether or not there might be a weakening of the hurricanes, and perhaps, the project might engender support because of this. Of course there would also be the possibility of increased risk, and opposition to project.


Figure 1. Schematic of African Easterly Waves that I use in dynamics class, but I forget where I got it originally.


In a general sense, this is not a crazy question. The Sahara is an important ingredient of regional climate. There is enough heating in the Sahara that the normal condition of temperature decreasing as you move away from the equator is reversed during the summer, leading to the conditions that cause African easterly waves, which do influence the generation of hurricanes. But there are other influences of the Sahara that are more direct. Even the Romans talked about dust from the Sahara influencing Europe. Therefore, a large regional agricultural or energy project that altered the surface of the Sahara is likely to have regional, perhaps even global, climate effects. There might be benefit, or damage, or risk, or liability.

If we are to imagine alternative energy sources like wind and solar being built to large enough scales to displace fossil fuels, then that will require huge alterations to the surface of the Earth. In 2005 David Keith investigated changes that would occur if wind farms were placed near population centers in the Northern Hemisphere; these covered 10% of the land surface. Nathan Lewis on his web site talks about the scale of the projects needed for alternative energy projects.

The Keith et al. paper referenced above is the type of simulation that is needed when preparing for climate change, new energy systems, and providing energy and food for increasing population. That is, we have to alter the surface of the Earth in some significant way, and then compare, for example, the costs and risks of wind energy, to using other types of energy, including continued emissions of carbon dioxide from burning fossil fuels. Regional climate impacts also need to be investigated fully.

If you compare this sort of simulation to weather forecasting there are several differences. While there have been studies of weather modification in the past, for the most part we think of weather forecasting as defining with observations what the atmosphere looks like at a particular time and then projecting forward for a few days what the atmosphere will look like. Climate projections are, however, mostly about how the forcing of the climate changes. Forcing? How is the energy budget being changed? What changes absorption and reflection? How does the surface change?

We often focus on how will the greenhouse gases like carbon dioxide change? While this is the most important global problem, when we think about what I will call large-scale adaptation, major energy projects that cover the Earth’s surface with windmills and solar panels, these land-use changes might be more important. And their importance might be in terms of local changes to the weather. Going back to the question posed at the beginning of this entry, benefits, risks, and liability for a specific project, I imagine the desire, the need, maybe even the requirement to do climate impact assessment studies.

Such an assessment study would necessarily be a set of model simulations with changes to the land-surface. There would need to be experiments designed to extract any possible signal from what is bound to be significant noise – variability within the system. New analysis techniques would be required. Given the need to evaluate specific projects, project designers would need access to and the ability to change climate models. This means that the ability to configure, run and evaluate climate simulations needs to exist outside of government laboratories and universities. Compared with weather forecasting, where we are pretty settled on the idea of collections of observations of the current state of the atmosphere, followed by prediction of the future, this is an enormous change. That is, there are few people who have the vested interest to want to play around on the insides of a weather model, but there are potentially many people with the interest and desire to play around with the insides of a climate model.

With this as introduction, the next articles will be a series on the challenges of how to address this potential need: the need for communities other than scientists to have access not just to the results from climate models, but the ability to configure climate models for particular changes to the Earth and investigate the impact of those changes.

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