WHAT WAS CLAIMED

There is no evidence carbon dioxide directly causes any change in the climate.

OUR VERDICT

False. Numerous scientific bodies and studies have found an increase in CO2 in the atmosphere has changed the climate.

One Nation senator Malcolm Roberts claims there is "no empirical evidence that directly links CO2 as the direct cause of any change in climate".

A page on the senator's website titled, Climate Fraud, says there is no "scientific justification" for government policy that reduces carbon dioxide output. "I know there is no valid scientific data proving cause-and-effect from human carbon dioxide and temperature increases," he claims.

The Queensland senator's assertion is false and ignores decades of climate research including empirical observations of surface and ocean temperatures. He denies human activity is affecting the climate, but declined to produce evidence supporting his claim.

The Intergovernmental Panel on Climate Change (IPCC), a United Nations body, estimates human activities have caused about 1°C of global warming above pre-industrial levels, with a likely range of 0.8°C to 1.3°C.

"The continued growth of atmospheric CO2 concentrations over the industrial era is unequivocally due to emissions from human activities," the latest IPCC report concludes.

It says this human influence has warmed the atmosphere, ocean and land, which have together taken up "a near-constant proportion of CO2 emissions from human activities over the past six decades".

The report notes CO2 concentrations have continued to increase in the atmosphere since 2011, reaching annual averages of 410 parts per million for carbon dioxide.

A 2020 article on the US National Oceanic and Atmospheric Administration (NOAA ) website said over the past 60 years CO2 levels had increased about 100 times faster than during previous natural increases, and this was "mostly because of the fossil fuels that people are burning for energy".

The Global Carbon Project, a partner of the World Climate Research Programme, which provides research to underpin the UN Framework Convention on Climate Change, found global carbon dioxide emissions rose about 4.3 per cent in 2021 from the previous year.

The latest figures from NASA show atmospheric CO2 levels reached 418 parts per million (ppm) in January this year, the highest level in at least 800,000 years. The US space agency states human activities have profoundly increased carbon dioxide levels in Earth's atmosphere.

Dozens of sites around the world collate regular direct measurements of CO2 levels, including the Mauna Loa Observatory in Hawaii, which has the longest record with measurements dating back to 1958. Earlier records of CO2 levels have been developed from ice cores, which contain trapped air bubbles providing a record dating back 800,000 years.

Australia's national science agency the CSIRO says carbon dioxide is the "most significant greenhouse gas" contributing to human-induced global warming. The agency's State of the Climate 2020 report details how cumulative emissions of CO2 will determine the "speed and magnitude of global mean surface warming during this century and beyond" (page 18).

The Australian Academy of Science attributes climatic temperature changes to six causes. Two (solar fluctuations and volcanic eruptions) are "entirely natural", while the other four are predominantly caused by human influences (increases in atmospheric CO2 and other long-lived greenhouse gases; increases in short-lived greenhouse gases; changes to land cover and increases in aerosols).

Climate scientists told AAP FactCheck that Senator Roberts' claim is not credible given the overwhelming weight of evidence.

"There is a whole field of climate science known as 'detection and attribution' which is precisely aimed at identifying observed climate changes that would be unusual or impossible due to natural variability alone, and assessing how much more likely they are as a result of greenhouse gas changes," Professor Steve Sherwood, from UNSW Sydney's Climate Change Research Centre, said in an email.

"Many have been identified, starting with the global warming of 1.1C since the mid-19th century, which is way outside the range of natural variability on that time scale but entirely consistent with expectations due to greenhouse gas increases."

Nerilie Abram, a professor of climate science at ANU's Research School of Earth Sciences, told AAP FactCheck the senator's statement is "plain wrong" and burning fossil fuels has dramatically increased the amount of CO2 in the atmosphere, "supercharging the Earth's natural greenhouse effect".

"The increased quantity of greenhouse gases in the atmosphere is causing less energy to be radiated from the Earth into space, causing Earth's surface climate to warm," she said in an email.

IN OTHER NEWS:

AAP FactCheck asked Senator Roberts' office for the source of his claim and it responded via email with an 84-page letter he sent to the prime minister and other political leaders in October 2021. It contains criticism of research the CSIRO, Bureau of Meteorology and IPCC relied on, but no evidence directly contradicting the scientific consensus on the role of carbon in global warming.

Senator Roberts has made the claim previously, including in his maiden speech to the Senate in 2016 and an ABC interview that same year. In a January 2022 episode of his podcast, he disputes fossil fuel use has any impact on carbon dioxide levels in the atmosphere and claims that nature alone controls CO2 levels, which AAP FactCheck found to be false. The senator's claims on coal-fired power stations and methane have also been fact checked here and here.

Multiple scientific organisations and studies have found the measurable increase and composition of carbon dioxide has changed the climate by warming the atmosphere, ocean and land. Climate scientists told AAP FactCheck the increase in greenhouse gases, including CO2, in the atmosphere have caused global warming.

False - The claim is inaccurate.