The 2021 Nobel Prize in Physics has been awarded to Syukuro Manabe, Klaus Hasselmann and Giorgio Parisi "for groundbreaking contributions to our understanding of complex physical systems," the Royal Swedish Academy of Sciences announced on Tuesday.

Syukuro Manabe and Klaus Hasselmann have been jointly awarded one half of the 2021 Nobel Prize in Physics "for the physical modelling of Earth's climate, quantifying variability and reliably predicting global warming."

Manabe showed how increasing CO2 in the air leads to increased temperature, which is basically how global warming works.

"His work laid the foundation for the development of current climate models," said the Nobel Prize in a tweet.

Additionally, Hasselmann found the method to prove that the extra CO2 in the air is produced by human activities.

Currently, in his 90s, Japan-born Manabe is working at Princeton University as a meteorologist.

Hasselmann is a German who retired as the scientific director of the German Climate Computer Center in Hamburg back in 1999. He now works at the Max Planck Institute for Meteorology.

Giorgio Parisi has been awarded the other half of the 2021 Nobel Prize in Physics "for the discovery of the interplay of disorder and fluctuations in physical systems from atomic to planetary scales."

Parisi, an Italian, now works at the Sapienza University of Rome.

In his speech during the press conference, Parisi expressed concerns over the current climate change situation.

"It's clear that for the future generation, we have to act now in a very fast way," he said.