By Jonny Lupsha, Wondrium Staff Writer
Climate averages updated once per decade will rise, affecting weather forecasting. The current range of dates used for estimates is from 1981 to 2010, but the baseline from 1991 to 2020 will bump averages up. How do we take Earth’s temperature?
On May 4, the National Oceanic and Atmospheric Association (NOAA) will officially bring the 30-year “climate normals” up by a decade. These are average temperatures for the United States that meteorologists use to forecast the weather and set expectations. For the last decade, the span of time used to calculate climate normals was 1981 to 2010, but with the data from 2020 now complete, NOAA will soon use 1991 to 2020 as their range—and climate averages are creeping up.
With varying altitudes and environments spread across the globe, how do we take Earth’s temperature? In his video series Earth’s Changing Climate, Dr. Richard Wolfson, the Benjamin F. Wissler Professor of Physics at Middlebury College, explained.
The Best System We’ve Got
“Only at about the mid-19th century, about the year 1850, did we have enough data from all around the world to calculate a statistically meaningful average temperature,” Dr. Wolfson said. “How did we do that? First of all, there are air temperatures, and they’re coming from basically land-based weather stations, which place their thermometers in particular standard locations [at eye level], about a meter and a half.
“They measure what’s called surface air temperature, or SAT.”
Additionally, Dr. Wolfson said, marine air temperatures (MATs) are taken by buoys and ships. When the SATs and MATs have been measured all around the world, they’re combined with careful statistical analyses in order to compute an average temperature for the whole world. It also requires very subtle scientific work, including making corrections.
“Weather stations may move, [or] they may replace their instrumentation, and that has to be corrected for,” Dr. Wolfson said. “Water temperature sampling requires particular corrections. Modern ships take the temperature at the intake water to their engines, so that doesn’t require as much correction.”
In the old days, he said, they’d throw a bucket overboard, fill it with water, haul it up and take the temperature. Depending on the materials comprising the bucket of water, temperature was affected.
City Life and the Weather Station
Another factor that can affect taking the global average temperature centers around urban development.
“One of the most significant changes that you may have heard about is what’s called the urban heat island effect,” Dr. Wolfson said. “If you imagine a weather station that, for example, was 100 years ago on the outskirts of a city, cities tend to be warmer than their surroundings because they’ve changed the land’s reflectivity by paving roads.
“They generate a lot of energy themselves, which causes local heating.”
If a weather station was built 100 years ago on the outskirts of a city, chances are it’s surrounded by a city now, meaning the weather station is warmer and would report false data that reflects global warming. Is urban development responsible for the numbers that cause the climate change scare?
“Fortunately, we can test for that effect,” Dr. Wolfson said. “In these huge data sets, which have thousands of places reporting, we can simply take out the places that represent large urban areas, and we find that the global temperature record doesn’t change much; maybe a few hundredths of a degree. There’s a slight effect there—if we want to get very accurate, we correct for it—but the urban heat island effect is not the reason why we have the global temperature rise.”
Regardless of its causes, “above normal” is about to be the new normal.