Leading scientists around the world are now 95 percent confident that human influence is the dominant cause of global warming, according to the Fifth Assessment Report by the Intergovernmental Panel on Climate Change (IPCC), released Friday.
Statistically speaking, this means that that the debate is over — climate change is occurring due to human action. As a result of past, present and expected future emissions of carbon dioxide, the effects of climate change will persist for many centuries even if carbon dioxideemissions stop, IPPC says.
The organization says the evidence for this has grown, thanks to more and better observations, an improved understanding of the climate system response and improved climate models.
Since the 1950s, there has been an unmistakable warming in the climate system and many observed changes are unprecedented over decades and even millennia. Each of the last three decades has been successively warmer at the Earth’s surface than any preceding decade since 1850, the report cites.
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Observations of changes in the climate system were based on multiple lines of independent evidence. IPCC assessed that the atmosphere and ocean have warmed, the amount of snow and ice has diminished, the global mean sea level has risen and the concentrations of greenhouse gases have increased.
"Continued emissions of greenhouse gases will cause further warming and changes in all components of the climate system,” said Thomas Stocker, Co-Chair of IPCC’s Working Group I. “Limiting climate change will require substantial and sustained reductions of greenhouse gas emissions."
IPCC says global surface temperature change for the end of the 21st century is projected to be likely to exceed 1.5°C relative to 1850 to 1900 in all but the lowest scenario considered, and likely to exceed 2°C for the two high scenarios.
Stocker warned this could lead to increasingly catastrophic climate conditions.
“Heat waves are very likely to occur more frequently and last longer. As the Earth warms, we expect to see currently wet regions receiving more rainfall, and dry regions receiving less, although there will be exceptions,” he added.
Projections of climate change are based on a new set of four scenarios of future greenhouse gas concentrations and aerosols, spanning a wide range of possible futures. The report assessed global and regional-scale climate change for the early, mid- and later 21st century.
As the ocean warms, and glaciers and ice sheets reduce, global mean sea level will continue to rise, but at a faster rate than the planet has experienced over the past 40 years, the report claims. Ocean warming dominates the increase in energy stored in the climate system, accounting for more than 90 percent of the energy accumulated between 1971 and 2010.
The private sector has become more vocal in urging policymakers to take strong action against climate change. Last month, a half-dozen more leading global companies including Microsoft, Owens Corning, Diageo, Thornton Tomasetti and Acer America Corporation joined hundreds of other U.S. businesses in signing the Climate Declaration, which calls on federal policymakers to seize the economic opportunity of addressing climate change.