Global warming, the increase of Earth's average surface temperature, caused by human activities has halted 1,800 years of steady cooling trend in the oceans of the world, revealed a new research. Second author of the study Michael Evans, associate professor at University of Maryland in the US, said, "Today, the Earth is warming about 20 times faster than it cooled during the past 1,800 years. This study truly highlights the profound effects we are having on our climate today."
The study found that the coolest temperatures occurred during the Little Ice Age, a period that spanned the 16th through 18th centuries and was known for cooler average temperatures over land. The concurrence of cooling events on both land and sea suggests that a global cooling phenomenon was erased by subsequent global warming.
Lead author Helen McGregor from University of Wollongong in New South Wales, Australia, said, "With this research, we now have new insight into the century-scale global sea-surface temperature variations that came before man-made greenhouse gas forcing."
The researchers combined 57 previously published marine surface temperature reconstructions that cover all of the world's oceans, from near-polar to tropical regions. They compiled the data within 200-year brackets to observe long-term trends, and then compared the findings to land-based reconstructions, which revealed similar cooling trends. To investigate the cause of the cooling trend, the research team turned to climate models. They examined how sea-surface temperatures reacted to various 'forcing' factors, such as changes in solar output, Earth's orbit, land use, volcanic activity and greenhouse gases.
The study was published in Nature Geoscience.