The world’s top experts have spent years weighing all the evidence — here’s what you need to know about their findings.
The IPCC, or the Intergovernmental Panel on Climate Change, just released its latest scientific report that looks at what the world’s top experts understand about climate change. The review takes years to complete, and will be used for years as a vital resource for climate science.
During a briefing on the report Friday morning organized by The Climate Group, three of the lead authors offered blunt summaries of their work:
“Warming is unequivocal.” — Dennis Hartmann, one of the report’s coordinating lead authors, focusing on observations
“From all of these lines of evidence, we conclude that humans are the dominant cause of changes in the climate system.” — Nathaniel Bindoff, a coordinating lead author, focusing on attribution of climate change
“The oceans are still taking up heat,” even though warming has recently hit a speed bump at the surface — Jochem Marotzke a coordinating author, focusing on evaluating climate models
Beyond that, what does the average person need to know about what’s in the report?
- It’s happening and we’re doing it: This report concludes that the earth is unequivocally changing, and the evidence is clear that humans have a large role in how it has changed over the last 60 years.
- 95-100 percent certain: Each of the IPCC’s last five big reports found that climate science has gotten increasingly certain that the planet is warming, and humans are the main cause. Scientists have a 95-100 percent certainty (“extremely likely”) that humans are causing temperatures to rise. Directly from the report: “It is extremely likely that 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.” The report in 2001 was 66 percent certain, and the 2007 report was 90 percent certain. Scientific conclusions that cigarettes are deadly and that the universe is about 13.8 billion years old have similar levels of certainty.
- Warmest 30 years: The globe has already warmed 0.85°C from 1880 to 2012. 0.6°C of that warming happened since 1950, and “1983–2012 was likely the warmest 30-year period of the last 1400 years.”
- Pause? What pause?: The report itself does not mention the word “pause,” but does describe the long term and short term increase in temperature. Since 1880, the nine warmest years have happened since 1998. 1998 was a very warm year partially because a warm ocean caused by El Nino did not take up as much heat as normal, which made the atmosphere warmer. Without 1998′s anomaly, there is no “slowdown,” “plateau,” “pause,” or “speedbump.”
- Acidifying oceans: The lower the pH, the more acidic something is. The pH levels of the ocean surface dropped by 0.1 since the start of the industrial era, “corresponding to a 26% increase in hydrogen ion concentration.” There’s been that big of an increase with a change of 0.1 because the scale is logarithmic.
- Global pollution ceiling: For the first time, the world’s leading climate scientists officially called for an absolute upper limit on greenhouse gas emissions to limit warming. To have a 66 percent chance of limiting warming to 2°C, the world can’t emit more than 1,000 gigatons of carbon dioxide, total. Or 800 gigatons when accounting for methane emissions and land use changes. For context, by 2011, humans had already emitted 531 gigatons of CO2. Known fossil fuel reserves represent 2,795 gigatons, meaning burning more than 10 percent of them pushes the world over 2° of warming.
- Seas rising and warming:Oceans, shallow and deep, are where most of the increases in heat energy goes, “accounting for more than 90% of the energy accumulated between 1971 and 2010.” Sea level has risen 19 centimeters since 1901, and “The rate of sea level rise since the mid-19th century has been larger than the mean rate during the previous two millennia.”
- One of the most scrutinized documents on the planet: More than 2,000 scientists worked on this report, which has been reviewed by government, industry, and environmental groups. It is one of the most scrutinized documents on the planet.
- Massive amounts of data: The report’s authors analyzed “9,200 peer-reviewed studies, undergirded by a staggering two million gigabytes of numerical data,” according to Jeff Nesbit.
- Summary for policymakers: 110 nations joined the review process leading up to the release of the report, which is officially known as the “Fifth IPCC Working Group Report on the Physical Science Basis of Climate Change.” This report is a summary for policymakers, whereas the full report will be over 1,000 pages. The final 5th Assessment will be released in 2014, along with other reports on vulnerability and mitigation.
- ‘Yet another wakeup call’: Secretary of State John Kerry said of the report: “This is yet another wakeup call: Those who deny the science or choose excuses over action are playing with fire.” He concluded that, “the response must be all hands on deck. It’s not about one country making a demand of another. It’s the science itself, demanding action from all of us.”
- Most comprehensive ever: President Obama’s top science adviser, John Holdren, said the report “represents the most comprehensive and authoritative synthesis of scientific knowledge about global climate change ever generated.”
- Senators should pay attention: U.S. Senator Ed Markey, co-chair of the Bicameral Task Force on Climate Change, said “If Senators truly followed the science in this report, we’d have more than 95 votes for action to match the more than 95 percent certainty that we are altering our planet for the worse.”
- Deniers can’t pick a response: As Penn State’s Distinguished Professor of Meteorology Michael Mann points out, climate deniers haven’t settled on a specific narrative to attack the report. Some think the report shows a smaller threat and less certainty, some think the report is too mild to mention, while some think that consensus is a bad thing. Yet the report contains more certainty, contains a seriously unmild set of predictions, and after analyzing large streams of data, has a robust consensus on a complex issue.
- Blistering pace: To put the report’s findings in perspective, Stanford scientists Noah Diffenbaugh and Chris Field found that the current pace of warming is happening 10 times faster than any time over the last 65 million years.