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By John Roach
This file photo shows 2012 flooding in Wales, one of the wettest in Britain on record. A report issued today from the Intergovernmental Panel on Climate Change says scientists are 95 percent certain that humans are thePaul Ellis / AFP - Getty Images

Politicians and activists seized on a major scientific report saying that human activity is "extremely likely" to be the dominant cause of global warming — and used it to prod world leaders toward a global deal to curb greenhouse-gas emissions.

"The future we are heading to is not the future we want to leave to our children and grandchildren and future generations," Alden Meyer, director of strategy and policy for the Union of Concerned Scientists in Washington, told NBC News. 

"It is not that we don't understand the problem. It is not that we don't understand that we're heading towards a future with extremely dangerous impacts. And it's not that we're not aware that we have the technology solutions," he said. "It is a failure in our political process and our policy process."

He added that "cost-effective solutions (are) more plentiful than ever" — solutions such as solar and wind power as well as greater energy efficiency.

Policy choices
Friday's report is the fifth assessment from the Intergovernmental Panel on Climate Change issued since 1990. The reports are not intended to direct policy, but to inform policymakers by describing the amount of climate change observed and what the climate models say about the future under various scenarios of greenhouse-gas emissions. 

The 20-year-plus existence of the climate panel now provides a test for the models' ability to predict changes in temperature, sea level and concentrations of greenhouse gases — and thus provides "greater evidence for confidence in the models," Linda Mearns, a climate scientist with the National Center for Atmospheric Research and a report review editor and contributing author, told reporters in a press call Friday.

This increasing confidence, in turn, gives the scientists more faith in the ability of models to paint a picture of the future so that policymakers can understand their choices, Gerald Meehl, a climate scientist with the National Center for Atmospheric Research and lead author of the report's chapter on near term projections, said during the call.

"One positive message that comes out of this report is that we do have a choice," he said. "What the science has demonstrated is here are four possible futures with four levels of climate change. We can choose to actively mitigate, to cut emissions, and we'll end up on one of those lower pathways. If we don't really do much of anything, we'll end on the higher one."

A key point raised in the report is that, to keep warming below an internationally agreed target of 3.6 degrees Fahrenheit (2 degrees Celsius), nearly 80 percent of the world's projected fossil fuel reserves need to remain underground, noted the activist group, which is leading a campaign to encourage colleges and universities to divest from their investments in oil and coal companies.

"We know beyond any doubt that carbon is warming the atmosphere," co-founder Bill McKibben, a writer and environmentalist, said in a statement. "But we also know beyond any doubt that fossil-fuel money is polluting the politics of climate. That's why we keep building movements."

Skeptics losing ground
Politicians and activists who are skeptical of the alarm over global climate change continued to press their cause as well. U.S. Sen. James Inhofe, R-Okla., said in a statement that the latest report "proves that the U.N. is more interested in advancing a political agenda than scientific integrity."

"The IPCC glossed over the ongoing 15-year pause in temperature increases and did nothing to suggest that their predictions might be wrong," Inhofe said. "With climate change regulations expecting to cost the U.S. economy millions of jobs and between $300 billion and $400 billion in lost GDP a year, we can't afford to act on politically charged media alarmism."

On Thursday, Inhofe filed amendments to Congress' continuing resolution that would bar the Environmental Protection Agency from regulating greenhouse-gas emissions from power plants, and would prohibit the federal government from participating in international climate talks unless it issued a statement saying that human-caused climate change is a "scientifically unproven theory."

The Heartland Institute, a libertarian think tank, released a statement saying that the authors of its own panel report "do not believe man-made global warming is a crisis, or that scientists know enough about how the climate works to make policy-relevant recommendations to the world's government leaders."

Pushback to such claims, however, is strong. Secretary of State John Kerry said in a statement, "This isn’t a run-of-the-mill report to be dumped in a filing cabinet. This isn’t a political document produced by politicians. It’s science."

He added, "It builds on the most authoritative assessments of knowledge on climate change produced by scientists, who by profession are conservative because they must deal in what is observable, provable and reviewable by their peers."

What's more, noted the World Resources Institute, the IPCC's findings are reinforced by "many other leading authorities" including the National Academy of Sciences, Global Change Research Program, National Oceanic and Atmospheric Administration, and UK Met Office. "Future generations are depending on us to wake up to this global challenge," the World Resources Institute said in a statement. "It is time for our leaders to answer the call."

Last of its kind?
Friday's report was actually just a 36-page executive summary of a 14-chapter assessment of climate science, which is due for release on Monday. Three more IPCC reports are to be published over the next year, focusing on climate impacts, potential ways to mitigate those impacts, and the overall climate picture.

The next round of international climate negotiations is due to take place in Warsaw in November — with follow-up meetings scheduled in Lima in 2014 and Paris in 2015. Paris provides the likeliest opportunity for a new global pact on greenhouse-gas limits.

In an editorial, the journal Nature said the IPCC's current "mega-assessment" should be the last of its kind. Nature's editors said climate scientists should focus instead on "smaller and more rapid assessments of more pressing questions that have a particular political interest and for which the science is evolving quickly."

"Such a structure might also help to avoid an unfortunate consequence of the current framework, which ensures that the IPCC's mega-assessments are out of date by the time they hit the streets," the editors said.

John Roach is a contributing writer for NBC News. To learn more about him, visit his website. NBC News' Alan Boyle also contributed to this report.