A lake formed from melt water from the Pastoruri glacier, as seen from atop the glacier in Huaraz, September 19, 2013. The nearby Pastoruri glacier is one of the fastest-receding glaciers in the Cordillera Blanca mountain range, according to a 2012 paper by the University of Texas and the Huascaran National Park. (Reuters/Mariana Bazo)
One of the most comprehensive scientific reviews ever assembled confirms what most people already acknowledge about climate change: it is happening, human activity is causing it, and we have a rapidly closing window of time to prevent unprecedented, potentially catastrophic climatic shifts.
What the Intergovernmental Panel of Climate Change report summary released this morning in Stockholm adds is near-certainty that warming is man-made, and stronger language to describe the changes underway.
Global warming is “unequivocal,” and its effects “unprecedented over decades to millennia,” states the IPCC, which considered the research of some 600 scientists from thirty-two countries, and concluded that there are more greenhouse gases in the atmosphere now than at any point in at least 800,000 years. “It is extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century,” states the report. Fossil fuel emissions and to a lesser extent land-use changes account for a 40 percent increase in carbon dioxide concentrations since pre-industrial times.
According to the IPCC, the atmosphere can absorb no more than 1 trillion tons of carbon dioxide without warming exceeding 2 degrees Celsius, the threshold scientists have agreed is crucial to stay below in order to prevent the most catastrophic effects of climate change. More than half of that carbon dioxide has already been emitted, and the world is on track to pump out the rest within 40 years, The New York Times reports. (Other models suggest we have even less time.)
Climate change is not only unprecedented but also “irreversible on a multi-century to millennial time scale.” Even if no new greenhouse gasses were added to the atmosphere, temperatures will stay high for centuries. And don’t count on geoengineering to save the planet. Proposed solutions like sucking carbon out of the atmosphere or spraying sulfur into the air to block sunlight face “biogeochemical and technological limitations,” and, in the case of solar radiation management, would “modify the global water cycle, and would not reduce ocean acidification.”
The report is the strongest show yet of the scientific consensus on the occurrence and implications of anthropogenic climate change, but it is unlikely to stir up any political action in proportion to the science. “This is science, these are facts, and action is our only option,” Secretary of State John Kerry said in a statement in response to the report. The report’s near-certainty in linking human activity to climate change is striking in light of the fact that the 1990 report did not quantify the human contribution at all, and the 1995 report pointed only to a “discernable human influence on climate.”