Local Climate Change: Its Unique Causes and Effects

Global warming has always been a shaky term for me. It implies that there’s a one-dimensional effect of burning fossil fuels and that every place in the world is seeing the same trend. Climate change is a much more dynamic term that gets at the complexities of how humans interact with and alter the Earth’s systems. It also makes local changes in the climate more understandable, particularly if they're not what you'd expect. A recent talk I went to beautifully illustrates this point.

The presentation I saw was on the findings of a paper submitted to the Journal of Geophysical Research. The paper examines the effects of irrigation on global climate in the 20th century, and the results may surprise you.

The researchers found that temperatures around heavily irrigated areas actually showed significant summer cooling due to a variety of factors including evaporation and ground cover. The trend was particularly notable over the Indus Valley in India.

Areas downwind of irrigated regions also showed increased precipitation. Interestingly, the one exception was in India. This is due to technical dynamics related to the monsoon season to in-depth to explain here. The changes in temperature and precipitation also intensified in the latter part of the 20th century. This is due in part to the expansion of agricultural land and with it, irrigation.

It goes to show that though skeptics may be right when they say some places are cooling, they’re wrong when they say it disproves climate change. Greenhouse gases do have a global effect on the Earth’s atmosphere and climate. There are local factors that can override them, though, such as irrigation.

Michael Puma, the researcher from NASA who presented the findings, indicated that the effects of irrigation might be masking a warming trend in some of the regions. This could have major implications for future climate modeling. The science of modeling isn't perfect nor will it ever be. There are literally limitless inputs that could go into a model, and each one changes its outcome. For example, including the Empire State Building in a model could change wind patterns in the New York region, but it would have minimal impact on global modeling or a model for India. As the results from the study show, though including irrigation as an input for global and regional climate models could increase their accuracy and usefulness.

Forecasts using this information could benefit water managers and farmers in the affected regions. Cutting back on irrigation in water-stressed regions (which many irrigated areas are) could affect crop yields, crop types, energy usage, and planting times.  Having a sense of how and when these effects could play out would help people plan better and avoid negative impacts.

The full meaning of the results also shows the importance of using the term climate change. Global warming just doesn’t convey regional complexities nor does it allow decision makers to fully address local climate effects. Acknowledging the complex nature of the climate system is the key to getting the public to understand why not all trends are created equal. This understanding will help generate more public support for decision maker and individual actions that address climate change.

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