Climate Change to Boost Global Rainbow Rate

With apologies to Kermit the frog, there will likely be a lot more songs about rainbows by the year 2100.

According to a new study by researchers at the University of Hawai‘i (UH) at Mānoa, the average land location on Earth will experience about 5% more rainbows by the end of the 21st century. While it’s sensible to immediately blame rising leprechaun populations or unchecked use of the Care Bear Stare for an increase in this colorful phenomenon, the reality is a lot less amusing. Like other major changes in store for those living into the next century, the rate of rainbows will grow due to climate change.

“By 2100, climate change is likely to generate a 4.0–4.9% net increase in mean global annual rainbow-days (i.e., days with at least one rainbow), with the greatest change under the highest emission scenario,” the researchers write. “Around 21–34% of land areas will lose rainbow-days and 66–79% will gain rainbow-days, with rainbow gain hotspots mainly in high-latitude and high-elevation regions with smaller human populations.”

Using Flickr to Help Predict Future Rainbows

To estimate if rainbows might increase or decrease in a world altered by climate change, the research team decided to create a first-ever global map of their occurrences. For this, they turned to an unlikely ally: Flickr. As it turns out, the online photo sharing platform offers a deep well of data on rainbows, with millions of users uploading images of the atmospheric phenomenon from around the world. Of course, just typing in “rainbow” presented its own problem, as Flick does not limit corresponding hits to only natural rainbows.

“We had to sort through photos of rainbow artwork, rainbow flags, rainbow trout, rainbow eucalyptus, and rainbow foods to find the real rainbows,” co-author Amanda Wong said in a press release. 

Once they had a vast image collection of rainbows generated by the refraction of light by rain droplets, the research team trained a rainbow prediction model based on the rainbow photo locations and global maps of precipitation, cloud cover, and sun angle. The model was then applied to present and future rainbow occurrences over global land masses.

Not surprisingly, islands remain the reigning hotspots for rainbow activity. 

“Islands are the best places to view rainbows,” according to Steven Businger, study co-author and professor of atmospheric sciences at the UH Mānoa School of Ocean and Earth Science and Technology. “This is because island terrain lifts the air during daily sea breezes, producing localized showers surrounded by clear skies that let the sun in to produce majestic rainbows.”

What Will Change?

By 2100, the model predicts rainbow gains for northern latitudes and very high elevations where climate change is expected to bring warmer temperatures, less snow, and more rain. Regions where models show a drop in precipitation, such as the Mediterranean, are expected to lose rainbow days. 

While the team predicts that the average human will have more opportunities to witness a rainbow by 2100, they admit some uncertainty as to how regions dependent on rainbow activity for nature-based tourism or just overall mental well-being will adjust to a loss of average rainbow days.

“Climate change will generate pervasive changes across all aspects of the human experience on Earth,” lead study author Kimberly Carlson said in a release. “Shifts in intangible parts of our environment—such as sound and light—are part of these changes and deserve more attention from researchers.”