Published today, “Climate Change 2013: The Physical Basis” is the first of a series of reports that will be finalized and released by the Intergovernmental Panel on Climate Change (IPCC) over the next 12 months, and this is the one that will garner the most attention.

Officially known as the Working Group I Contribution to the Fifth Assessment Report, each assessment comes along roughly every six years (the last was in 2007), and each volume of each assessment contains many hundreds of pages of distilled research — compiling the evidence of how much the climate is changing and modeling future climate change scenarios.

Wait? It’s Released Today? So Why All the Coverage on Friday?

Fortunately for those of us who aren’t climate scientists or who don’t have the wherewithal to read through hundreds upon hundreds of pages, each Working Group report comes with a “Summary for Policymakers,” which is significantly shorter (at approximately 30 pages) and focuses on the bare essentials of the larger report. It was the summary report that was released on Friday and which spawned so much media coverage.

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Who or What Is the IPCC?

The IPCC, or Intergovernmental Panel on Climate Change, was established in 1988 by the United Nations Environment Program (UNEP) and the World Meteorological Organization (WMO), “to provide the world with a clear scientific view on the current state of knowledge in climate change and its potential environmental and socio-economic impacts.” It has a relatively small secretariat, housed in WMO headquarters in Geneva, Switzerland. The IPCC itself does not conduct any research, not does it monitor climate-related data. What it does do is call upon the services and expertise of hundreds of scientists across the globe, who work to review and assess the most recent scientific, technical and socio-economic information produced worldwide related to climate science, and to produce these syntheses. The report published today has over 200 principal authors.

OK, So What Does the Report Say?

There are plenty of specifics, as is to be expected from a 2,000 page report. But generally speaking, Daryl Frears summed it up fairly succinctly in The Washington Post:

Some key findings were that the planet is warming at an accelerated pace without any doubt, that humans are causing it with 95 percent certainty and that the past three decades have been the hottest since 1850. Carbon concentrations in the atmosphere have increased 40 percent since then, and carbon, methane and nitrous oxide are at levels unprecedented in at least 800,000 years. Greenland and Antarctic ice sheets have steadily lost mass in two decades, and glaciers are shrinking worldwide. Sea-level rise could reach three feet by 2100.

In other words: yes, there is warming; the pace of the warming is increasing; the warming that is taking place is exerting noticeable effects; this warming is associated with extremely elevated levels of greenhouse gases; and humans are almost certainly responsible for it.

Does It Contain Anything New?

It depends what you mean by new. If you are a regular peruser of climate  science, then you likely are familiar with at least the broad parameters of what the report includes. What is exceptionally helpful, however, are the ways in which the IPCC synthesizes thousands of studies in an comparatively comprehensible way, allowing climate scientists to de facto speak as one voice. And IPCC material can be easily further condensed for amplification: witness, for example, this handy post from Climate Central, which takes five of the key graphics from the IPCC report to highlight the extent of the changes that have taken place and are potentially yet to come.

Furthermore, it is instructive to compare the conclusions of this assessment report with previous ones and see how increased evidence has led to increased certainty about both present-day climate change, but also its significance in the historical record. For example, in 2001, the IPCC noted that the last few decades were likely the warmest in the northern hemisphere for 1,000 years; six years later, that had been extended to 1,300 years; in the most recent report, it now stands at 1,400 years.

Additionally, the IPCC’s projections of sea-level rise are now higher than they were in 2007, there is an understanding than the Greenland ice sheet is less stable than was presumed six years ago, and projections of the earliest ice-free Arctic Ocean summers have been  moved forward from the end of the century to the middle of it.

And the IPCC feels able to make its statements with a greater degree of confidence as time goes on. For example, in 2007, it stated that ”Most of the observed increase in global average temperatures since the mid-20th century is very likely (90 percent confidence) due to the observed increase in anthropogenic greenhouse gas concentrations”; six years later, the relevant paragraph reads that, ”It is extremely likely (95 percent confidence) more than half of the observed increase in global average surface temperature from 1951 to 2010 was caused by the anthropogenic increase in greenhouse gas concentrations and other anthropogenic forcings together.” (Emphasis added.)

Wait. 95% Confident? So They’re Not Certain Then?

Non-scientists may look at that figure and think, “So there is some doubt,” especially if they’re inclined to be skeptical about anthropogenic climate change. Similarly, because scientists refer to climate change being caused by human activities as a theory (as they do, for that matter, evolution), to laypeople’s ears it can connote speculation rather than fact. But this is scientific terminology that means something entirely different to those who use it.

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By way of illustration, Seth Borenstein of the Associated Press asked a variety of scientists what 95 percent certainty about warming meant to them. He reported:

Top scientists from a variety of fields say they are about as certain that global warming is a real, man-made threat as they are that cigarettes kill. They are as sure about climate change as they are about the age of the universe. They say they are more certain about climate change than they are that vitamins make you healthy or that dioxin in Superfund sites is dangerous.

Earth is a complex system with a great deal of natural variation, and science is an inherently skeptical and self-correcting enterprise. But when it comes to climate change, the degree of uncertainty about the cause is very low. Continued Borenstein: “Climate change ‘is not as sure as if you drop a stone it will hit the Earth,’ Princeton University climate scientist Michael Oppenheimer said. ‘It’s not certain, but it’s close.’

What Does This Report Say About the Future?

Quite a lot, and it isn’t encouraging. The IPCC notes that, “Continued emissions of greenhouse gases will cause further warming and changes in all components of the climate system. Limiting climate change will require substantial and sustained reductions of greenhouse gas emissions.” For the first time, it quantifies a global ‘carbon budget,’ calculating that for global mean temperature increases to be held below 2 degrees Celsius (3.6°F), a level that has been described as a ‘prescription for disaster,’ total global carbon emissions would have to remain below 1,000 billion tons. Human activities have already released approximately half that amount. Additionally, it is also likely that more than 20 percent of emitted CO2 will remain in the atmosphere for more than 1,000 years, as a result of which a large part of anthropogenic climate change will be “irreversible on a human timescale” unless means are found to suck CO2 out of the atmosphere.

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When Does the IPCC Issue Its Next Report?

Working Group II, which assesses the vulnerabilities of socio-economic and natural systems to climate change, will meet and release its contribution to the Fifth Assessment in late March; Working Group III, which considers mitigation measures, will release its report in mid-April; and a synthesis report will be published next September.

IMAGE: Elevated view of the Norwegian Polar Institute’s research ship “RV Lance” in the Arctic sea ice near 82.5 degrees North during NPI’s ICE (“Ice, Climate, and Ecosystems”) scientific research expedition in the central polar basin during July – August 2012. The ship was attached securely to the floe of ice on the left side of the photograph, and the vessel moved with the floe as the ice floated freely in the Arctic Ocean, for the duration of various on-ice research activities. (Jenny E. Ross/Corbis)