Scientists declare: 'Human activities are changing Earth's climate'

Image: Coal-fired power plant.
A 2011 photo shows a coal-fired power station in Huaibei, in east China's Anhui province. In a declarative statement, a prominent science organization linked human activities such as burning fossil fuels to climate change.

With more confidence than ever before, a prominent scientific body put the blame for global climate change squarely at the feet of humanity's insatiable appetite for fossil fuels, which release heat-trapping gases when burned. 

"There is only one thing that is going straight up … that is the greenhouse gases that we are just pumping at an exponential rate," Gerald North, an atmospheric scientist at Texas A&M University who chaired the committee responsible for the statement, told NBC News.

The statement was released Monday by the American Geophysical Union, a more than 62,000-member-strong organization of Earth and space scientists who come from 144 countries. The non-profit traditionally renews its position statements every four years.

The latest revision uses the most declarative language yet, illustrating increased confidence that human activity is responsible for most of the observed warming of 1.5 degrees Fahrenheit over the past 140 years.

"Human activities are changing Earth's climate," the 537-word statement begins, going on to add that "extensive, independent observations confirm the reality of global warming." Among the observations cited are warming air and sea temperatures, melting glaciers and rising seas. 

All of the observations are consistent with physics and predictions of how the climate should change in response to increasing greenhouse gas emissions, and they're "inconsistent with explanations of climate change that rely on known natural influences," the 15-member committee writes.

The committee said society will face unavoidable consequences from climate change, but there is time to lessen the impacts.

"Actions to diminish the threats posed by climate change to society and ecosystems include substantial cuts to emissions to reduce the magnitude of climate change, as well as preparing for changes that are now unavoidable," the statement says.

One committee member, Roger Pielke Sr., a retired professor of atmospheric sciences at Colorado State University (and father of frequently quoted climate scientist Roger Pielke Jr. at the University of Colorado), dissented from the statement. 

In reply to a request for comment, the elder Pielke directed NBC News to a response provided to Climate Etc., a blog hosted by Georgia Tech climate scientist Judith Curry. Among his criticisms of the statement is what he called an inaccurate "view of climate change that is dominated by the emission of (carbon dioxide) and a few other greenhouse gases" rather than the full complexity of the issue and its uncertainties.

He provided Curry with his own proposed text, which he said is more balanced and "scientifically robust." Curry said she preferred Pielke's response, but questioned "why the AGU or any other professional society is issuing statements on this topic," adding that it is "an explicit statement of advocacy."

Crafting the statement, North said, was anything but easy. Drafts went back and forth among committee members for months, with constant wrangling over wording. For example, North's sole contribution to the statement reads:

"In addition, human-induced climate change may alter atmospheric circulation, dislocating historical patterns of natural variability and storminess." 

"Talk about a storm," he said. "They were all over me. The thing finally did prevail, but just a statement like that, if you have 12 or 13 people who know this or that or the other … it just goes on and on."

He noted that another statement on the counterintuitive effects of climate change on weather, such as cooling in some regions, has "a little bit" of an edge to it in anticipation that skeptics will point to such cooling as proof the planet isn't warming.

The statement notes that impacts from climate change will be myriad and harmful, ranging from extreme weather events to threats to agriculture and coastal infrastructure. 

"While important scientific uncertainties remain as to which particular impacts will be experienced where," the statement reads, "no uncertainties are known that could make the impacts of climate change inconsequential."

The statement is short on policy prescriptions to combat global climate change. North said policy is something that makes climate scientists as a group uncomfortable, but he added that adaptation will be key, given the political impasse on curbing emissions. 

"I think it is going to be very, very hard for the world to come to grips with this," he said. "So one thing we really need to do is think about adaptation: How are we going to adapt to climate change?"

John Roach is a contributing writer for NBC News. To learn more about him, visit his website