My Science School

We often come across stories about how extreme weather events are affecting the planet's inhabitants. We keep learning about how they impact a specific ecosystem or a species in some corner of the world and in ways nobody can foresee. Recently in the news for this is the iguana.

This January, South Florida experienced unusually cold temperatures. At one point, it even reached -3 degrees Celsius, making it among the lowest since 2010. Days before the region plunged into cold weather, the National Weather Service warned residents about the impending weather change. It also alerted them to look out for iguanas falling off trees in the area. What do low temperatures have to do with falling iguanas?

As cold-blooded reptiles, iguanas rely on the sun to keep them warm and their body functioning properly. But neither can happen when snow falls or the temperature drops really low, say below 4 degrees Celsius. When it becomes unbearably cold for these reptiles, they climb trees hoping to stay safe up there till it gets warmer. But what happens is, without the warmth, they cannot move because their body does not function well. So, they enter a state of sleep called torpor, which is almost like a coma. And that's when they lose their grip and fall off the trees. Once temperatures go up (above 10 degrees Celsius), these creatures thaw out and get back to the life that once was.

This is not the first time this phenomenon has occurred - it was reported in 2018 and 2020 too. But when low temperatures continue for a longer period of time, it may prove to be fatal for these creatures.

Picture Credit : Google

The United Arab Emirates (UAE) has a desert climate, characterised by mild winters and very hot summers. The humidity of the Persian Gulf makes the heat unbearable. It records an average rainfall of 100 mm every year. However, in recent years, the intensity of rainfall has gradually increased in the country. This is credited to the cloud seeding operations undertaken by its meteorological department. It is not just the UAE, even India. China and many other countries use this weather modification procedure to cause rain or to increase its intensity to address drought and water shortage. It is also used to control air pollution and to cause snow.

Cloud seeding is an attempt at inducing moisture in the clouds to generate rain. It involves use of chemicals that target rain-bearing clouds above a catchment area such as a river, reservoir or a lake. The chemical agents are dispersed in clouds using either aircraft or by ground-based dispersion devices that use rockets or guns to fire canisters of chemicals Sodium chloride (common salt), silver iodide, potassium iodide and dry ice (solid carbon dioxide) are some of the chemicals used. The cloud seeding missions are not constrained by seasons and are carried out throughout the year when seedable clouds are detected.

How does it work?

You may be aware of the evaporation process, which is an essential part of the water cycle. The sun drives evaporation of water from oceans, lakes and even moisture from the soil. The water molecules escape and form water vapour. The vapour remains in the atmosphere until it condenses to form raindrops, ice crystals and then into clouds. That is, clouds form when supercooled water vapour condenses and then freezes onto particles, called ice nuclei. Over time, the droplets and crystals that make up a cloud can attract more water to themselves. When water droplets grow heavy enough, gravity pulls them down as raindrops.

In the seeding process

As mentioned earlier, in the cloud seeding process chemicals that can aid precipitation are seeded (dispersed) into rain-bearing clouds. When these particles meet moisture in the clouds, they act as artificial ice nuclei and trigger the formation of more ice crystals and raindrops. The deficit in moisture content could be made up by using hygroscopic (water absorbing) material such as common salt.

Picture Credit : Google