A lake formed from melt water from the Pastoruri glacier, as seen from atop the glacier in Huaraz, September 19, 2013. The nearby Pastoruri glacier is one of the fastest-receding glaciers in the Cordillera Blanca mountain range, according to a 2012 paper by the University of Texas and the Huascaran National Park. (Reuters/Mariana Bazo)

One of the most comprehensive scientific reviews ever assembled confirms what most people already acknowledge about climate change: it is happening, human activity is causing it, and we have a rapidly closing window of time to prevent unprecedented, potentially catastrophic climatic shifts.

What the Intergovernmental Panel of Climate Change report summary released this morning in Stockholm adds is near-certainty that warming is man-made, and stronger language to describe the changes underway.

Global warming is “unequivocal,” and its effects “unprecedented over decades to millennia,” states the IPCC, which considered the research of some 600 scientists from thirty-two countries, and concluded that there are more greenhouse gases in the atmosphere now than at any point in at least 800,000 years. “It is extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century,” states the report. Fossil fuel emissions and to a lesser extent land-use changes account for a 40 percent increase in carbon dioxide concentrations since pre-industrial times.

According to the IPCC, the atmosphere can absorb no more than 1 trillion tons of carbon dioxide without warming exceeding 2 degrees Celsius, the threshold scientists have agreed is crucial to stay below in order to prevent the most catastrophic effects of climate change. More than half of that carbon dioxide has already been emitted, and the world is on track to pump out the rest within 40 years, The New York Times reports. (Other models suggest we have even less time.)

Climate change is not only unprecedented but also “irreversible on a multi-century to millennial time scale.” Even if no new greenhouse gasses were added to the atmosphere, temperatures will stay high for centuries. And don’t count on geoengineering to save the planet. Proposed solutions like sucking carbon out of the atmosphere or spraying sulfur into the air to block sunlight face “biogeochemical and technological limitations,” and, in the case of solar radiation management, would “modify the global water cycle, and would not reduce ocean acidification.”

The report is the strongest show yet of the scientific consensus on the occurrence and implications of anthropogenic climate change, but it is unlikely to stir up any political action in proportion to the science. “This is science, these are facts, and action is our only option,” Secretary of State John Kerry said in a statement in response to the report. The report’s near-certainty in linking human activity to climate change is striking in light of the fact that the 1990 report did not quantify the human contribution at all, and the 1995 report pointed only to a “discernable human influence on climate.”

But the right has not been waiting for better science in order to make up its mind about climate change. Conservatives long ago decided that “science” was a liberal scheme, in order to disregard its policy implications. Efforts to implement reproductive health restrictions around the country that directly contradict medical knowledge testify to this end. The media’s obsession with “balance” also dulls the influence of scientific consensus, by granting unsubstantiated denials the same weight as evidence-backed experts.

“The IPCC glossed over the ongoing fifteen-year pause in temperature increases and did nothing to suggest that their predictions might be wrong,” said Oklahoma Senator Jim Inhofe, a Republican member of the Environment and Public Works Committee. In fact, the report’s authors went to some length to consider the perceived slowdown in temperature rise, concluding that the oceans have absorbed more heat than normal in recent years, and that short-term patterns “do not in general reflect long-term climate trends.” Variance in the levels of certainty for specific projections are made clear throughout the report. The true uncertainty in climate science is how a global shift will play out locally and regionally. It’s difficult to model, particularly since the changes are “unprecedented,” and that is precisely what makes it so dangerous to carry on business as usual.

At this point even the things we can predict, like the number of years we have until we cross the emissions threshold, are of limited use. Knowing how much carbon the world can emit helps governments set reduction targets, but these targets don’t mean much if we can’t design and implement policies to help us meet them. That means not only “saying no” to projects that perpetuate dependency on fossil fuels, like Keystone XL, but incubating creative alternatives in both the technological and political realm.

For conservatives, as David Roberts explains, accepting climate science means acknowledging the gravity and urgency of global warming, which would force into public the choice between sweeping new federal policies or massive human suffering. That climate denial is in effect choosing the latter is what needs to be made clear to the public.

Republican lawmakers like Lamar Smith have already discredited the report for being “more political than scientific,” and though he’s wrong about the rigor of the IPCC’s review, it will be more productive for progressives to challenge the climate deniers’ politics, rather than their science. It is the same politics of greed and cruelty displayed in the vote to cut food stamps, in the opposition to healthcare reform, and in the disregard for the wellbeing of workers and immigrants. Of course congressional Republicans aren’t the only stumbling block to climate progress, just as they aren’t the sole cause of economic inequality. But if predatory capitalism is the enemy, not just emissions, the coalition of allies is much, much larger.

Omar Ghabra on the loss of his homeland, Syria.