A graph that purports to show the fluctuation of global temperatures over the past four decades has been shared thousands of times in social media posts misleadingly claiming it proves “CO2-driven warming is a hoax” and undermines the theory that all CO2 emissions are warming the planet. But experts told AFP the chart shows a warming trend and that social media users had “picked” the data. Climatologists have measured how emissions from human activities have caused global warming.
“NASA satellite data makes it official: January 2023 was colder than January 1987…despite a doubling of human-made CO2 in the atmosphere,” reads a claim shared here on Twitter by Fox News commentator Steve Milloy at 3 February.
“The downside of global warming is that any CO2 emissions warm the planet. That is clearly not true. Global warming is a hoax,” he continued.
A screenshot of the misleading claim, captured on February 10 (Kate TAN)
The claim was shared alongside a graphical dataset titled: “UAH Satellite-Based Temperature of the global lower atmosphere (version 6.0)”.
The dataset – published by Roy Spencer, a scientist from the University of Alabama at Huntsville – shows average troposphere temperatures measured in degrees Celsius based on satellite data from the National Aeronautics and Space Administration (NASA) and the National Oceanic and Atmospheric Administration (NOAA) .
The chart spans a period of more than four decades from 1979 to early 2023.
Despite fluctuations, it appears to show a gradual increase in Earth’s satellite-based measurements for the temperature of the global troposphere — the first and lowest layer of Earth’s atmosphere. The troposphere extends from Earth’s surface to about 12 kilometers (7.5 miles) high, according to NASA.
NASA considers satellite readings less accurate than ground-based thermometers for measuring global temperature.
The warming trend of recent decades is reflected in datasets used by international sources, including the European Center for Medium-Range Weather Forecasts (ECMWF – the ERA5 dataset used by Copernicus) and NOAA’s GlobalTemp set.
The 2021 Intergovernmental Panel on Climate Change (IPCC) report stated that “it is unequivocal that human influence has warmed the atmosphere, ocean and land”.
Fossil fuels – coal, oil and gas – are the largest contributors to global climate change, responsible for more than 75 percent of global greenhouse gas emissions and nearly 90 percent of all carbon dioxide emissions. The emissions cause global warming and climate change by trapping the sun’s heat around the earth.
AFP has debunked claims that global warming is natural and not caused by man-made carbon emissions.
The same dataset alongside a similar claim has been shared among social media users in Germany, the UK and Australia.
But the claim is misleading.
Warming trend
Andrew King, a senior lecturer in climate science at the University of Melbourne, said Milloy “sorted out” the data and the graph “clearly shows a warming trend”.
He cited global surface temperature, rising sea levels and reduction in sea ice as factors to demonstrate “man-made global warming”.
“Global surface temperature shows that (the Earth) is about 1.2 degrees Celsius (2.16 degrees Fahrenheit) warmer since the late 1800s,” King told AFP on Feb. 8.
The average global temperature in 2022 was about 1.15°C (2.07°F) above 1850-1900 levels, making the past eight years the warmest on record, according to the World Meteorological Organization.
The global mean sea level has risen by 21-24 centimeters since 1880, while summer sea ice is shrinking at a rate of 12.6 percent per decade due to global warming.
The IPCC predicts that global average temperatures could reach or exceed 1.5°C (2.7°F) over the next 20 years due to greenhouse gas emissions from human activities.
La Nina cooling effect
Neville Nicholls, a professor of Earth’s atmosphere and environment at Monash University, said the trend of global warming over the past two years has been offset by the succession of La Nina episodes.
La Nina is a Pacific Ocean climate pattern that can affect weather worldwide. Cooler-than-average sea surface temperatures occur in the tropical Pacific during a La Nina year.
“We’ve known for many years that La Nina episodes cause global temperatures to be somewhat cooler than would otherwise be expected,” Nicholls told AFP on Feb. 8.
Climate scientist Nick Dunstone said in the 2023 global temperature forecast published by the Meteorological Office of the UK that global temperatures over the past three years have been affected by the effect of a prolonged La Nina.
He added that the climate pattern is expected to end in 2023 with a return to relatively warmer conditions in parts of the tropical Pacific.
“This shift is likely to result in global temperatures being warmer in 2023 than in 2022,” Dunstone noted.
AFP has previously debunked a misleading claim using the UAH data here and climate misinformation shared by Milloy here and here.