A graph purporting to show the fluctuation of global temperatures over the last four decades has been shared thousands of times in social media posts that misleadingly claim it proves “CO2-driven warming is a hoax” and undermines the theory that all CO2 emissions warm the planet. But experts told AFP the graph shows a warming trend and that social media users had “cherry-picked” its data. Climatologists have measured how emissions from human activities have caused global warming.
“NASA satellite data make it official: January 2023 was colder than January 1987… despite a doubling of manmade CO2 in the atmosphere,” reads a claim shared here on Twitter by Fox News commentator Steve Milloy on February 3.
“The global warming con is every CO2 emission warms the planet. That is obviously not true. CO2 warming is a hoax,” he continued.
The claim was shared alongside a graph dataset titled: “UAH Satellite-Based Temperature of the global lower atmosphere (version 6.0)”.
The dataset – published by a University of Alabama in Huntsville scientist Roy Spencer – shows global average tropospheric 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 graph spans a more than four-decade period from 1979 until early 2023.
Despite fluctuations, it appears to show a gradual increase in the Earth’s satellite-based readings for the temperature of the global troposphere — the first and lowest layer of Earth’s atmosphere. The troposphere extends from the Earth’s surface to about 12 kilometres (7.5 miles) in height, according to NASA.
NASA considers satellite measurements to be less precise than thermometers on the ground for measuring global temperatures.
The warming trend over recent decades is mirrored in data sets used by international sources including the European Centre for Medium-Range Weather Forecasts (ECMWF – the ERA5 dataset used by Copernicus) and the NOAA’s GlobalTemp set.
The Intergovernmental Panel on Climate Change (IPCC)’s 2021 report stated that “it is unequivocal that human influence has warmed the atmosphere, ocean and land”.
Fossil fuels — coal, oil, and gas — are the main contributor to global climate change, responsible for over 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 human-caused 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.
Andrew King, a senior lecturer in climate science at The University of Melbourne, said Milloy “cherry-picked” the data and the graph “clearly shows” a warming trend.
He cited global surface temperature, rising sea levels and reductions in sea ice extent as factors to show “human-caused global warming”.
“Global surface temperature shows (the Earth) is around 1.2 degrees Celsius (2.16 degrees Fahrenheit) warmer since the late 19th century,” King told AFP on February 8.
The average global temperature in 2022 was about 1.15C (2.07F) above 1850-1900 levels, making the last eight years the warmest on record, according to the World Meteorological Organization.
Global average sea level has risen 21–24 centimetres (eight to nine inches) since 1880, while summer Arctic sea ice extent is shrinking by 12.6 percent per decade as a result of global warming.
The IPCC forecast that average global temperatures could reach or exceed 1.5C (2.7F) of warming over the next 20 years due to emissions of greenhouse gases from human activities.
La Nina cooling effect
Neville Nicholls, a professor of earth atmosphere and environment at Monash University, said the global warming trend has been offset over the last two years by the sequence of La Nina episodes.
La Nina is a climate pattern in the Pacific Ocean that can affect weather worldwide. During a La Nina year, cooler-than-average sea-surface temperatures occur in the tropical Pacific.
“We have known for many years that La Nina episodes cause global temperatures to be a bit cooler than might otherwise be expected,” Nicholls told AFP on February 8.
Climate scientist Nick Dunstone said in the 2023 global temperature forecast published by the Meteorological Office of the UK that the global temperature over the last three years has been influenced 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 lead to global temperature in 2023 being warmer than 2022,” Dunstone noted.
AFP has previously debunked a misleading claim using the UAH data here and climate misinformation shared by Milloy here and here.