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September 20, 2013

Report Expected to Highlight Human Causes of Climate Change

by Rosanne Skirble

The Intergovernmental Panel on Climate Change (IPCC) brings together hundreds of the world’s leading scientists to study the effects of human activity on the Earth’s climate, the impact of climate change on the environment and civil society and ways to mitigate its effects.

Since 1990 the IPCC has issued four assessments; the fifth is due out Friday, September 27. The IPCC reports help governments and civil society make more informed decisions on climate issues.

The IPCC Fifth Assessment Report will be released in stages over the next year, beginning with an analysis of the physical science of climate change. The report is a consensus of how and why the climate is changing and how it might change in the future.

“It will look at changes in the temperature of the atmosphere and oceans, changes in storms, rainfall patterns, droughts, and other extreme weather events, and the consequences of changes in glaciers and ice sheets for sea level rise," said Alden Meyer, a policy analyst for the Union of Concerned Scientists. "It will also assess the contributions to these changes from both human activities and natural factors.”

The report synthesizes peer-reviewed studies on climate change science released since the last IPCC report in 2007. It is an immense task that has engaged hundreds of authors, editors and reviewers from 47 countries. Meyer doesn’t expect any startling new findings.

“But it will validate and reinforce the findings of previous IPCC reports with probably an increased level of confidence in some areas,” Meyer said.  
    
James McCarthy played a lead role in the Third IPCC Assessment Report released in 2001. The Harvard oceanographer says that since the fourth report, climate science has advanced significantly. Much more is known, for example, about the heat content of the ocean, he says, as reflected in data from an immense array of floats in the world’s oceans.

“The ocean heat content has been steadily increasing over the last 20 years and although earlier data would have allowed us to make a statement like that, the precision, coming from these 3500 floats, allows us to say this with much greater confidence," McCarthy said.

Also, McCarthy adds, a lot more is now known about the accelerated loss of ice from Greenland and Antarctica, and the projection of sea level rise connected to that loss.  

“If the ice melts on Greenland and Antarctica, how much will sea level rise? We’ll see now in the calculations for projected sea level rise that we didn’t see in 2007," he said. "So this will be a big improvement for people who are indeed looking with increasing concern at what might happen in coastal areas.”  

A draft version of the report leaked to the media last month states that the planet has warmed at a rapid pace since the 1950s and that it is extremely likely, 95 percent likely, that humans caused more than half of the observed changes, including melting snow and ice, sea level rise and climate extremes.
        
Climatologist Heidi Cullen with the non-profit group Climate Central says if that degree of certainty remains in the language of the report it will be significant.

“I think that with this report coming out, a statement like 95 percent certainty that human influence on climate is a result of our actions, that statement in and of itself, is quite profound," Cullen said. "We have altered the planet. Our actions have altered the planet, and we’re about as precise as you can get, as confident as you can get in that."

The Fifth Assessment Report will be released on Sept. 27 in Stockholm, followed by reports in 2014 on the impact of climate change and what can be done about it.