The first part of the 2013 report from the UN International Panel on Climate Change (IPCC) , and to no surprise has generated passionate reaction from all sides of the global warming issue.

As we recently reported, leaks of draft copies of the report said the panel was backing off some warming predictions in small but significant ways, in part in reaction to the pause in global warming trends over the past 15 years or so that has gone against the predictions of many warming models.

The level of "carbon sensitivity" – how much temperatures are impacted by a given level of increase in carbon in the atmosphere – was also said to have been scaled back a bit.

Many reports said such language in the draft report was criticized fiercely by dozens of IPCC reviewers, and the IPCC itself said in effect to "not place to much emphasis on a draft version." (See New UN Climate Report Said to Dial Back Global Warming Predictions.)

This is the fifth such UN report, and the first since 2007. It is also the first since negotiations for a global treaty reining in carbon emissions collapsed in Copenhagen in 2009; the first since questions were raised about the integrity of the IPCC itself following mistaken claims about the speed of glacier melt in the Himalayas and the first since evidence became accepted that global surface air temperatures have risen much less quickly in the past 15 years than the IPCC had expected.

To be honest, even the 36-page summary report for policy makers is very difficult to get through, let alone the full report, but we will provide a summary here of key findings.

The bottom line: the IPCC is more certain now than before that temperatures are rising and that man-made forces are responsible for a significant share of those increases. That said, the IPCC did scale back predictions for future temperature increases marginally.

Here are some of the highlights:

• Average global temperatures across both land and oceans have risen about .85 degrees Celsius from 1880 to 2012. That said, there is always quite a lot of variability in such temperatures year to year and over periods of time, the report notes.

• "It is virtually certain" that global temperatures have risen since the mid-20th century. As the graphic below shows (based on IPCC data – not all agree), averages temperatures have risen about .5 degree C since 1950.

UN Data Shows Continuous If Still Modest Rise in Global Temperatures Since 1950

• The number of extreme weather events (such as record cold and hot days) has increased since the 1950S, but the level of confidencd is either likely or very likely, depending on the type of event.

• While it is very likely that Artic sea ice has been decreasing since 1979, Antarctic ice has been increasing over the same period, though at a lower rate.

• It is very likely that sea levels have risen about 3.2 millimeters per year since between 1993 and 2010.

• Atmospheric concentrations of the greenhouse gases carbon dioxide and methane have increased 40% and 150% since 1750.

• Average greenhouse gas emissions in the 2002-2011 period were 54% greater than in 1990. [SCDIgest note: that rate of increase in such a short period of time has to be largely connected to the rise of China over the period. China is the world's largest emitter of greenhouse gases.]

• It is "extremely likely" (probability of over 95%) that man is responsible for about 50% of the warming. In 1995, the second report merely suggested a link between rising temperatures and human activity. In 2001, the connection was deemed "likely" (66% chance) in 2001, "very likely" (90%) in 2007.

For the first time, the IPCC gives some credence to the possibility that Earth's climate may not be responding to higher concentrations of greenhouse gases quite as sharply as was once thought. The response is referred to as "equilibrium climate sensitivity," defined as the rise in surface temperatures in the long term which accompanies a doubling of the concentration of CO2 in the atmosphere. In its previous report, the IPCC put impact at between 2 -4.5 degrees C, with a most likely figure of +3 degrees. Now it says that sensitivity might be somewhat lower, in the 1.5-4.5 degrees C range, driving down it would follow the "most likely" number, though one is not provided in the 2013 report.

The IPCC has set what is sometimes called a carbon budget. To have a two-thirds chance of keeping global warming below 2 degrees C "will require cumulative CO2 emissions from all man-made sources to stay between below 1,000 trillion metric tons. Unfortunately, the world had already blown through just over half that amount (531 trillion tons) by 2011. At current rates of GHG emissions, the rest of the budget will have been spent before 2040. A 2-degree rise is often viewed as a level above which will cause real environmental problems.

The IPCC did address the pause in warming trends since 1998, saying that "The rate of warming over the past 15 years was 0.05 degree C per decade...smaller than the rate calculated since 1951." In its 2007 report the IPCC had said the rate of warming was 0.2 degree C per decade in 1990-2005 (four times the current rate). It then predicted that this would continue for the next two decades.

The explanation? The report says that "due to natural variability, trends based on short records are very sensitive to the beginning and end dates and do not in general reflect long-term climate trends." It also says the heat may be ominously building in the "deep oceans," though there is little data to support that yet.

The report was hailed by many climatologists and others, saying it was a new call to urgent action to reduce carbon and other emissions.

Others were not as sure.

A Wall Street Journal editorial said that "Temperatures have been flat for 15 years, nobody can properly explain it (though there are some theories), and the IPCC doesn't want to spend much time doing so because it is politically inconvenient and shows that the computer models on which all climate-change predictions depend remain unreliable."

The WSJ added that "One lesson of the IPCC report is that now is the time for policy caution. Let's see if the non-warming trend continues, in which case the climate models will need remodeling. But that's far less costly than trying to undo grand global redistribution schemes like carbon cap and trade."

Conversely, IPCC co-chairman Thomas Stocker calls climate change "the greatest challenge of our times," and once again calls for immediate and substantial action.

It's not easy reading, but if anyone wants to see the IPCC reports, they can be found here.

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