Estimates based on historical temperature records gives wrong result.
By: AB Wire
A study conducted by a group of scientists from NASA has found that nearly 20 percent of the global warming that has happened in past 150 years has been underestimated due to the quirks in the method of recording the global temperature.
The study conducted by a team headed by Mark Richardson of NASA’s Jet Propulsion Laboratory, Pasadena, California, suggests that global warming projections based on historical data may go wrong because of the quirks in the recorded data.
The scientists applied the quirks in the historical records to climate model output and then performed the same calculations on both the models and the observations to make the first true apples-to-apples comparison of warming rates. They found that both the results were almost equal to the expected global warming for upcoming years.
A clear example of the peculiarity of temperature recording is that of the Arctic which is warming at a higher rate than the rest of the world. But, due to the inaccessible nature of the Arctic, fewer historic temperature rates from the region were recorded in the past compared to lower altitude areas. As a result of this, the combined data shows a lower rate of global warming compared to a climate model that fully represents the Arctic.
The study also noted two more issues associated with historical data recording. While the climate model considers only the air temperature, the historical recording mixes both air and water temperature. So, the measurement based on historical data skew towards cool side as the water temperature is less warm than the air.
The second problem is that when temperature recordings began in the 1860s, only air temperatures from the Arctic and adjacent areas were taken into consideration. There were more sea-ice-covered areas in the Arctic during the period. But, when the ice melted in subsequent years, the researchers switched to water temperature. This also resulted in bringing down the global warming indicators from the actual figures.
Mark Richardson said that the scientists have known about the quirks for some time. “They’re quite small on their own, but they add up in the same direction. We were surprised that they added up to such a big effect,” he said.
These quirks in the historical recording have hidden almost 19 percent of the global warming since the 1860s. This is the reason for the estimates made from the historical records showing cooler temperature than the results from the climate models that the Intergovernmental Panel on Climate Change (IPCC) uses.
“Researchers should be clear about how they use temperature records, to make sure that comparisons are fair. It had seemed like real-world data hinted that future global warming would be a bit less than models said. This mostly disappears in a fair comparison,” said Richardson.
The study is published in the journal Nature Climate Change.