New Delhi: Cosmic rays from supernovae – or exploding stars – can influence Earth’s cloud cover and its climate, scientists have foundfor the first time.

Conducted by Dr. HenrikSvensmark, from DTU Space, senior researcher Martin BødkerEnghoff, from DTU Space, Professor NirShaviv at the Hebrew University of Jerusalem, and Ph.D. student Jacob Svensmark at the University of Copenhagen in Denmark; the study claimed that the discovery helped fill in a mysterious gap in our knowledge of our climate and may help to explain unusual periods of warmth and cold during the past 2,000 years.

Scientists call this new discoveries 'a breakthrough' in the clear understanding of how the cosmic rays from supernovae can influence Earth´s cloud cover and thereby climate on Earth.

According to them; Cosmic rays knock electrons out of air molecules, forming ions that attract liquid water droplets to form aerosols, which condense into clouds. With increasing cosmic rays over the Earth, more ions, aerosols, and clouds are formed, which then cool the planet with more rain.

The Study Findings in Detail:
The study explains in detail how atmospheric ions, helps the growth and formation of cloud condensation nuclei -- the seeds necessary for forming clouds in the atmosphere.

It stated that, when the ionization in the atmosphere changes, the number of cloud condensation nuclei changes affecting the properties of clouds. More cloud condensation nuclei mean more clouds and a colder climate, and vice versa. Since clouds are essential for the amount of Solar energy reaching the surface of Earth the implications can be significant for our understanding of why climate has varied in the past and also for future climate changes.

Cloud condensation nuclei can be formed by the growth of small molecular clusters called aerosols. 

This is definitely a change in the understanding of how cosmic rays affect climate on Earth because until now it has been assumed that additional small aerosols would not grow and become cloud condensation nuclei, since no mechanism was known to achieve this. 

But, with this study, the new results reveal; both theoretically and experimentally, how interactions between ions and aerosols can accelerate the growth by adding material to the small aerosols and thereby help them survive to become cloud condensation nuclei. It gives a physical foundation to the large body of empirical evidence showing that solar activity plays a role in variations in Earth's climate.

For the clear understanding, the scientists cited few examples like; the Medieval Warm Period around year 1000 AD and the cold period in the Little Ice Age 1300-1900 AD.

HenrikSvensmark who is the lead author of the new Nature-study said, “It gives a physical foundation to the large body of empirical evidence showing that solar activity plays a role in variations in Earth’s climate. For example, the Medieval Warm Period around year 1000 AD and the cold period in the Little Ice Age 1300-1900 AD both fit with changes in solar activity.” 

2 years and 3100 hours of testing
For the study, the researchers looked into the effects of cosmic rays on a simulation of Earth's atmosphere, which was recreated inside a cloud chamber -- a sealed lab which mirrors the pressure and moisture of the upper atmosphere, a publication reported.

Data was taken over a period of 2 years with total 3100 hours of data sampling. The experiments were repeated up to 100 times in order to obtain a good signal relative to unwanted fluctuations. And, then the results of the experiments agreed with the theoretical predictions.           

“Finally we may have the last piece of the puzzle explaining how particles from space affect climate on Earth,” said study co-author Martin BødkerEnghoff from DTU Space.

“It gives an understanding of how changes caused by solar activity or by super nova activity can affect climate.” 
The finding of the study waspublished in the journal Nature Communications. 

The hypothesis of the Study in a nutshell:

• Cosmic rays, high-energy particles raining down from exploded stars, knock electrons out of air molecules. This produces ions, that is, positive and negative molecules in the atmosphere.

• The ions help aerosols -- clusters of mainly sulphuric acid and water molecules -- to form and become stable against evaporation. This process is called nucleation. The small aerosols need to grow nearly a million times in mass in order to have an effect on clouds.

• The second role of ions is that they accelerate the growth of the small aerosols into cloud condensation nuclei -- seeds on which liquid water droplets form to make clouds. The more ions the more aerosols become cloud condensation nuclei. It is this second property of ions which is the new result published in Nature Communications.

• Low clouds made with liquid water droplets cool the Earth's surface.

• Variations in the Sun's magnetic activity alter the influx of cosmic rays to the Earth.

• When the Sun is lazy, magnetically speaking, there are more cosmic rays and more low clouds, and the world is cooler.

• When the Sun is active fewer cosmic rays reach the Earth and, with fewer low clouds, the world warms up.

The implication of the study suggests that the mechanism can have affected:

• The climate changes observed during the 20th century

• The cooling’s and warming’s of around 2oC that have occurred repeatedly over the past 10,000 years, as the Sun's activity and the cosmic ray influx have varied.

• The much larger variations of up to 10oC occurring as the Sun and Earth travel through the Galaxy visiting regions with varying numbers of exploding stars.

References:
https://www.inshorts.com
https://www.sciencedaily.com
http://www.space.dtu.dk
https://www.eurekalert.org
http://indianexpress.com