WHAT WAS CLAIMED
An established scientific theory shows a key driver of climate change is impossible.
OUR VERDICT
False. Experts say the theory does not disprove climate change, and has been misunderstood.
AAP FACTCHECK - A graphic being shared on social media falsely claims a scientific theory about the way gases behave is incompatible with a key driver of human-induced climate change.
Experts say the post misunderstands the scientific law that it cites, and that there's been a drastic increase in the amount of greenhouse gases in the atmosphere as global temperatures continue to rise.
The false claim is made in a Facebook post with a two-part graphic featuring an illustration of a cow dressed in a lab coat, with text on the graphic stating "there's no CO2 [carbon dioxide] or CH4 [methane] positive feedback loop".
"According to ideal gas law, as temperatures rise, air expands, density thins, and absorption drops … science says chill," text at the bottom of the graphic says.
Ideal gas law is a well-established scientific theory that describes how gases behave under different conditions. It's used by scientists to measure how the properties of gases - such as temperature, pressure and volume - change in relation to each other.
The way gases behave in the atmosphere is a key part of understanding climate change, with decades of scientific evidence showing rising emissions of gases, including carbon dioxide and methane, are driving increasing global temperatures.
These greenhouse gases absorb heat that would otherwise exit the atmosphere and reflect it back to earth.
The absorption of heat by greenhouse gases is a natural feature of the atmosphere, but over the past century a drastic increase in emissions of these gases has caused this heating effect to accelerate.
Scientific evidence shows the acceleration of this heating effect will worsen due to what are called positive feedback loops.
This describes what happens when a change in the climate triggers effects that accelerate more warming. For example, when soil that has been frozen for hundreds or thousands of years thaws, it releases stored carbon dioxide and methane into the atmosphere.
This increases greenhouse gas concentrations, trapping more heat and further warming the earth, which causes even more thawing and gas release.
The Facebook post claims ideal gas law shows these loops can't happen because as temperatures rise, the air expands and the density of the gas thins.
As a result, the post claims, this actually reduces the absorption of heat - contrary to the understanding of the greenhouse effect.
Robyn Schofield, an atmospheric chemist at the University of Melbourne, said the post misunderstands ideal gas law and conflates it with the greenhouse gas effect.
She said a rise in temperature does lead to a slight increase in the size of the atmosphere - the layer of gases and vapour surrounding the earth.
However, while increasing temperature causes the gases to spread out more, it doesn't follow that the absorption of heat decreases, as the post claims.
Since the molecules themselves absorb heat, the heating effect remains unchanged, she said.
"The [greenhouse gas] molecules haven't disappeared," she told AAP FactCheck.
However, the concentration of greenhouse gases in the atmosphere has increased substantially over the past century, and this has significantly increased heat absorption.
Martin Jucker, a physicist at the University of New South Wales, said the rise in the amount of methane in the atmosphere since 1750 is more than 500 times greater than any expansion of air due to a small temperature rise, according to ideal gas law.
"Methane has increased by 162 per cent, which means its concentration has increased … 540 times more than the density would have decreased," Professor Jucker told AAP FactCheck.
Zoran Ritsovski, a physics professor at Queensland University of Technology, agreed that the key factor is the concentration of greenhouse gases, not the density of molecules.
"Any decrease in density resulting from higher temperatures is SIGNIFICANTLY more than offset by the much larger influence of methane and CO2 on the temperature of the atmosphere," he told AAP FactCheck.
AAP FactCheck is an accredited member of the International Fact-Checking Network. To keep up with our latest fact checks, follow us on Facebook, Instagram, Threads, X, BlueSky, TikTok and YouTube.
