There’s been a huge debate in the last couple of years over the so-called pause in global warming and what it means for the future of the planet.
On one side, skeptics argue that there has been no warming for the last 18 years or so. On the other side, environmentalists and some scientists argue that the globe is still warming. In fact, they argue that the last three decades have been warmer than any preceding decade going back over a century.
While both sides are well intentioned, it’s this humble journalist’s opinion that the crossfire is only serving to confuse the public (and the media for that matter) on one of the most hot button issues of our time.
Whether or not you think global warming is a problem, lawmakers and bureaucrats are passing laws and writing rules based on claims that fossil fuel use is warming the planet. So it’s important to understand how both sides of the climate debate can have two completely separate sets of conclusions on the state of global warming.
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How can agencies like the National Oceanic and Atmospheric Administration report things like the “combined average temperature over global land and ocean surfaces for September 2014 was the highest on record for September” while skeptical observers report that September’s average global temperatures were only the seventh (and ninth) highest ever recorded?
The answer has to do with what data one looks at. NOAA, for example, uses surface temperature measurements while skeptics often rely on satellite data.
“The NOAA temperature dataset represents the surface temperature, rather than the lowest few miles of the atmosphere, and is derived from direct measurements at weather stations on land, and by ships and buoys at sea,” Deke Arndt, chief of the Climate Monitoring Branch at NOAA’s National Climatic Data Center, told The Daily Caller News Foundation.
NOAA presents global land and sea “temperature anomalies” based on readings taken from thousands of weather stations, ocean buoys and ships around the word. The problem is that weather stations and such can’t cover the entire world, so NOAA has to improvise.
“Absolute estimates of global average surface temperature are difficult to compile for several reasons,” according to NOAA’s website. “Some regions have few temperature measurement stations (e.g., the Sahara Desert) and interpolation must be made over large, data-sparse regions.”
To correct for this, NOAA calculates a baseline temperature for the region using “reference values computed on smaller [more local] scales over the same time period” to normalize data and “more accurately represent temperature patterns with respect to what is normal for different places within a region.”
NOAA says, “Anomalies more accurately describe climate variability over larger areas than absolute temperatures do, and they give a frame of reference that allows more meaningful comparisons between locations and more accurate calculations of temperature trends.”
But this is exactly the criticism skeptics have of NOAA’s method of temperature readings, which is why they argue that satellite data is better at calculating global temperature averages than surface readings.
“I claim 2014 won’t be the warmest global-average year on record,” writes Dr. Roy Spencer, climate scientist at the University of Alabama, Huntsville, “if for no other reason than this: thermometers cannot measure global averages — only satellites can.”
“The satellite instruments measure nearly every cubic kilometer – hell, every cubic inch — of the lower atmosphere on a daily basis. You can travel hundreds if not thousands of kilometers without finding a thermometer nearby,” Spencer writes.
Satellite datasets “represent the lowest few miles of the atmosphere,” Arndt told TheDCNF, and “are derived from the microwave sounding units… of various different satellites over time whose records have been spliced together to make a continuous record.”
The two main satellite temperature data sets are the University of Alabama, Huntsville dataset (where Spencer works) and the Remote Sensing Systems dataset. These satellite datasets show that there has been no global warming trend for more than 18 years — over half the satellite temperature record.
Skeptics also argue surface temperature measurements are problematic because “thermometers are placed where people live, and people build stuff, often replacing cooling vegetation with manmade structures that cause an artificial warming,” Spencer writes.
NOAA has made advances in weeding out this so-called urban heat island (UHI) effect from cities, but Spencer argues that NOAA’s “data adjustment processes in place cannot reliably remove the UHI effect because it can’t be distinguished from real global warming.”
“Satellite microwave radiometers, however, are equipped with laboratory-calibrated platinum resistance thermometers, which have demonstrated stability to thousandths of a degree over many years, and which are used to continuously calibrate the satellite instruments once every 8 seconds,” Spencer argues. “The satellite measurements still have residual calibration effects that must be adjusted for, but these are usually on the order of hundredths of a degree, rather than tenths or whole degrees in the case of ground-based thermometers.”
But critics say satellite records don’t prove the world has stopped warming. Satellites don’t measure actual temperatures, they measure variances in wavelength bands which are then converted into temperatures, so different conversion methods yield different results. For example, UAH and RSS both show a “pause” in global warming, but UAH data shows slightly more warming than RSS data does.
Critics of satellite data also say that the data collected is not homogeneous as it’s collected from a series of satellites that don’t have completely identical instrumentation and that satellite sensors degrade over time along with their orbit.
“Reconciling and understanding the differences between these different ways of measuring different parts of the climate system has been an active area of research and related work for more than a decade,” said Arndt.
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