STOCKHOLM (AP) — Scientists now believe it’s “extremely
likely” that human activity is the dominant cause of global warming, a long-term
trend that is clear despite a recent plateau in the temperatures, an
international climate panel said.
The Intergovernmental Panel on Climate Change used its
strongest language yet in a report on the causes of climate change, prompting
calls for global action to control emissions of carbon dioxide and other
“If this isn’t an alarm bell, then I don’t know what one is.
If ever there were an issue that demanded greater cooperation, partnership and
committed diplomacy, this is it,” said U.S. Secretary of State John Kerry.
The IPCC, which has 195 member countries, adopted the report
after all-night talks at a meeting in Stockholm.
In its previous assessment, in 2007, the U.N.-sponsored
panel said it was “very likely” that global warming was due to human activity,
particularly the carbon dioxide emissions resulting from the burning of coal,
oil and gas.
The change means that scientists have moved from being 90
percent sure to 95 percent — about the same degree of certainty they have that
“At 90 percent, it means there is a 10 percent probability
that it’s not entirely correct,” said Chris Field, Carnegie Institution
scientist who is a leader in the IPCC, but wasn’t involved in writing the
report. “And now that’s 5 percent. So it’s a doubling of our confidence. That’s
actually a consequential change in our level of understanding.”
One of the most controversial subjects in the report was how
to deal with what appears to be a slowdown in warming when temperature data for
the past 15 years is examined. Climate skeptics said this “hiatus” casts doubt
on the scientific consensus on climate change, even though the past decade was
the warmest on record.
Many governments had objections over how the issue was
treated in earlier drafts and some had called for it to be deleted altogether.
In the end, the IPCC made only a brief mention of the issue
in the summary for policymakers, emphasizing that short-term records are
sensitive to natural variability and don’t in general reflect long-term trends.
“An old rule says that climate-relevant trends should not be
calculated for periods less than around 30 years,” said Thomas Stocker, co-chair
of the group that wrote the report.
Many scientists say the temperature data reflect random
climate fluctuations and an unusually hot year, 1998, picked as a starting point
for charting temperatures. Another leading hypothesis is that heat is settling
temporarily in the oceans, but that wasn’t included in the summary.
Stocker said there wasn’t enough literature on “this
The IPCC said the evidence of climate change has grown
thanks to more and better observations, a clearer understanding of the climate
system and improved models to analyze the impact of rising temperatures.
“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, the other co-chair of the working group.
The full 2,000-page report contained few surprises, as many
of the findings had been leaked in advance.
As expected, the IPCC raised its projections of the rise in
sea levels to 10 to 32 inches by the end of the century. The previous report
predicted a rise of 7 to 23 inches.
But it did acknowledge that the climate may be less
sensitive to carbon dioxide emissions than was stated in 2007. Back then, the
IPCC said that a doubling of carbon dioxide concentrations in the atmosphere
would likely result in 3.6 to 8.1 degrees of warming. This time it restored the
lower end of that range to what it was in previous reports, 2.7 degrees.
The IPCC assessments are important because they form the
scientific basis of U.N. negotiations on a new climate deal. Governments are
supposed to finish that agreement in 2015, but it’s unclear whether they will
commit to the emissions cuts that scientists said will be necessary to keep the
temperature below a limit at which the worst effects of climate change can be
Using four scenarios with different emissions controls, the
report projected that global average temperatures would rise by 0.5 to 8.6
degrees this century.
Only the lowest scenario, which was based on major cuts in
carbon dioxide emissions and is considered unlikely, came in below limit that
countries have set as their target in the climate talks to avoid the worst
impacts of warming. That limit is a warming of 3.6 degrees compared with before
the industrial revolution in the 18th century.
At this point, emissions keep rising mainly due to rapid
growth in China and other emerging economies. But those nations say rich
countries should take the lead on emissions cuts because they’ve pumped carbon
into the atmosphere for longer.
Climate activists said the report should spur governments to
“There are few surprises in this report, but the increase in
the confidence around many observations just validates what we are seeing
happening around us,” said Samantha Smith, of the World Wildlife Fund.
The report deals with the physical science of climate
change. Next year, the IPCC will adopt reports on the impacts of global warming,
strategies to fight it and a synthesis of all three reports.
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