A research team including a Scripps Institution of Oceanography at the University of California San Diego climate scientist simulated in a computer model, for the first time, the realistic evolution of global mean surface temperature since 1900. In doing so, the researchers also created a new method by which researchers can measure and monitor the pace of anthropogenic global warming, finding that the contribution of human activities to warming in the surface waters of the Pacific Ocean can be distinguished from natural variability.

Former Scripps researcher Yu Kosaka, now at the University of Tokyo, and Shang-Ping Xie, the Roger Revelle Chair in Environmental Science at Scripps, created the simulation by forcing sea surface temperature over the tropical Pacific to follow the observed variability.

"The climate system includes naturally occurring cycles that complicate the measurement of global warming due to the anthropogenic increase in atmospheric greenhouse gases," said Xie. "We can isolate the anthropogenic warming by removing the internally generated natural variability."

Climate policymakers have sought to limit the rise of global temperatures to 2° Celsius higher than pre-industrial levels. That figure is considered a threshold beyond which society and natural systems are virtually assured of experiencing significant and dangerous instability. Scientists have estimated that the planet is already roughly 1° C warmer at the surface than before the Industrial Revolution.

The 2° C target was reaffirmed during the 2015 Conference of the Parties, known as COP21, that was held in Paris in December. Kosaka and Xie's research could provide an easily generated and more accurate means to measure society's success in keeping temperatures below that threshold.

The research is further confirmation of the primary importance of the Pacific in controlling global-scale climate that researchers have come to understand in recent decades. Kosaka and Xie plotted the rise of global mean temperatures over the past 120 years. The rise of temperatures ascends in a staircase fashion with the steps becoming larger over the past 50 years.