A global warming pause may be natural, as per researchers, who say any reduction in warming should not be interpreted as a sign anthropogenic warming has lessened.
Shaun Lovejoy of McGill University in Canada performed statistical analysis of global temperatures during the period from 1998 to 2013. The physics professor found a slowing of global warming during these years can be attributed to natural fluctuations.
Temperatures have continued to rise since 1998, although the rate at which they are climbing have been moderated during that period of time. Carbon dioxide levels have continued to rise, even as global warming has slowed over the last 15 years. This pause has led some critics of the idea of anthropogenic warming to claim human activities are not significantly contributing to rising global temperatures.
A natural decline of temperature of between 0.5 and 0.67 degrees Fahrenheit has taken place each of the last 15 years, says Lovejoy. Similar cooling patterns occur around once every 20 to 50 years, based on new research.
The method of analysis used in the study was originally developed by Lovejoy, and detailed in the April 2014 of Climate Dynamics. In the earlier investigation, the researcher and his team studies pre-industrial conditions, in order to analyze historical records. From that study, the McGill Physicist was able to conclude - with 99 percent certainty - that global warming in the industrial age is caused by human activities.
Natural cooling periods, like those that could account for a reduction in the rise of global temperatures over the last 15 years, were often seen in historical data collected for the earlier study.
"We find many examples of these variations in pre-industrial temperature reconstructions [using tree rings, ice cores etc.]. Being based on climate records, this approach avoids any biases that might affect the sophisticated computer models that are commonly used for understanding global warming," Lovejoy said.
The scientist also noted a warming period, which lasted from 1992 to 1998, as part of the natural trend that has occurred throughout history.
"The pause thus has a convincing statistical explanation," Lovejoy stated in a press release from McGill University.
This investigation may assist other climate researchers in analyzing trends in precipitation, and well as local variations in climate in different parts of the world. Modeling of future conditions could also benefit from the use of probability theory in the investigation.
Study of global climate fluctuations and their possible contribution to the moderation of rising global temperatures since 1998 was published in the journal Geophysical Research Letters.
