Skip to main content

Climate change report: It's 'extremely likely' that humans are responsible

By Brandon Miller, CNN
September 27, 2013 -- Updated 1412 GMT (2212 HKT)
STORY HIGHLIGHTS
  • 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.

A recent study published in the science journal "Nature" has concluded that many more trees are vulnerable to drought stress than previously thought. A majority of trees studied operate very close to their hydraulic threashold, taking on just enough water to survive. A recent study published in the science journal "Nature" has concluded that many more trees are vulnerable to drought stress than previously thought. A majority of trees studied operate very close to their hydraulic threashold, taking on just enough water to survive.
Is climate change moving too fast for trees?
HIDE CAPTION
<<
<
1
2
3
4
5
6
>
>>
Saving the coral reefs
Scottish salmon fisheries imperiled

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."

Beneath Greenland's ice, a grand canyon

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.

While 90% constitutes a "very likely" degree of certainty, Friday's report stating scientists are now 95% sure indicates an "extremely likely" degree of certainty, which is considered the gold standard when discussing probability.

The effects humans 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.

Bloomberg: Why Sandy forced cities to take lead on climate change

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.

Climate change may increase violence, study shows

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.

Climate sticker shock: Arctic thaw could cost $60 trillion

ADVERTISEMENT
Part of complete coverage on
September 22, 2014 -- Updated 2001 GMT (0401 HKT)
The U.S. has promised to supply and train "acceptable" rebels in Syria to counter ISIS. But who are they and are can the strategy work?
September 23, 2014 -- Updated 0257 GMT (1057 HKT)
Do the Chinese really like to mix their Bordeaux with Coca-Cola?
September 23, 2014 -- Updated 0938 GMT (1738 HKT)
Al Qaeda's new Syrian branch, Khorasan, is seeking new ways to attack America and Europe, with a top U.S. intelligence official saying it has "aspirations for attacks on the homeland."
September 23, 2014 -- Updated 0039 GMT (0839 HKT)
Branded an "extremist" by China's state-run media, Joshua Wong isn't even old enough to drive.
September 22, 2014 -- Updated 0655 GMT (1455 HKT)
Indian Prime Minister Narendra Modi surprised political pundits with his rapid rise to power. CNN meets the man behind the enigma.
September 22, 2014 -- Updated 1144 GMT (1944 HKT)
Liverpool's Italian forward Mario Balotelli reacts during the UEFA Champions League Group B match between Liverpool and Ludogorets Razgrad at the Anfield stadium in Liverpool on September 16, 2014.
British police launched an investigation into abusive tweets sent to Liverpool striker Mario Balotelli.
September 21, 2014 -- Updated 2344 GMT (0744 HKT)
A woman who was texting her husband before he was killed reflects on the Westgate attack.
September 22, 2014 -- Updated 1554 GMT (2354 HKT)
The real secret to a faster commute has been with us all along -- the bus.
September 22, 2014 -- Updated 1316 GMT (2116 HKT)
13 brands retained their Top 20 status from last year, according to an annual survey.
September 22, 2014 -- Updated 1549 GMT (2349 HKT)
Think your new tattoo is cool? Look at how our ancestors did it and think again.
September 22, 2014 -- Updated 1100 GMT (1900 HKT)
Each day, CNN brings you an image capturing a moment to remember, defining the present in our changing world.
Browse through images from CNN teams around the world that you don't always see on news reports.
ADVERTISEMENT