New Delhi, Sept. 27: Human activities appear to be the dominant cause of global warming over the past five decades, scientists said today, asserting that the evidence for human imprints on climate change is now stronger than ever before.
An international panel of scientists tasked with analysing how heat-trapping greenhouse gases are changing the planet said the human influence is visible in the warming of the air and oceans, rising sea levels, reduced snow and ice, and extreme weather events.
The Intergovernmental Panel on Climate Change (IPCC) has predicted that global surface temperature could rise by 1.5°C to 2°C by 2100 and the warming is likely to continue into the next century unless the world acts quickly to curb greenhouse gas emissions.
In its fifth assessment report released today, the IPCC also said the period from 1983-2012 was likely the warmest 30-year period over the last 1,400 years, and each of these last three decades has been successively warmer than any preceding decade since 1850.
The panel that analysed more than 7,000 scientific papers published since the last IPCC six years ago has also predicted that the sea level will continue to rise at a rate faster than has been observed over the past 40 years.
It said the warming is likely to weaken monsoon winds, but actual rainfall will increase — a scenario which implies more frequent extreme rainfall events sandwiched between relatively drier spells.
“We have more evidence now than ever before for human role in driving climate change,” said Kanikicharla Krishnakumar, a scientist with the Indian Institute of Tropical Meteorology, Pune, a member of the IPCC report’s drafting team.
The IPCC has also observed a relative slow-down in surface warming between 1998 to 2012, compared to 1951 and 1998, but scientists say this could be attributed to a slight dip in solar activity over the past decade.
“Overall, the trends are stark and clear — global warming is happening and will continue for decades to come,” Krishnakumar told The Telegraph, speaking on telephone from Stockholm where the IPCC report was released.
Scientists have suspected for decades that carbon dioxide and other greenhouse gases, primarily released through the burning of fossil fuels, trap heat from the Sun and increase global temperatures.
In its new report, the IPCC said the atmospheric concentrations of carbon dioxide, methane, and nitrous oxide have increased to levels unprecedented in at least the last 800,000 years.
The report said the oceans are absorbing much of the heat, accounting for more than 90 per cent of the energy accumulated by the planet’s climate system between 1971 and 2010. In contrast, Krishnakumar said, land has accumulated only about 5 per cent of the heat.
A senior scientist in India said the new IPCC report is unlikely to contain any “strikingly new results”, because it comes only six years after the fourth assessment conducted in 2007.
“It’s not surprising because you’re unlikely to get any dramatic new results relating to climate change in just five years,” said Jayaraman Srinivasan, chairman of the Centre for Atmospheric and Earth Sciences at the Indian Institute of Science, Bangalore.
Srinivasan said he is concerned that in the absence of dramatic short-term forecasts, countries may not take actions to curb greenhouse gas emissions fast enough to prevent some of the impacts expected during the second half of the 21st century.
“As a result of our past, present, and expected future carbon dioxide emissions, we’re committed to climate change,” Thomas Stocker, co-chair of the IPCC said in a statement. “Effects will persist for many centuries even if emissions stop.”
Environmental groups responded to the IPCC report with calls on governments to act fast.
“It’s not too late to change course, but we need actions to reduce global emissions and expedite the shift to clean energy,” said Andrew Steer, President of the non-government World Resources Institute (WRI) in Washington DC.
The WRI official has cautioned that extreme weather events, heat waves, rising sea levels, and erratic rainfall could disrupt food supplies, displace populations, undermine prospects for future economic growth, and hurt poor communities the most.