Earth's temperature depends on where you put thermometer

January 20, 2016 bySeth Borenstein

When it comes to measuring global warming, it's all about altitude.

Temperature readings taken close to Earth's surface—about 6 feet off the ground—show a slightly warmer planet than measurements taken from on high by satellites in orbit.

And that discrepancy has given ammunition to climate-change doubters.

Government agencies and most scientists rely primarily on , and they show that 2015 was the warmest year on record.

The National Oceanic Atmospheric Administration, NASA, the Japanese and British meteorological agencies and the World Meteorological Organization all use ground data. It's a matter of better accuracy and relevance, scientists say.

"We care about what's happening where we live. That's why ground-based temperatures are most relevant to humans," said Texas Tech climate scientist Katharine Hayhoe.

But those who try to cast doubt on accepted science—most often non-scientists—prefer that goes back to 1979. And the data shows that 2015 was only the third-warmest year on record.

Politicians who reject mainstream climate science, such as Republican presidential candidate Ted Cruz, especially cite one satellite measurement system, Remote Sensing Systems, in asserting that there has been no for 18 years. That's a claim scientists, including the one who runs RSS, say is misleading.

Carl Mears, senior scientist for Remote Sensing Systems, told The Associated Press in an email: "The do not measure the surface . They are measurements of the average temperature of thick layers of the atmosphere" about 50,000 feet off the ground.

"For impacts on human society and the environment, the surface data are more important," Mears said.

Mears said his analysis of his own satellite data has five times the margin of error of ground measurements. That's because satellites use complex mathematical algorithms and thousands of bits of code to translate wavelength measurements into , Hayhoe said.

Scientists routinely use ground measurements to calibrate and validate satellite information, said Marshall Shepherd, a University of Georgia meteorology professor. He and several other scientists called surface measurements "the ground truth."

John Christy at the University of Alabama, Huntsville, who runs a separate satellite temperature monitoring system, said satellites are better for detecting warming from heat-trapping gases because the "surface is affected by too many other variables and doesn't represent the real mass of the climate system."

Both Christy's and Mears' satellite data show that the world has warmed since about 1980, when satellites started measuring temperature. The two systems show about seven-tenths of a degree of warming in the past 35 years, while ground data shows about a full degree.

Explore further: NOAA, NASA: 2015 was Earth's hottest by a wide margin

Related Stories

Satellites find sustainable energy in cities

December 21, 2015

Underground heat islands in cities have an enormous geothermal potential. Warm groundwater can be used to produce sustainable energy for heating and cooling. Researchers of Karlsruhe Institute of Technology (KIT) have now ...

Is global warming hiding underwater?

February 10, 2014

Satellite observations of global sea-surface temperature show that a 30-year upward trend has slowed down within the last 15 years. Climate scientists say this is not the end of global warming, but the result of a rearrangement ...

Understanding the impact of snow's reflectance

December 10, 2015

To help improve the accuracy of climate models, an international team involving the National Physical Laboratory (NPL) has measured the reflectance of rough, snow-covered surfaces at large solar zenith angles.

Recommended for you

Mystery solved for mega-avalanches in Tibet

January 23, 2018

An international scientific effort determined the cause of a highly unusual and deadly glacier avalanche in Tibet in 2016, a new Nature Geoscience paper says.

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

not rated yet Jan 21, 2016
Whether temperatures taken on the ground, in the air or via satellite, the end result is the same; global warming is real irregardless to whether or not 2015 where is the hottest year on record.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.