Climate change could bring us more rainbows, but that's not a good thing

Have you ever wondered how rainbows are formed? These bands of light that we usually associate with positive things like happiness or good weather, appear with torrential rains and floods. That is why they are a meteorological rarity that only a lucky few get to see after a dark day.

But soon rainbows could become commonplace due to climate change.

Researchers at the University of Hawaii estimate that in about 77 years, by 2100, we will have more rainbow days. This is because global warming will modify the behaviour of precipitation, creating the perfect rainy scenario to refract sunlight.

On average, climate change could bring us more rainbows in the future. But that won't be as pretty as it seems, according to data from a new study by US researchers. So we will have more rainbows in the future, but these will not bring good news.

How is the rainbow formed?

Rainbows form when the sun breaks through the clouds while it rains or immediately after. In both cases, the atmosphere is still loaded with water droplets, which act as prisms, breaking the light of the sun's rays that fall on them.

Thus, what is initially white light breaks down into all those colours that we see in the form of an arc. Although it is not really an arc, a circle. What happens is that you can't see the bottom part because of the interference of the horizon.

From ground level, it can only be seen under solar angles between 0° and 42°, which occur in the early morning or late afternoon. Also, ideally, there shouldn't be too many clouds that can block sunlight.

In addition, of course, it also has to rain. These liquid precipitations are what facilitate the refraction of light, so it is clear that climate change must influence it in some way.

Link between rainbows and climate?

To carry out this study, published in Global Environmental Change, its authors developed a database made up of photographs of rainbows from around the world and various sources. Afterwards, they trained an empirical model on the occurrence of this phenomenon and tested it both with the current climate and with three future climate scenarios. 

Thus, they saw that, currently, on Earth, there are an average of 117 ± 71 days per year with suitable conditions for the rainbow. However, it is likely that by 2011 this average will increase between 4% and 4.9%. Although this would not be distributed evenly. In fact, between 21% and 34% of land areas would lose rainbow days. On the other hand, between 66% and 79% would experience this increase.

To refract sunlight, the atmosphere must be moist and laden with water droplets. In addition, the idea is that there are not too many clouds that can block the light since the Sun must hit directly on the drops to produce the rainbow. Something that usually happens during the morning or late afternoon, when the Sun is between 0° and 45° degrees.

If these three conditions are not met, no rainbow will occur. This is why we only see these arcs of light when there is heavy liquid precipitation.

• In the 20th century, rainbows were almost a myth since there were no torrential rains, but climate change changed that.

• There are now hundreds of photos of rainbows, and by 2100 we'll see, even more, the researchers say. They used this photographic material to create a weather model that estimated the appearance of rainbows in the future.

• It was thanks to this that they saw that the average of 117 to 71 rainbows per year would increase between 4% and 4.9% in 2100.

More rainbows in some places on Earth

In the future, the planet's hottest poles will have more rainbows per year. By this, we mean Alaska, Norway, the Korean Peninsula, Japan, the Tibetan Plateau, and eastern Borneo.

Researchers believe that these areas will have more rainbows because climate change will bring less snow and more rain to the region. While more stable places, such as the Mediterranean, South America, Australia and Africa will experience the opposite effect: they will have fewer rainbows in the year 2100.

Rainbows are the result of meteorological precipitation, but they can be used as indicators to predict some catastrophes:

• A decrease in rainbows in a region, for example, implies more droughts, since rainfall is estimated to be low.

• On the other hand, an excessive increase of the rainbow in a region could indicate the appearance of torrential rains or floods.

These are all guesses, of course, based on the possible climate scenarios proposed by the researchers. But what is clear is that, if we do not take action, in the coming year's everything will change: we will have more rainbows and more alarming climate changes on the planet.

It can also affect psychologically.

In addition to its relationship with rainfall, this could have psychological consequences. And it is that, according to the authors, the rainbow usually causes well-being and a connection with nature.

However, with these new scenarios, the conception that humans have of this phenomenon could change. For example, if it is linked to torrential rain and flooding, it could no longer be seen as a positive thing. And, on the other hand, those who will see them less and less will miss that connection with the nature of yesteryear.

These are all assumptions, which would require a psychological analysis of the data. However, what is clear is that, if we do not act, in the next year everything will change. And maybe even what before could only be related to positivity and good vibes, ends up becoming something terrifying.

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