Though the last three decades have been the warmest, there appears to be a hiatus in change of average temperature in the last 20 years even as global warming continues unchecked.
The recently released fifth Inter-governmental Panel on Climate Change (IPCC) report explains this pause in variation of temperature that may not be reflective of a trend.
“A part of the heat is absorbed by the deep ocean waters at 700 meters depth while the upper levels of the ocean remain cooler,” the report states.
Govindswamy Bala, Associate Professor, Divecha Centre for Climate Change at the Indian Institute of Science (IISc), said at a discussion on the report at IISc that temperature changes are apparent only if examined over longer time periods, say 30 years.
“If one looks at the last 30 years, a steady increase in global temperature is evident. Data of just 10 years may show a hiatus or even cooling periods,” Prof Bala said.
The IPCC report merely summarises five years of research and the fifth report has 14 chapters written by 259 authors from 30 countries. Prof Bala has also written a few chapters in the report.
Prof J Srinivasan, Chairperson of the Centre, told Express, “The hiatus is not completely unexplained. It was just that there were many unexplained factors. Now we have succeeded in explaining the process, partially, just as we have explained the predicted rise of about one metre in sea levels. We need better climate models in order to explain and predict future climate change.”
‘3,000 Decatons Ice Lost in 20 Years’
The report also predicts a steep rise in temperatures and rapid decline in sea ice levels.
It says that 3,000 decatons of ice were lost in the last 20 years. It also notes the contribution of glaciers and ice sheets to the rise in sea levels.
Further, the report throws light on the important roles of soot, methane and black carbon in global warming.
“The report indicates that as carbon dioxide levels rise, oceans will get more acidic. This will have a huge impact on marine life,” Bala said.
“The IPPC report discusses geo-engineering methods such as limiting the amount of sunlight that enters the earth by spraying particles in the air that will reflect it back and removing carbon dioxide by artificial means. Carbon and warming have a linear relation. Future emissions must not exceed 450 PgC to avoid 2 Kelvin global warming,” he warned.
Anil G Kulkarni of the Centre also forewarned, “The report says Himalayan glaciers are retreating at 0.5 per cent per year.”