Climate change: Scientists now 95 percent certain we are mostly to blame
A draft summary prepared for the Intergovernmental Panel on Climate Change says that more than half of global warming is caused by human emissions of greenhouse gases.
Since 1951, Earth's climate has warmed by about 0.6 degrees Celsius, and researchers assessing the state of climate science for the Intergovernmental Panel on Climate Change (IPCC) are 95 percent certain that more than half of the warming is due to human emissions of greenhouse gases.Skip to next paragraph
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The statement is one conclusion in the final draft of a summary the IPCC is preparing for world policymakers on the state of the climate and climate science as part of its fifth assessment report on global warming.
The IPCC will release the full four-volume set and related summaries beginning at the end of September and into next year. The other volumes deal with current and projected effects of climate change.
The summary on climate and climate science will get word-by-word scrutiny at a meeting in Stockholm Sept. 23-26 as politicians and scientists arm-wrestle over the final text.
In the meantime, it gives clear insights into what scientists see happening to the planet's climate as human industrial activities, as well as land-use changes, pump increasing amounts of carbon dioxide and other greenhouse gases into the air.
In some areas, certainty over what is happening has increased since the IPCC published its last set of reports in 2007. Certainty over the human role has increase from "very likely" to "extremely likely," a verbal shift representing 90 percent certainly in 2007 to 95 percent for this round of reports.
The draft notes that despite the relentless build-up of greenhouse gases in the atmosphere, the rate of warming over the past 15 years has been small compared with warming between 1951 and 2012, suggesting that within an overall warming that began in the first decade of the 1900s, the climate system still displays substantial variability on time scales of a decade or so.
When the increases in the atmospheric concentrations of CO2 are combined with those of other greenhouse gases, such as methane and nitrous oxide, the overall concentrations are the highest in at least 800,000 years. The current rates of increase in these gases "are unprecedented in the last 22,000 years," the draft states.
The recent pause in the rate of increase in warming has left researchers scurrying to unravel the mystery. The upper layers of the earth’s oceans are a lead suspect for absorbing more heat that otherwise would remain in the atmosphere.
Still, each of the past three decades have been warmer than all of the previous decades since the mid-1850s, when regular record-keeping began, the draft says. The first decade of this century topped them all. The past 30 years have "very likely" been the warmest in the past 800 years, and "likely" the warmest three decades in the past 1,400 years.
The IPCC reports represent scientific time capsules. They provide an overview of the state of the science, but the research is more than a year old by the time the volumes hit the streets. Because these reports are influential, this lag has led to criticisms that their conclusions can be too conservative.