An Idiot’s Guide to Climate Projections

This year’s Climate and Society class is out in the field (or lab or office) completing a summer internship or thesis. They’ll be documenting their experiences one blog post at a time. Read on to see what they’re up to.

By Colin Gannon, Climate and Society 2014

In the last few years, you’ve probably come across some dire warnings about the future climate of your hometown. Maybe it was that downtown would be submerged by 2050, or that extended droughts would become the norm.

Where do these projections come from?

Many published projections* about future climate can be traced back to the Intergovernmental Panel on Climate Change (IPCC), which releases massive assessments that summarize scientific literature written by top climate scientists. These reports go to great efforts to say something about what the world will look like 10, 20, or 80 years from now.

And that’s where climate modeling comes in. In climatology, modeling is basically an attempt to predict climatic conditions at a given time. The best models analyze hundreds of components of the climate system from Pacific Ocean temperatures to ice on Greenland to greenhouse gases in the atmosphere and their interactions with each other.

This is a very complex task, and an inherently imperfect art. Fortunately, the best meteorological institutions around the world produce their own models and use various methods to simulate global climate. NASA has a few, as does the UK Met Office; China and Japan also have highly successful models of their own. As a result, there are many slightly different global climate models.

A visual representation of a NASA model, which simulates the interaction of winds and airborne particles, like dust and sea salt. These are two of the many variables that would go into a climate model. Source: NASA/Goddard Space Flight Center.

Each individual model may be subject to minor flaws in its design, perhaps because it over-estimated the cooling effect of clouds or didn’t quite get El Niño right. The good news is that those pitfalls are often made up for in another model. By taking a bunch of models, setting key variables (like the rate of greenhouse gas emissions) to be the same for each, and then averaging the results, we get a more accurate simulation of the climate. One program that does exactly this is the Coupled Model Intercomparison Project (CMIP5), the source of the IPCC’s projections.

The beauty of CMIP5 is that all of its results are available to researchers, opening the door for virtually any region in the world to receive custom, tailored climate projections. So while the IPCC does its own analysis, institutions like the Red Cross/Red Crescent Climate Centre can use the same data, zooming in to areas of interest. In this way, farmers in Zambia can get information they need, like the number of dry days during future harvest seasons. Really any climate-related information through 2100 can be projected using the CMIP5 models.

As time goes on, scientists will get better at simulating the climate, and model projections will become more accurate. It might just be a little unnerving to know exactly what our planet will look like a few decades from now.

*There are two approaches to climate modeling, each with its own strengths and weaknesses. The one discussed here is dynamical modeling, meaning physical equations are used to simulate the Earth’s systems. The other method, statistical modeling, extrapolates recorded observations to predict conditions.

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