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Climate Change in Boulder, CO

Annual Average Temperatures Show a Gradual Warming Trend? Take a second look!

The fitted trend line reveals a small but consistent increase in average annual temperature over time, with a slope of 0.0326 °F per year. That seems like a small increase however, if we look across the 100 years or so, we do see a significant increase in temperature. We also see year to year variability, especially in the 1930s, 1940s and the late 1990s. The R² value (0.0841) of the OLS regression also indicates that there is variability. However, just because temperatures have been fluxuating does not mean we should ignore the gradual increase in temperature the graph shows.

For example, we can calculate the total temperature change from 1893 to 2023 in Boulder, CO by taking the average temperature change by year (the slope of the trend line) and multiply that by the total number of years. The given slope is 0.0326 °F per year. For Boulder, CO we have temperature data from 1893 to 2023 or 130 years. If we take the slope of 0.0326 °F and multiply it by 130 years we get a total temperature change of 4.2 °F! Suddenly that gradual trend line looks a lot more serious. It is important to keep in mind that we only have temperature data from the last 130 years. If we had larger data modeled back through time we would see a much sharper increase (like with global averages).

Want to see the NCEI data used for this graph? You can download daily summaries for the Boulder, CO Station (USC00050848) here.