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International report says humans almost certainly cause global warming

A panel of the world’s leading climate scientists strongly asserted yesterday that “it is extremely likely that human influence has been the dominant cause” of global warming since 1950, and warned of more rapid ice melt and rising seas if governments do not aggressively act to reduce the pace of greenhouse gas emissions.

At a meeting in Stockholm, where the panel released its latest assessment of climate change, the scientists for the first time established a budget for the amount of carbon that can be released into the atmosphere. Even if that goal is reached, carbon emissions will have a harmful impact on the environment well into the future.

“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 Qin Dahe, a Chinese scientist who co-chaired the working group that produced the first of the report’s three segments.

“As a result of our past, present and expected future emissions of (carbon dioxide), we are committed to climate change, and effects will persist for many centuries even if emissions . . . stop,” said Thomas Stocker, a German scientist who served as the other co-chair of the group.

The 2,000-page report of the Intergovernmental Panel on Climate Change (IPCC), appointed by the United Nations, will not be available until Monday, following a weekend of editing and corrections. But a summary highlighting 20 findings was provided early yesterday.

Some key findings were that the planet is warming at an accelerated pace without any doubt, that humans are causing it with 95 percent certainty and that the past three decades have been the hottest since 1850.

Carbon concentrations in the atmosphere have increased 40 percent since that time, and “combined atmospheric concentrations of carbon dioxide, methane, and nitrous oxide have increased to levels unprecedented in at least the last 800,000 years.”

In the past two decades, the Greenland and Antarctic ice sheets have steadily lost mass, and glaciers are shrinking across the world. The rate of sea-level rise since the mid-19th century has been higher than the rate of the past two millennia.

The panel expressed high confidence in its findings because climate models that help scientists observe surface temperature patterns have improved in the past six years, since its previous climate assessment. The current assessment is the IPCC’s fifth since 1990.

Critics have called climate models that the IPCC and other climate scientists rely on into question, saying they have not taken a 15-year global warming slowdown into greater account.

But scientists on the panel said their report gives greater weight to evidence of warming over a much longer period. “Certainly if we experience ⅛a slowdown⅜ for the next 20 years, we cannot be confident in the models,” Stocker said at the Stockholm meeting, aired via a webcast.

On the other hand, he said: “The last three decades were the warmest in the last 150 years. The present decade indeed is the warmest one.” Stocker said a 15-year variable in the temperature will be taken into account by scientists in coming years.

Using four scenarios based on different controls on greenhouse gas emissions, the report projected a rise in temperatures ranging from less than one degree to nearly nine degrees.

The two lowest scenarios could happen only with steep cuts in carbon emissions among developed nations, particularly China and the United States, the world’s leading polluters. The Obama administration recently acted to curb emissions of future coal- and gas-fired power plants.

Only the lowest scenario based on significant carbon emission cuts is likely to meet the limit of 3.6 degrees Fahrenheit above pre-industrial temperatures agreed upon by IPCC member nations. That would avoid the worst warming impacts.

For the first time, the report provided a carbon budget of 1 trillion tons of carbon released in the atmosphere to avoid the worse affects of climate change. More than half that amount has already been released. Up to 3 trillion tons are buried in the Earth as fossil fuel.

In the United States, officials reacted favorably to the report. Secretary of State John F. Kerry said that “climate change is real” and that the United States is determined to be a leader in curbing emissions.

Sen. Barbara Boxer, D-Calif., chair of the Committee on Environment and Public Works, called the report a landmark and said it underscores the administration’s recent efforts. “I will do everything in my power to support the administration in their efforts to address the dangerous impacts of climate disruption,” Boxer said.

Frances Beinecke, president of the Natural Resources Defense Council, an environmental advocacy group, called the report “a warning bell to the world.” She said the impacts are fierce wildfires, drought, floods and storms that will get worse with delay. “The science is clear: We are altering the climate,” Beinecke said.

But deniers of climate change dismissed the report. Anthony Watts, a former television meteorologist who writes the blog Watts Up With That?, called it “comical at best.”

Watts said on his blog that IPCC models “fail to model reality, and this has been pointed out worldwide in media, it becomes a ‘jump the shark’ moment where the advocacy speaks far louder than the science.”

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