The Earth has changed in “unprecedented ways” since 1950, the U.N. says, and its scientists are 95 percent certain that humans are responsible.
Yet the planet has largely stopped warming over the past 15 years, data shows -- and a landmark report released Friday by the U.N.’s climate group could not explain why the mercury has stopped rising.
Global surface temperatures rose rapidly during the 70s, but have been relatively flat over the past decade and a half, rising only 0.05 degrees Celsius (0.09 degrees Fahrenheit) per decade according to data from the U.K.’s weather-watching Met Office, a trend current models of the world’s climate have been unable to predict. A draft of the report leaked in early September acknowledged that trend and put it bluntly: We simply can’t explain it.
“Models do not generally reproduce the observed reduction in surface warming trend over the last 10–15 years.”
But a final version of the report released Friday morning by the U.N.’s Intergovernmental Panel on Climate Change (IPCC) strips out the failure of models and explains away the downward trend.
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“Due to natural variability, trends based on short records are very sensitive to the beginning and end dates and do not in general reflect long-term climate trends,” the new report reads.
A later reference suggests volcanoes, oceans and solar activity may have affected the warming, although the IPCC said it wasn't confident in that finding.
The U.N. arm also acknowledges another possibility: Maybe it was wrong.
"There may also be ... an overestimate of the response to increasing greenhouse gas and other anthropogenic forcing," the new report admits.
Climate skeptics have seized upon the change in world weather patterns, some citing it as evidence that global warming itself has decelerated or even stopped. Benny Peiser, director of the Global Warming Policy Foundation, said the slowdown was a far larger issue than the report shows.
“Unless global temperature will begin to rise again in the next few years, the IPCC is very likely going to suffer an existential blow to its credibility,” he said. Judith Curry, professor and chair of the School of Earth and Atmospheric Sciences at the Georgia Institute of Technology, was even blunter.
“IPCC has thrown down the gauntlet – if the pause continues beyond 15 years (well it already has), they are toast.”
Many governments had objections over how the issue was treated in earlier drafts and some had called for it to be deleted altogether. In a Friday morning presentation of its findings, Thomas Stocker, co-chair of the group that wrote the report, defended that decision, the Associated Press reported.
"An old rule says that climate-relevant trends should not be calculated for periods less than around 30 years," Stocker said.
Many scientists say the slowdown reflects 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.
Stocker said there wasn't enough literature on "this emerging question."
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, co-chair of the working group that wrote the report.
Yet recent reports have stressed that climate models have failed to accurately predict global temperatures. A study in the journal Nature Climate Change compared 117 climate predictions made in the 1990's to the actual amount of warming. Out of 117 predictions, the study’s author told FoxNews.com, 3 were roughly accurate and 114 overestimated the amount of warming.
On average, the predictions forecasted two times more global warming than actually occurred.
"It's a real problem ... it shows that there really is something that needs to be fixed in the climate models," climate scientist John Christy, a professor at the University of Alabama in Huntsville, told FoxNews.com at the time.