Top World Stories - Climate change report: It's 'extremely likely' that humans are responsible

Scientists are 95% certain that human activity has caused at least half of climate change in the last 50 years, a U.N. report concludes. FULL STORY

By Brandon Miller, CNN
September 27, 2013 -- Updated 1256 GMT (2056 HKT)
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Understanding the climate change report

STORY HIGHLIGHTS
  • NEW: Climate change deniers beware, says Secretary of State John Kerry
  • There is even more certainty that humans are playing a role
  • The report lays out projections for climate change through the end of the century
  • The first section of the report is aimed at assisting policymakers
(CNN) -- Human activity has caused at least half of climate change in the last half-century, hundreds of scientists say. They are 95% certain of this, the surest they've ever been, says a United Nations report published Friday.
That activity? Driving cars, running power plants on coal and oil, torching swathes of forestland and debris; anything involving burning carbon-based fuels and emitting greenhouse gases.
We are seeing the consequences already in extreme weather patterns, particularly drought and flood, and they will probably get worse this century, the report said.
"It should serve as yet another wake-up call our activities today have a profound impact on society, not only for us, but for many generations to come," Michel Jarraud, head of the World Meteorological Organization, said at a news conference in Stockholm, Sweden.
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U.S. Secretary of State John Kerry echoed his words in an official statement.
"Those who deny the science or choose excuses over action are playing with fire," he said. "Once again, the science grows clearer, the case grows more compelling, and the costs of inaction grow beyond anything that anyone with conscience or common sense should be willing to even contemplate."
The assessment report from the Intergovernmental Panel on Climate Change is the benchmark study on global warming published every few years. Nearly 1,000 researchers from around the world work on the document, which then undergoes review by about as many scientists.
The panel released a summary report Friday and plans to post the full version, roughly 2,500 pages, online on Monday.
This year's report further strengthens the suspicions that scientists already have.
In 2007, climate researchers were already 90% sure that people were behind a seemingly small rise in global average temperature of about half a degree Celsius (1 degree Fahrenheit) that has already notched up extreme weather events such as heat waves, droughts and flooding.
The effects they are already causing are expected to increase for a century or more, the report reads. Weather catastrophes, previously called storms of the century, are on their way to striking every 20 years or even more frequently.
This means, unfortunately, that we could see more EF5 tornadoes like the one that ground up Moore, Oklahoma; stronger and more floods like those that inundated Colorado towns; another Sandy or Katrina or two in our lifetimes; more crops wiped out by drought; and more forestland consumed by roaring wildfires.
The Arctic ice cap could melt nearly completely in summer, and sea levels could continue to rise. In the Antarctic, the ice cap could continue to increase slightly.
And if greenhouse gas emissions continue to climb as they have, the resulting temperature rise and its deadly effects would get even worse, the report says.
Hundreds of experts weigh in
The 2013 assessment report from the Intergovernmental Panel on Climate Change brings together the latest research from top scientists in the field. It contains a "summary for policymakers" aimed at guiding politicians and lawmakers worldwide on decisions regarding the environment over the next several years.
The document released Friday explains the physical science behind climate change.
The U.N. panel releases a report every five or six years. Friday's report is the culmination of work by more than 250 authors from 39 countries and was subject to an extensive review process involving more than 1,000 experts.
More than 850 expert authors from 85 countries contributed research for the full report, which will be released in three stages through April. The first, on the physical science behind climate change, accompanies the summary for policymakers. The second, expected in March, will cover "impacts and vulnerabilities" of climate change; the third, on mitigation efforts, is set to go out in April.
Critics of the report
Despite the breadth of the scientific expertise involved and the extensive review and approval process, the assessment reports spark quite a few criticisms, from both climate change believers and skeptics.
Skeptics say the panel exists only to produce further evidence supporting the idea of man-made climate change while ignoring opposing research. But climate change activists, and many climate scientists, say the panel's consensus-seeking policy produces conclusions and estimates that are too conservative.
Another often-cited critique of the report is that, due to its size and lengthy approval process, it is already outdated by the time it is released. Several important studies already have been published in the past year in the constantly evolving science of climate change that will not be included in this assessment.
Despite the critics, this week's document will serve as a major measuring stick for the current state of the world's climate and what type of change is in store.
The summary for policymakers will be available Friday at www.climatechange2013.org.
September 27, 2013 -- Updated 1300 GMT (2100 HKT)
A U.N. climate panel says in its latest report that it is more confident than ever that humans are responsible for at least half of temperature increases since the 1950s. FULL STORY

 

U.N. climate change report points blame at humans

By Dave Hennen, Brandon Miller and Eliott C. McLaughlin
September 27, 2013 -- Updated 0936 GMT (1736 HKT)
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U.N. climate report blames humans

STORY HIGHLIGHTS
  • Scientists surer than ever humans play major role in climate change, report says
  • Global warming already affecting extreme weather, and it could get worse, report says
  • U.N.'s IPCC convenes every six years to put together report; it's considered benchmark on topic
  • Even if emissions ended today, effects of climate change could linger for centuries
(CNN) -- The world's getting hotter, the sea's rising and there's increasing evidence neither are naturally occurring phenomena.
So says a report from the U.N. International Panel on Climate Change, a document released every six years that is considered the benchmark on the topic. More than 800 authors and 50 editors from dozens of countries took part in its creation.
The summary for policymakers was released early Friday, while the full report, which bills itself as "a comprehensive assessment of the physical science basis of climate change," will be distributed Monday. Other reports, including those dealing with vulnerability and mitigation, will be released next year.
Here are the highlights from Friday's summary:
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Climate scientists are 95% confident -- that is to say, surer than ever -- that humans are responsible for at least "half of the observed increase in global average surface temperatures since the 1950s."
This is the major headline from the report, as it marks a stark spike in confidence over the last 12 years, as scientists were 90% confident in 2007 and 66% confident in 2001 of the same conclusion.
An increase in carbon dioxide concentrations that is "unprecedented" in the last 20,000 years, along with increases in other emissions, have driven up average temperatures by about 0.6 degrees Celsius (1 degree Fahrenheit) since 1950, the report states.
Worst-case predictions are that by 2100, temperatures could increase by as much as 3.7 degrees Celsius (6.6 Fahrenheit), the report says.
Climate change is already affecting extreme weather
Since 1950 we've seen a dramatic increase in extreme weather. This is especially true of record heat and heavier precipitation events.
While it's difficult to determine the exact role climate change plays in an individual event, such as Hurricane Sandy or the EF-5 tornado that struck Moore, Oklahoma, because there are so many ingredients necessary to brew a single storm, the links are clearer when you look at overall patterns.
According to a study released this month in the Bulletin of the American Meteorological Society, scientists found strong links between global warming and extreme weather around the globe in 2012.
Among the 2012 events were the July heat wave in the northeastern and north-central United States, the spring heat wave in the eastern United States, the Great Plains drought, the winter drought in Spain and Portugal and the heavy rains and flooding in Europe.
According to a paper in the journal Nature, this year, weather events that have previously been classified as "storms of the century" could become the storm of "every 20 years or less."
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"Climate change will probably increase storm intensity and size simultaneously, resulting in a significant intensification of storm surges," the paper said.
The last 30-year period is "very likely" the warmest in the last 800 years
Scientists are 90% sure that 1981-2010 was the warmest such span in the last eight centuries, and there's a 66% chance that it was the warmest 30-year period in the last 1,400 years.
While the last 15 years have not warmed as quickly, we've seen steady warming over most of the globe, and we haven't seen a below-average temperature month since February 1985.
Scientists are also 99% certain that we will see more hot days and nights -- and fewer chilly ones -- as the 21st century progresses.
"Each of the last three decades has been significantly warmer than all preceding decades since 1850," according to the IPCC report.
To give you an idea of how the Earth has heated up, the combined land and ocean temperature increased by about 0.8 degrees Celsius between 1901 and 2010, yet between 1979 and 2010, the temperature spiked about 0.5 degrees Celsius.
Sea level rise will increase due to warming oceans and loss of ice
Better climate models give scientists more confidence that sea level rise will accelerate in the 21st century.
Scientists are 99% sure that sea level rise has accelerated over the last 2 centuries at a rate higher than at any time in the last 2,000 years.
They're also highly confident that if the global surface temperature increases by more than 2 degrees Celsius over present temperatures we could see "a nearly ice-free Arctic Ocean in late summer."
The report further notes that there is increasing evidence that ice sheets are losing mass, glaciers are shrinking, Arctic sea ice cover is diminishing, snow cover is decreasing and permafrost is thawing in the Northern Hemisphere.
As for the rise in sea level, scientists asserted in the IPCC report that tide gauges and satellite data make it "unequivocal" that the world's mean sea level is on the upswing.
Even if we end emission tomorrow, climate change could continue for centuries
This may be one of the more harrowing findings in the report, as it suggests we're too far gone to effect any meaningful change in our lifetimes.
Even if we end carbon dioxide emissions today, effects could linger for hundreds, if not thousands, of years. And certain changes may already be irreversible.
"Many aspects of climate change will persist for centuries even if concentrations of greenhouse gases are stabilized. This represents a multicentury commitment created by human activities today," the report states.
COPY  http://edition.cnn.com/

 

 

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