“IPCC 2013, Similar Forecasts, Better Certainty”


The summary for the new Intergovernmental Panel on Climate Change (IPCC) report can be read here (pdf). Richard Schiffman asked various experts for a headline that captures the new report:

Ted Scambos, a glaciologist and head scientist of the National Snow and Ice Data Center (NSIDC) based in Boulder would lead with: “IPCC 2013, Similar Forecasts, Better Certainty.” While the report, which is issued every six to seven years, offers no radically new or alarming news, Scambos told me, it puts an exclamation point on what we already know, and refines our evolving understanding of global warming. …

It is now 95 percent likely that human spewed heat-trapping gases — rather than natural variability — are the main cause of climate change, according to today’s report. In 2007 the IPCC’s confidence level was 90 percent, and in 2001 it was 66 percent, and just over 50 percent in 1995.

Eric Holtaus explains why the IPCC report is significant:

What makes the IPCC so important is simple: They are required to agree. Last night, the group pulled an all-nighter to ensure that representatives from all 195 member countries agreed on every single word of the 36-page “summary for policymakers” (pdf). That instantly makes the report the world’s scientific and political authority on what is happening to the climate, what will happen in the future, and what needs to be done to avoid the worst impacts.

Chris Mooney digs into the report’s details:

The IPCC has added considerable clarification to the most controversial part of the report, where it notes that the rate of surface temperature increase over the last 15 years ago is somewhat less than it had been previously. After an earlier draft of the report leaked in August, this section was widely cited by climate skeptics to cast doubt on global warming. Now, the IPCC clarifies that short-term trends of this kind “are very sensitive to the beginning and end dates and do not in general reflect long-term climate trends.” The report says the recent reduction in the rate of warming is caused, in roughly equal parts, by natural climate variability (possibly including heat going deeper into the oceans) and a temporary decline of solar radiation reaching the planet, thanks to volcanic eruptions and the solar cycle itself.

Scott K. Johnson examines the emissions estimates:

In order to keep warming below the oft-referenced target of 2°C above pre-industrial temperatures, the total amount of carbon humans have emitted cannot exceed about 800 gigatons, the report says. As of 2011, about 531 gigatons had been emitted. The two middle scenarios involve the emission of 595-1250 gigatons between now and the end of the century.

The report also emphasizes the need to consider the long-term ramifications of carbon dioxide emissions. “Depending on the scenario, about 15 to 40 percent of emitted CO2 will remain in the atmosphere longer than 1,000 years.”

Brad Plumer, meanwhile, thinks it’s time the IPCC begins rethinking its mission:

[M]any experts have begun urging the IPCC to rethink its whole mission. Do we really need hundreds and thousands of scientists devoting years of their lives to an encyclopedic synthesis that is getting a bit repetitive? Would it be more useful for the IPCC to produce more frequent, nimble reports on important sub-topics, as it did in 2012 when it released a smaller “special report” on extreme weather?

It’s a topic the IPCC has even begun asking itself.