A report issued on Friday, Sept. 27 by a working group of the Intergovernmental Panel on Climate Change (IPCC) essentially confirms the conclusions drawn by previous reports that human activities, especially the burning of fossil fuels, are largely responsible for climate change.
Working Group 1’s “Contribution to the IPCC Fifth Assessment Report Climate Change 2013: The Physical Science Basis Summary for Policymakers” is a 36-page summary of the science component of the IPCC’s Fifth Assessment Report that notes that “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.” The full report runs 2,216 pages.
Without saying there is 100% “consensus,” the report summary does say that “It is virtually certain that globally the troposphere has warmed since the mid-20th century. More complete observations allow greater confidence in estimates of tropospheric temperature changes in the extratropical Northern Hemisphere than elsewhere. There is medium confidence in the rate of warming and its vertical structure in the Northern Hemisphere extra-tropical troposphere and low confidence elsewhere.”
The summary says that “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.” Elsewhere, it concludes that “Human influence has been detected in warming of the atmosphere and the ocean, in changes in the global water cycle, in reductions in snow and ice, in global mean sea level rise, and in changes in some climate extremes. . . . This evidence for human influence has grown since AR4. It is extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century.”
In what appears to be a response to critics who took issue with the IPCC’s previous climate models, the summary comments that “Climate models have improved since the AR4. Models reproduce observed continental-scale surface temperature patterns and trends over many decades, including the more rapid warming since the mid-20th century and the cooling immediately following large volcanic eruptions (very high confidence).”
Looking ahead, the working group concludes that “Continued emissions of greenhouse gases will cause further warming and changes in all components of the climate system. Limiting climate change will require substantial and sustained reductions of greenhouse gas emissions.”
U.S. Energy Secretary Ernest Moniz said the panel’s summary report underscores the need for President Obama’s Climate Action Plan.
As has been the case with every previous IPCC report, fossil fuel industry groups and “climate skeptics” have lined against, while most groups associated with environmental concerns and renewable and nuclear generation applaud it, which indicates that positions on the issue have become so entrenched, particularly in the U.S., that no amount of carefully worded prose presenting any amount of scientific research and data analysis is likely to alter those positions.
In China, currently the largest GHG emitter and a country affected by sea level changes—just one factor contributing to that nation’s plan to reduce GHG emissions 17% below 2005 levels—the response has been to accept the IPCC findings. And in Australia, The Australian newspaper quoted Environment Minister Greg Hunt as saying that the report’s findings reinforced the government’s “bipartisan support for the science and the targets set for emissions reductions.” Like the U.S., Australian politics over fossil fuel use and GHG emission limits have been contentious.
—Gail Reitenbach, PhD (@POWERmagazine, @GailReit)