The causes are impacts of global warming and climate change are quite controversial, with some suggesting that the increased temperatures predicted by climate studies in recent years are exaggerated. Now, a new NASA-led study seeks to put these suggestions to rest, reporting that nearly one-fifth of the global warming that has occurring in the past 150 years has been missed by historical records due to quirks in global temperature recording methods.

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Although we know that the Arctic is warming faster than the rest of the Earth, its inaccessible location means that few historic records possess temperature readings from this region in comparison to lower latitudes. Due to this difficulty in data collection, many reports show less warming than climate models due to their inability to fully represent the Arctic.

In addition, historical models mix air and water temperatures, as opposed to climate models, which refer to air temperatures only. Ultimately, this skews historical temperature measurements toward the cool side since water warms less than air.

The team behind the current study attempted to resolve these discrepancies by pinpointing the quirks in historical temperature records and applying them to climate model output. They conducted the same calculations on both the models and observations and compared the warming rates, revealing that with the modification in place, the models and observations are very similar in their expected near-term global warming data.

The study marks the first time that the impact of these quirks have been calculated.

“They’re quite small on their own, but they add up in the same direction,” said Mark Richardson of NASA’s Jet Propulsion Laboratory, Pasadena, California and lead author of the study. “We were surprised that they added up to such a big effect.”

The quirks examined in the study are estimated to have hid approximately 10 percent of global air-temperature since the 1860s, which is enough to push historical record temperature calculations significantly lower than the majority of the results from climate models used by the Intergovernmental Panel on Climate Change (IPCC) for its assessment reports.

“Researchers should be clear about how they use temperature records, to make sure that comparisons are fair,” Richardson said. “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.”

Journal Reference: Reconciled climate response estimates from climate models and the energy budget of Earth. 27 June 2016. 10.1038/nclimate3066