New research has made the ‘human fingerprint’ on climate change clearer as it points to how increase in carbon dioxide levels in the upper-stratosphere layer have altered the planet's atmosphere structure.

How is a 'human fingerprint' recognised?

First, let us understand how exactly is the ‘human fingerprint’ recognised in such a scenario? The Earth's atmosphere has five major layers:

Troposphere: That goes up to 12 km from the Earth's surface.

Stratosphere: Approximately 12-50 km from the surface of the Earth.

Mesosphere: Located between 50-80 km of the Earth's surface.

Thermosphere: Located between 80-700 km above the surface of the Earth.

Exosphere: Situated around 700-10,000 km from the surface of the planet

The differences between the temperatures of the troposphere and lower stratosphere have often been recognised as the ‘human fingerprint’ on climate. However, this has not included information from the mid- to upper-stratosphere (25-50 km above the surface of the Earth).

Also Read: Rice and maize crops adapting to temperature changes but not wheat: Study

Detecting 'human fingerprints' in climate change in the stratosphere

The stratosphere is often termed as the home of the planet's ozone layer that gives protection from the harmful ultraviolet (UV) radiation of the Sun. The layer is also the maximum till where jet planes can fly.

Including the information from the mid- to upper-stratosphere will improve the detectability of a human fingerprint on climate change by a factor of five, stated a write-up published in the Proceedings of the National Academy of Sciences. "Enhanced detectability occurs because the mid- to upper-stratosphere has a large cooling signal from human-caused carbon dioxide increase, small noise levels of natural internal variability and differing signal and noise patterns. Extending fingerprinting to the upper stratosphere with long temperature records and improved climate models means it is virtually impossible for natural causes to explain satellite-measured trends in the atmosphere's earth structure," the journal write-up added.

Noise in the troposphere can comprise daily weather, inter-annual variability because of El Nino and La Nina as well longer natural fluctuations in climate. However, in the upper stratosphere, the variability noise is smaller and the climate change signal caused by humans is larger, hence more easy to distinguish.

'Claims that climate change is natural are incorrect'

Lead author of the study Benjamin Santer said this is the clearest evidence of a signal of human-caused climate change, associated with increases in carbon dioxide.

Also Read: Climate change could reduce life in the ocean's twilight zone by up to 40%, says new study

Santer added that the research rebuts claims that recent temperature changes in the atmosphere and Earth's surface are natural, either due to the Sun or any internal cycles present in the climate system. "A natural explanation is virtually impossible in terms of what we are looking at here: changes in the temperature structure of the atmosphere. This research puts to rest incorrect claims that we don’t need to treat climate change seriously because it is all natural," Santer was quoted as saying in a blog post on the Woods Hole Oceanographic Institution's website. Santer is an adjunct scientist at the institute in Massachusetts.

Inspiration from previous studies

The research was inspired by the earlier works of Richard Wetherald and Suki Manabe, who in 1967 studied how carbon dioxide generated from the burning of fossil fuel might change the temperature in the atmosphere. The simple climate model used by the researchers found that rise in carbon dioxide levels led to more heat being trapped in the troposphere and less of it escaping higher up in the stratosphere, hence, keeping the troposphere warm and the stratosphere cool. This premise has been confirmed by other studies as well. However, they did not look at the climate change patterns in detail in the mid- to upper-stratosphere layer.

The new research looks for climate change patterns caused by humans — also called 'fingerprints’ — in the mid and upper-stratosphere.

The institute's blog also quoted co-author Qiang Fu as saying the human fingerprints in temperature changes in the mid- to upper-stratosphere layer because of rise in carbon dioxide are "truly (an) exception because they are so large and so different from temperature changes there due to internal variability and natural external forcing." Fu added that these unique fingerprints enable the detection of the human impact on climate change because of carbon dioxide in a short period (10-15 years) with high confidence.

Also Read: Explained: What is carbon, capture, utilisation, storage and can it help transition to net zero emissions

(Edited by : Shoma Bhattacharjee)