If the public and policymakers want a single adjective to describe the findings of the Intergovernmental Panel on Climate Change's new assessment report that's the word.
Released Friday, the IPCC report states, that "warming in the climate system is unequivocal and since 1950 many changes have been observed throughout the climate system that are unprecedented over decades to millennia."
"Our assessment of the science finds 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,” said Qin Dahe, Co-Chair of IPCC Working Group I, responsible for this first stage of the IPCC's reporting on climate. Whereas this report focuseson the geoscience of climate change, subsequent working groups, whose work will be published in 2014, will focus on other aspects of the science as well as mitigation.
The report reaffirms that the human influence on the planet's dramatic warming is clear and beyond reproach. According to a press statement accompanying the release of the report:
It is extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century. The evidence for this has grown, thanks to more and better observations, an improved understanding of the climate system response and improved climate models.
Thomas Stocker, Co-Chair of the working group behind the report indicated that in order to prevent the worst case scenarios presented in the report for the century ahead, governments will need to take aggressive action. "Continued emissions of greenhouse gases will cause further warming and changes in all components of the climate system," Stocker said. "Limiting climate change will require substantial and sustained reductions of greenhouse gas emissions."
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The IPCC document—officially labeled as IPCC Working Group I assessment report (AR5) and titled Climate Change 2013: the Physical Science Basis—was approved by the world scientific body on Friday in Stockholm and is the panel's official statement—made after hundreds of the world's top scientists reviewed thousands of studies—on climate change, ocean and atmospheric temperatures, and global warming.
“As the ocean warms, and glaciers and ice sheets reduce, global mean sea level will continue to rise, but at a faster rate than we have experienced over the past 40 years,” said Dahe.
And its other key findings are startling. They include:
- Warming of the climate system is unequivocal, and since the 1950s, many of the observed changes are unprecedented over decades to millennia. The atmosphere and ocean have warmed, the amounts of snow and ice have diminished, sea level has risen, and the concentrations of greenhouse gases have increased.
- Each of the last three decades has been successively warmer at the Earth’s surface than any preceding decade since 1850. In the Northern Hemisphere, 1983–2012 was likely the warmest 30-year period of the last 1400 years (medium confidence).
- Ocean warming dominates the increase in energy stored in the climate system, accounting for more than 90% of the energy accumulated between 1971 and 2010 (high confidence). It is virtually certain that the upper ocean (0−700 m) warmed from 1971 to 2010, and it likely warmed between the 1870s and 1971.
- Over the last two decades, the Greenland and Antarctic ice sheets have been losing mass, glaciers have continued to shrink almost worldwide, and Arctic sea ice and Northern Hemisphere spring snow cover have continued to decrease in extent (high confidence).
- The rate of sea level rise since the mid-19th century has been larger than the mean rate during the previous two millennia (high confidence). Over the period 1901–2010, global mean sea level rose by 0.19 [0.17 to 0.21] m.
- The atmospheric concentrations of carbon dioxide (CO2), methane, and nitrous oxide have increased to levels unprecedented in at least the last 800,000 years. CO2 concentrations have increased by 40% since pre-industrial times, primarily from fossil fuel emissions and secondarily from net land use change emissions. The ocean has absorbed about 30% of the emitted anthropogenic carbon dioxide, causing ocean acidification.
- Total radiative forcing is positive, and has led to an uptake of energy by the climate system. The largest contribution to total radiative forcing is caused by the increase in the atmospheric concentration of CO2 since 1750.
- Human influence on the climate system is clear. This is evident from the increasing greenhouse gas concentrations in the atmosphere, positive radiative forcing, observed warming, and understanding of the climate system.
“The world’s scientists have spoken," said Sarah-Jayne Clifton, climate justice and energy coordinator for Friends of the Earth International, in reaction to the report. Clifton said the report once again reaffirms "now with absolute certainty" that climate change is caused by humans and "that it poses a severe and immediate threat to our future and that of the planet."
"Communities around the world are already being devastated by extreme weather. It is untenable for our political leaders to continue their inaction," she said. "The interests of humanity must be prioritized above the profits of dirty energy corporations through an urgent and dramatic transformation of the world’s corporate-controlled, unsustainable energy system."
As details of the report were being digested by the world community, responses to it were trending on Twitter: