The IPCC authors note it is "virtually certain"—a 99-100 percent probability—that daily temperatures will continue to rise worldwide throughout the 21st century. Heat waves will increase in length, frequency and intensity. Extreme hot days that happened once every 20 years will now happen once every two years. These record-breaking warm periods could be as much as 5.4 degrees Fahrenheit higher by 2050 than they are today, and as much as 9 degrees Fahrenheit higher by the late end of the century. The higher temperatures could alter landscapes and put enormous pressure on people's livelihoods.
Droughts: Droughts, along with all the problems they cause, including food and water shortages and resulting conflicts over the scarce resources, will continue to intensify in the 21st century. Regions of southern and central Europe, the Mediterranean, southern Africa and parts of North, Central and South America will be the hardest hit, due to "reduced precipitation" in those areas and more evaporation, which dries up bodies of water and soils.
Storms: Hurricanes are powered by the release of moisture and heat from warm oceans. So, naturally, as sea temperatures rise due to greenhouse gas increases, these storms are expected to become stronger—though not necessarily more frequent.
Warmer temperatures can trigger a shift toward weak El Nino-like conditions, which reduce hurricane activity. The ones that do form, however, will be much more intense, with higher wind speeds and more rain, the IPCC said, as increasing sea temperatures fuel the intensity of the cyclones. Hurricanes and other storms will also continue to shift poleward, exposing areas that historically have only rarely seen the effects of hurricanes, like northern New England states, to more damage. Heavy precipitation in the form of snow and rain will increase in some areas, particularly in the tropics and in high latitudes. Massive downpours that happened only once every 20 years could happen once every five years, the IPCC said, contributing to more frequent flooding and landslides.
The scientists said they are unable to predict what will happen to small-scale storms like tornadoes, due to limitations in today's climate models to forecast them and to conflicting predictions in the literature. Some researchers say climate changes could limit tornadoes; others say they would fuel them.
The IPCC boasts 194 member countries and 2,000-plus contributing scientists and reviewers. Who contributed to this particular report, and how did it come about?
The idea for a special report on extreme weather was first proposed in 2008 by Norway and the International Strategy for Disaster Reduction, a UN agency, which appealed to the IPCC to lay out comprehensive steps for managing the risks of climate-driven extremes. The science panel was coming off a seminal year. Its 2007 assessment concluded for the first time that the Earth is warming and that human activities are "very likely" to blame. At the end of that year it shared the Nobel Peace Prize with Vice President Al Gore.
By 2009, the panel had organized a collaboration to research and write SREX between IPCC working groups I and II, which focus on the science behind climate change and on vulnerability and adaptation, respectively. Co-chairs of the groups—Qin Dahe of the Chinese Meteorological Administration, Thomas Stocker of the University of Bern in Switzerland, Vicente Barros of the University of Buenos Aires and Christopher Field of the Carnegie Institution of Science at Stanford—directed a group of 80 authors, 19 reviewers and more than 100 contributing authors, the IPCC said.
In total, 220 authors from 62 countries participated in the report, which included nearly 19,000 review comments.
Why does the IPCC address some of its findings in generalities? Where are the hard figures and pages of data?
The IPCC has so far only released a 29-page summary of SREX's "key findings" for the world's policymakers, which it releases with all of its reports. The summary was approved by all 194 governments and was the product of political negotiations.
The full report will be released in February 2012.
Does SREX really change our understanding of how climate change affects extremes?
Not really. Scientists have been piecing together the connection between human-caused climate change and weather extremes for years. But this is the first attempt to condense all the findings into a single comprehensive report, while also exploring the broader implications on communities and economies.
However, given that it took a few years to put together, Gavin Schmidt, a climatologist at the NASA Goddard Institute for Space Studies and contributor to previous IPCC reports, cautioned that the report may already be obsolete by the time all the data is published in February. "It will not be up to date with the latest thinking on [extremes], which is pretty fast moving. And the document certainly isn't going to blaze some new path forward," Schmidt said in an email.