NewsJanuary 14, 2013

5 Must-See Charts From Major New U.S. Climate Report

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Andrew Freedman

By Andrew Freedman

A major new federal climate science assessment, released in draft form on Jan. 11, finds that “climate change is real and accelerating,” and that myriad impacts are already being felt in the U.S., from more frequent, hotter heat waves, to coastal flooding and precipitation extremes. The report, which is the first since 2009 to systematically examine the effects of global warming on the U.S., bolsters some of the conclusions of the previous report and cites new findings showing that the country is already experiencing a wide range of disruptive impacts from global warming, primarily through the changing frequency and severity of weather extremes.

For example, the report cites “strong evidence” that manmade global warming has “roughly doubled” the probability of extreme heat events, such as the record hot summer of 2011 in Oklahoma and Texas. It also notes that sea level rise is exacerbating storm surge problems along the East and Gulf Coasts, and that sea level rise played a role in exercerbating the impacts of Hurricane Sandy.

Global annual average temperature (as measured over both land and oceans; scale on left) has increased by more than 1.4°F (0.8°C) since 1880. Red bars show temperatures above the long-term average, and blue bars indicate temperatures below the long-term average. The black line shows atmospheric carbon dioxide (CO2 concentration in parts per million (ppm); scale on right. While there is a clear long-term global warming trend, some years do not show a temperature increase relative to the previous year, and some years show greater changes than others. These year-to-year fluctuations in temperature are due to natural processes, such as the effects of El Niños, La Niñas, and the eruption of 12 large  volcanoes. Figure source: NOAA NCDC. Temperature data from NOAA NCDC 2012; CO2 data from NOAA ESRL 2012.
Click to enlarge the image. Credit: National Climate Assessment.

Many news outlets have already provided broad summaries of the draft assessment, including the The GuardianWashington Post, Los Angeles Times, Nature, and the Huffington Post. (The executive summary from the report itself is posted below.) But digging deeper through the nearly 1,200-page report reveals there are myriad charts that update past findings on climate change, and which take advantage of recent advances in computer modeling to provide new insights as well.

First and foremost, the report strongly states that human activities — mainly the burning of fossil fuels for energy, which emits heat-trapping greenhouse gases — are changing the climate in ways that are already harming the U.S.

“Climate change is already affecting the American people,” the report said, citing extreme weather events, rising and acidifying seas, in particular. “These changes are part of the pattern of global climate change, which is primarily driven by human activity.” 

The colors on the map show temperature changes over the past 20 years in °F (1991-2011) compared to the 1901-1960 average. The bars on the graphs show the average temperature changes by decade for 1901-2011 (relative to the 1901-1960 average) for each region. The far right bar in each graph (2000s decade) includes 2011. The period from 2001 to 2011 was warmer than any previous decade in every region. (Figure source: NOAA NCDC / CICS-NC. Data 11 from NOAA NCDC. )
Click to enlarge the image. Credit: National Climate Assessment.

The report said that the U.S. has already warmed by 1.5°F on average since 1895, with more than 80 percent of that increase occurring since 1980, and it projects a further warming of up to 4°F during the next few decades. Depending on how successful the global community is at slashing emissions of greenhouse gases—with little success so far—the report projects the U.S. will warm between 3°F to as much as 10°F by the end of the century. According to the report, the world is currently on a path to exceed the highest emissions scenario put forward by the U.N. Intergovernmental Panel on Climate Change (IPCC), which is an indication that the highest-warming scenario may be the most plausible one at this time.

The largest uncertainty in projecting future climate change is the level of emissions. The most recent model projections (shown above) take into account a wider range of options with regard to human behavior; these include a lower emissions scenario (RCP 2.6, top left) than has been considered before. This scenario assumes rapid reductions in emissions – more than 70 percent cuts from current levels by 2050 – and the corresponding smaller amount of warming. On the high end, they include a scenario that assumes continued increases in emissions (RCP 8.5, bottom right) and the corresponding greater amount of warming. Also shown are temperature changes (°F) for the intermediate scenarios RCP 4.5 (top right, which is most similar to B1) and RCP 6.0 (bottom left, which 4 is most similar to A1B; see the Appendix). Projections show change in average surface air temperature in the later part of this century (2071-2099) relative to the late part of the last century (1971-2000). (Figure source: NOAA NCDC / CICS- 7 NC. Data from CMIP5.)
Click to enlarge the image. Credit: National Climate Assessment.

A key point regarding future warming is that much depends on choices made during the next one to two decades, and how sensitive the climate system is to the continued buildup of greenhouse gases. “There is mounting evidence that the costs to the nation [of global warming] are already high and will increase very substantially in the future, unless global emissions of heat-trapping gases are strongly reduced,” the report said.

The colors on the map show annual total precipitation changes (percent) for 1991-2011 compared to the 1901-1960 average, and show wetter conditions in most areas (McRoberts and Nielsen-Gammon 2011). The bars on the graphs show average precipitation differences by decade for 1901-2011 (relative to the 1901-1960 average) for each region. The far right bar is for 2001-2011. (Figure source: NOAA NCDC / CICS-NC. Data from NOAA NCDC.)
Click to enlarge the image. Credit: National Climate Assessment.

The report details precipitation changes across the U.S., and shows that while many regions are getting wetter in response to the warming climate, other areas are drying. In particular, the report shows that the Southwest, Southeast, and the Rocky Mountain states have seen precipitation decreases. These trends are exacerbating water supply concerns and increasing drought and wildfire risks as well. 

The report is the product of more than 240 experts from multiple agencies and scientific institutions. It is now subject to public comment, and will undergo a review by the National Academy of Sciences, National Oceanic and Atmospheric Administration (NOAA), and other government agencies, before being transmitted to the White House and Congress. The report draws from studies published through July 31, 2012, although it also includes references to extreme events that happened after that date, such as Hurricane Sandy, which occurred in late October.

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