If you ask people where the hottest place on Earth is, most will reply “Death Valley". However, that’s not necessarily true.
Furnace Creek in California’s Death Valley holds the official record for the highest air temperature on the planet, clocking a scorching 56.7°C (134.1°F) on July 10, 1913. While some dispute the validity of the temperature recording (and even if they do, the next record-breaker is still Furnace Creek just nine days earlier), that’s the official hottest temperature according to the World Meteorological Organization (WMO).
However, if we look at land surface temperature then two other locations are miles ahead of Death Valley. In a new study published in Bulletin of the American Meteorological Society, scientists in the US used satellite data to show that the Lut Desert in Iran and the Sonoran Desert in Mexico have seen baking land surface temperatures of 80.8°C (177.4°F) in recent decades.
A surface temperature of -110.9°C (-167.62°F) in Antarctica was recorded as the lowest temperature recorded in the study, approximately 20°C lower than what was reported by the WMO, which has the lowest temperature as -89.2°C (-128.56 °F). The biggest swing of temperature was found in the Qaidam Basin in China where the land surface temperature was found to have fluctuated by 81.8°C (147.3°F) in a single day, from -23.7°C (-10.7°F) to 58.1°C (136.6°F).
Air temperatures are recorded using over 10,000 weather stations across the world maintained by the WMO. Typically, the temperature is gauged using a Stevenson screen, a ventilated white-painted box that’s lifted a few feet off the ground. This design allows air to flow through but avoids direct sunlight that may skew the results.
In this new study, the researchers used an alternative method. Instead of measuring air temperature, they measure how hot the actual ground surface was using data from NASA's Moderate Resolution Imaging Spectroradiometer (MODIS) onboard its Earth-observation satellites. Along with measuring land surface temperature, MODIS gathers data on the oceans and the lower atmosphere.
Measuring air temperature and land surface temperature can give very different results, as this study suggests. Imagine you are on a beach on a summer's day: the sand beneath your feet is going to feel noticeably hotter than the air around your chest. This is because the land surface absorbs more solar radiation and retains more heat. Land surface temperature can also be dictated by the shape and material of the landscape; a big black rock will absorb more heat than white sand, for instance.
When scientists talk about climate change, rising temperatures generally refer to the near-surface air temperature, but researchers know relatively little about how climate change might be affecting land surface temperatures. The study authors of this new research suspect that the extreme temperatures documented in Iran’s Lut Desert and Mexico’s Sonoran Desert could be a reflection of human-driven climate change, but there is currently not enough data to separate it from natural variability.
"While the behavior of the atmosphere in response to more anthropogenic emissions is well studied, the response of the land surface under different emission pathways is not well understood," the researchers conclude. "It is hoped the future research in this direction can shed light on not only how extremes have changed in the past but how they will likely affect our planet in the future."