What Climate Models Tell Us About Future Global Precipitation Patterns
By: Madison Hunter
Tags: Climate Change, Technology, Environment, Future, Science

What are climate models?

As described by the Geophysical Fluid Dynamics Laboratory, climate models are mathematical representations of the major components of the climate system (the atmosphere, land surface, ocean, and sea ice) and their interactions. Each component of the climate models are described as such:

The atmospheric component simulates clouds and aerosols and plays a large role in the transport of heat and water around the globe.

The land surface component simulates surface characteristics such as vegetation, snow cover, soil water, rivers, and carbon storage.

The ocean component simulates ocean current movement and mixing. It also simulates biogeochemistry because the ocean is the dominant reservoir of heat and carbon in the whole climate system.

The sea ice component modulates solar radiation absorption (the albedo of the planet) and air-sea heat and water exchanges.

All climate models may contain and track different components. However, an article by the University at Albany explains that the atmosphere, hydrosphere, biosphere, cryosphere (ice-covered regions, includes ground in permafrost), and lithosphere (upper layer of Earth’s crust, both continental and oceanic), are the main drivers of climate change and are all generally represented to some extent or another in most climate models to ensure accurate simulations.

How do climate models work?

Climate models divide the Earth’s surface into a three-dimensional grid. Each grid contains equations that represent each component of the model. Therefore, there are atmospheric equations, hydrospheric equations, lithospheric equations, and so on. These equations represent how each component of the climate works in a given area for a given set of variables. These variables represent different conditions and changes to those conditions. Variables may either be calculated by the equation or may be parameterized (hard-coding the variable to save on computing power).

Because there are so many equations and variables at play, a lot of computing power is required to run the system. In other words, the smaller the individual cells of the grid, the more complex and detailed the model, the more computing power is required.

Climate models also include the element of time, which allows models to simulate climatic conditions over a range of time units. These complex mathematical equations which describe how the different components of the atmosphere interact, and within themselves, how the materials within these components interact, give scientists the ability to “look into the future” to see what the climate will be like decades into the future.

Currently, there are three types of climate models: energy balance models, intermediate complexity models, and general circulation models.

Energy balance models forecast climate change as a result of Earth’s energy budget. This type of model looks specifically at how surface temperatures are affected by solar energy and Earth’s natural reflectivity (albedo). Using this type of model, scientists use equations that represent the exchange of energy between Earth and the Sun to better determine how heat is stored on Earth.

Intermediate complexity models share similarities with energy balance models although they include Earth’s biogeochemical components to better simulate large-scale climate scenarios. Scenarios such as glacial melting, changes in ocean currents, and changes in greenhouse gas emission composition of the atmosphere can be simulated to determine how they affect Earth’s climate on the whole.

Finally, global circulation models are the most complex, time-intensive, and computing-heavy models that offer precise predictions about climate change. These models incorporate each component listed above, including equations concerning chemistry, the carbon cycle, and the makeup of isolated areas. This type of model would use a small three-dimensional grid which offers more precision when it comes to understanding how these grids interact with each other.

The difficulty of predicting precipitation changes with climate models.

A chapter discussing the evaluation of climate models published by the Intergovernmental Panel on Climate Change (IPCC) discusses how the modeling of large-scale future precipitation patterns has improved since the days of the AR4 (the IPCC’s fourth climate assessment report conducted in 2007), although the modeling of regional precipitation remains subpar. According to their studies, the IPCC has found that climate models are prone to underestimating the sensitivity of extreme precipitation events to changes in global temperature. This implies that models could underestimate the projected increase in extreme precipitation events in the future.

The chapter goes on to discuss how the simulation of precipitation is one of the most rigorous tests a model can conduct because precipitation characteristics depend heavily on various other processes (such as cloud formation, radiation, atmospheric moisture, and aerosols) that must be parameterized (the processes are defined by a specific variable in the code instead of letting the model calculate the value of the variable itself — saves on computing power when dealing with processes that can occur over much shorter scales than an entire grid cell) in the model. In some cases, where precipitation is concerned, this parameterization of variables must include a range of values to better account for variations in the cell in question, such as topography.

In other words, due to the ranges of error involved in modeling precipitation, there can be varying levels of certainty when predicting the future precipitation of a region. This results in studies having to use several estimations of future precipitation to draw somewhat solid conclusions that may end up being changed a few years down the road. Because of this variation in the regional results of different models (one model could say that a region will become wetter while another model will say that the same region will become drier), a multimodel mean is required to get a rough answer to questions concerning the future of precipitation patterns.

What climate models tell us about future global precipitation patterns.

Without using precipitation-focused climate models, scientists can already infer a couple of things about how precipitation will change in response to a warming climate.

According to a paper published by the National Center for Atmospheric Research, increased planet temperatures would give rise to increased evaporation and, as a result, desertification. Greater evaporation would contribute to the severity and duration of droughts. As the planet warms, the atmosphere’s carrying capacity for water also increases. This, coupled with increased evaporation, means that storms, whether they be thunderstorms, cyclones, or hurricanes, will unleash even greater amounts of precipitation. Vast amounts of precipitation that fall on parched ground will find it hard to be absorbed, resulting in greater amounts of runoff and severe flooding events.

The article goes on to mention how climate models suggest that dry areas will become drier, and wet areas will become wetter, due to a lack of change in the planet’s wind patterns as forecasted for the foreseeable future. This means that while copious amounts of water will be added to the atmosphere, its distribution as precipitation will be uneven.

When it comes to making predictions using climate models, the results generally mirror the phenomena described above. As previously discussed, a model mean is generally required to get the average prediction about future precipitation levels for a given region. However, there are some parts of the world where 9 out of 10 models will agree about future precipitation patterns. Currently, models agree that tropical and high latitude regions will see an increase in precipitation. Models predict that locations such as India, Bangladesh, Myanmar, and northern China will observe greater amounts of precipitation. Regions that will likely see drier conditions include the Mediterranean, southern Africa, and parts of Australia and South America. North America, Europe, and the greater part of northern continental Asia appear to be slightly harder to predict due to seasonal variation, with precipitation prediction amounts being on the higher end during the winter, spring, and fall and predicted precipitation amounts being lower during the summer months.

Regardless of regions becoming wetter or drier, a consensus among climate models suggests that intense precipitation events will increase worldwide by the end of the century. It’s currently projected that a particular intensification of precipitation events will occur in Eurasia and North America.