A Range of Possible Future Climates

We recommend that Hoosiers prepare for a range of possible future climatic conditions.

The future outlook in this report is based on climate models, which are mathematical representations of Earth’s climate system based on hundreds of thousands of lines of computer code (or more). Many different research groups around the world have made different models, and these models have been continuously improved over the last several decades.

Even with sophisticated tools like these, no one can predict the future climate with total certainty for a variety of reasons. First, we do not know how people’s actions will affect concentrations of heat-trapping gases in the future. Second, there are small chances of unpredictable natural events, such as the eruption of volcanoes. These events affect climate, but are beyond the control of climate scientists.

However, researchers can use climate models to make “projections” of future climate based on reasonable assumptions about future atmospheric conditions. The projections used in this report assume that society will continue to release heat-trapping gases at “medium” or “high” rates.

Even when one of these assumptions is used, responsible scientific projections will still suggest a range of possible future climates. While the models are impressive in their ability to simulate past climates, they do not – and cannot – perfectly represent the enormously complex natural world.

Each of the different models attempts to balance simplicity (to allow faster computations) with complexity (to simulate the most important aspects of the climate system). The various models strike different balances, using different mathematical equations to represent the processes related to climate. These models necessarily depict simplified versions of the world and give somewhat different projections for the future, even when given the same set of assumptions about heat-trapping gases in the atmosphere. For instance, some models depict faster warming than others. Scientists have the most confidence in future projections when many different models produce similar results based on the same set of assumptions.

In creating this outlook for Indiana’s climate, we wanted to provide the public with projections that could differentiate future conditions in different parts of the state. Hoosiers know that Indiana’s climate is different from north to south, but today’s global climate models have relatively low spatial resolution, meaning they may not show patterns like this. To produce more useful results at the state level, we used a procedure called “statistical downscaling” to translate the low-resolution results of the climate model to higher-resolution estimates within a small region. This technique is commonly used and provides the advantage of producing more realistic patterns of climate projections across the state. Of course, this technique also relies on a set of assumptions itself. The performance of downscaling techniques is tested and improved based on past data, but can never be perfect.

The outlook for Indiana’s future climate presented in this report relies on projections from 10 global climate models. These projections have been downscaled and analyzed to show how the future climate is likely to vary across the state. For any given time point and emissions level, we interpret the average value across the different models as the most likely future outcome.

However, to fully understand the projections in this report and use them in planning, it is important that readers not only note the main numbers presented, which are typically averages of the projections from the 10 different models, but also the range of results produced by the different models. This gives some indication of the level of agreement among models that a given change will happen.

For instance, in this report, all models suggest that Indiana’s climate will become warmer in all seasons, and that this warming will increase over time. In addition, most or all of the models suggest Indiana’s winter and spring months will become substantially wetter over time. The consistency of these results across models gives us high confidence in these specific projections.

However, we have less confidence in some of the other projections, such as changes in precipitation during the summer and fall months. During this period, some models suggest minor increases in precipitation while others suggest large decreases. For any given variable, it is useful to understand both the most likely future outcome and the range of possibilities suggested by the different models.

Planning now for a range of possible future climates will be much less risky than counting on one particular outcome.