With nothing short of a wild winter hopefully soon behind us, we can start to look toward more time spent outdoors. But, as is typical in our region, the weather continues to toss us curveballs. Last week saw above-average temperatures that melted much of the massive snowpack that remains in the foothills and above.  

Naturally, area rivers are rising, which prompted the National Weather Service to issue a Flood Watch for much of northern Nevada. 

This isn’t unusual for the season, but there was one notable difference last week: higher nighttime temperatures. That leads to higher amounts of snow melting more quickly. After a tumultuous winter across the region, some may be wondering how all of this weather is impacted by climate change.

Enter a new tool, the Climate Shift Index.

“The climate shift index compares how often a given temperature will occur in our current climate with the frequency of that temperature without global warming, ” the Director of Climate Science at Climate Central Dr. Andrew Pershing explained in a video on the tool’s website. 

The Climate Shift Index is a data-driven, science-backed tool that shows how climate change influences daily temperatures. In essence, the index quantifies, on a relatable scale, just how much climate change is responsible for warming and cooling events. Pershing further explained that this tool allows users to see the direct fingerprint of climate change. 

Scientists at Climate Central use two models to develop the index, which ranges from negative five to positive five. Any positive factor indicates a heating event that is more likely caused by climate change. For example, the Climate Shift Index places Reno at a four for April 29. That means this warming event is about four times more likely due to climate change; conditions that would be extremely unlikely without human carbon emissions.

The scale was built to work with temperatures that are observed most often. It is defined as the ratio of how likely a temperature is in today’s shifted climate compared to how likely the temperatures would be without anthropogenic climate change. Climate Central has found that positive value days occur more frequently than negative value days. This collaborates almost seamlessly with the rise in global mean temperature. A negative value indicates that cooler days are less likely under current climatic conditions. For example, a daily index reading of negative two means the temperature is two times less likely due to climate change.

This Climate Shift Index can be generated for any current day with a four-day outlook and provides meteorologists with a tool to help the public understand the impact of climate change on daily weather.

The data is created through two methods that are averaged together for the final index. The first method compares 22 climate models that are run with and without human greenhouse gas emissions. This provides a baseline of what the temperatures would be if the climate was not warming. The second method, which is based on historical observations, calculates the frequency of daily temperatures over the past three decades. Temperature change for a given location is calculated in relation to the increase in global mean temperature. This data point helps quantify just how much human-caused climate change has contributed to the rise in global mean temperature. 

Based on the average temperature of the last 50+ years, Reno is one of the fastest-warming cities in the country.

This story was originally published with the Sierra Nevada Ally.