Graph uses ‘selective’ data in misleading posts about CO2-driven global warming: experts

A graph purporting to show global volatility temperatures over the past four decades shared thousands of times in social media posts that misleadingly claim to prove “CO2-driven warming is a hoax” and undermine the theory that all CO2 emissions are warming the planet. But experts told AFP that the graph shows a warming trend and that its data had been “picked” by social media users. Climatologists have measured how emissions from human activities have contributed to global warming.

“NASA satellite data makes it official: January 2023 was colder than January 1987… despite a doubling of man-made CO2 in the atmosphere,” reads a claim shared here on Twitter by Fox News commentator Steve Milloy on February 3.

“Global warming is that every CO2 emission warms the planet. That is clearly not true. CO2 warming is a hoax,” he continued.

Screenshot of the misleading claim, captured on February 10 (Kate TAN)

The claim was shared alongside a graph dataset titled: “Satellite-Based Temperature of the global lower atmosphere (version 6.0)”.

The dataset – published by University of Alabama in Huntsville scientist Roy Spencer – shows global average tropic 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 covers a period of more than four decades from 1979 to the beginning of 2023.

Despite fluctuations, Earth satellite readings for the temperature of the global troposphere – the first and lowest layer of the Earth’s atmosphere – appear to show a gradual increase. The troposphere extends from the Earth’s surface to about 12 kilometers (7.5 miles) high, according to NASA.

NASA considers satellite measurements to be less accurate than ground-based thermometers for measuring global temperature.

The warming trend in recent years is evident in datasets used by international sources including the European Center for Medium-Range Weather Forecasts (ECMWF – ERA5 dataset used by Copernicus) and NOAA’s GlobalTemp dataset.

The 2021 report of the Intergovernmental Panel on Climate Change (IPCC) stated that “it is clear that human influence has warmed the atmosphere, oceans and land”.

Fossil fuels – coal, oil and gas – are the biggest contributors to global climate change, responsible for more than 75 per cent of global greenhouse gas emissions and almost 90 per cent of carbon dioxide emissions all. The emissions cause global warming and climate change by trapping the Sun’s heat around the Earth.

AFP has dismissed claims that global warming is natural and not caused by human carbon emissions.

The same dataset was shared with similar demand among social media users in Germany, the UK and Australia.

But the claim is misleading.

A warming trend

Andrew King, a senior lecturer in climate science at the University of Melbourne, said Milloy had “selected” the data and the graph “clearly shows a warming trend”.

He cited global surface temperatures, rising sea levels and reductions in sea ice extent as factors that indicated “human-caused global warming”.

“The global (Earth) surface temperature shows about 1.2 degrees Celsius (2.16 degrees Fahrenheit) warmer since the end of the 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 it the eight warmest years on record, according to the World Meteorological Organisation.

Average global sea level has risen 21–24 centimeters (eight to nine inches) since 1880, and the extent of summer Arctic sea ice is decreasing by 12.6 percent per decade as a result of global warming.

The IPCC has predicted that global average temperatures could reach or exceed 1.5C (2.7F) of warming over the next 20 years due to greenhouse gas emissions from human activities.

The cooling effect of La Nina

Neville Nicholls, professor of atmosphere and global environment at Monash University, said the global warming trend has been offset over the past two years by a succession of La Nina episodes.

La Nina is a climate pattern in the Pacific Ocean that can affect weather around the world. During a La Nina year, cooler than average sea surface temperatures occur in the tropical Pacific Ocean.

“We’ve known for many years that La Nina episodes cause global temperatures to be slightly cooler than would otherwise be expected,” Nicholls told AFP on February 8.

Climate scientist Nick Dunstone said in the 2023 global temperature forecast published by the United Kingdom’s Met Office that the global temperature over the past three years has been influenced by the long La Nina effect.

He added that the climate pattern is expected to end in 2023 and return to relatively warmer conditions in parts of the tropical Pacific.

“The global temperature in 2023 is likely to be warmer than 2022 as a result of this change,” Dunstone noted.

AFP has previously debunked a misleading claim using UAH data here and the climate misinformation shared by Milloy here and here.

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