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

Starlings are medium-sized passerine birds that are famous for gathering in huge flocks and moving across the sky in sync to form startling ‘murmurations’. Between October and February every year, millions of starlings migrate from northern Europe to Central and Southern Europe to escape the cold. But scientists have lately observed that warmer temperatures in northern European caused by climate change have shortened the starlings' stay in Southern parts. Studies have predicted that warmer temperatures could also make starlings advance their breeding period.

Though one would be fascinated by the sheer number of the birds in the flock (pre-roost murmurations have been known to number as many as 1,00,000 birds), many roosts are significantly smaller than they used to be due to population decline. Lack of food and habitat loss, partly driven by climate change, have put some of the starling species on the IUCN red list in various Europe countries. (IUCN- International Union for Conservation of Nature). Starlings are not alone in this struggle. Many birds around the world are impacted by climate change. The timing of bird’s migration, nesting, hatching, and feeding are adapted to specific conditions, such as the availability of suitable habitat and adequate food sources. These factors make birds particularly vulnerable.

Here is a closer look at the threats faced by birds due to a warming planet.

Migration pattern

The impact of climate change on birds migration patterns has been noticed in the last few decades. Scientists have documented that fewer birds show up in breeding and wintering grounds and they attribute it to the increasing temperatures, changing vegetation, and extreme weather conditions.

Birds synchronise their migratory movements with seasonal changes. The start of their journey and their speed must match the life cycle (before caterpillars pupate) of food sources at the stopover and destination sites. But these environmental cues go for a toss with changing climate.

Habitat loss

One of the major effects of climate change is the loss of habitats. While some species face shrinking ranges, others face habitat destruction. For migrating birds, flooding or desertification could spell doom. Flocks might fly thousands of kilometres only to find their destination submerged or barren. Many goose species use the Siberian tundra's rocky bedrock to raise their offspring. But increasing temperatures make the permafrost soil to thaw and change the habitat completely, making it impossible for the geese to breed.

Lack of food

A number of birds has adjusted breeding times to match early Spring. They arrive at the breeding site earlier than before.

Meanwhile, increasing temperatures also make the vegetation bloom and insects hatch earlier at the site. But sometimes these shifts are not in line with each other. As a result, the chicks hatch way after the caterpillars are gone. And so, they starve. (On average, the window of time when birds lay their eggs has gotten earlier by almost two weeks over half-a-century. Since many small songbirds can raise their young in roughly one month, two weeks is a big shift in their timing.)

Sea-level rise

Sea-level rise and erosion alter coastal wetlands. Many birds, such as piping plovers, that inhabit coastal areas lay their eggs directly on the sand of the beach in a shallow depression. The erosion of beaches and storm surges can cause nests to be lost to the ocean.

Smaller body, larger wings

A study published in December 2019 found that global warming was causing birds to shrink and their wingspans to grow in size. Scientists explained that it could be an adaptation of birds as smaller birds are better at cooling off, losing, body heat more quickly due to their larger surface-area-to-volume ratios. But smaller body size means less energy available for the birds to complete long journeys. Scientists say that birds would have evolved to grow long wings to compensate for their smaller bodies as it helps them survive migration.

Picture Credit : Google