National Climate Assessment, 2014, United States Group: A Key Graph and Explanation from that Report

NCA-2014-graph temp change to 2099_average-annual-temp_global_V6_1

Figure 2.4: Different amounts of heat-trapping gases released into the atmosphere by human activities produce different projected increases in Earth’s temperature. In the figure, each line represents a central estimate of global average temperature rise (relative to the 1901-1960 average) for a specific emissions pathway. Shading indicates the range (5th to 95th percentile) of results from a suite of climate models. Projections in 2099 for additional emissions pathways are indicated by the bars to the right of each panel. In all cases, temperatures are expected to rise, although the difference between lower and higher emissions pathways is substantial. (Left) The panel shows the two main scenarios (SRES – Special Report on Emissions Scenarios) used in this report: A2 assumes continued increases in emissions throughout this century, and B1 assumes much slower increases in emissions beginning now and significant emissions reductions beginning around 2050, though not due explicitly to climate change policies. (Right) The panel shows newer analyses, which are results from the most recent generation of climate models (CMIP5) using the most recent emissions pathways (RCPs – Representative Concentration Pathways). Some of these new projections explicitly consider climate policies that would result in emissions reductions, which the SRES set did not., The newest set includes both lower and higher pathways than did the previous set. The lowest emissions pathway shown here, RCP 2.6, assumes immediate and rapid reductions in emissions and would result in about 2.5°F of warming in this century. The highest pathway, RCP 8.5, roughly similar to a continuation of the current path of global emissions increases, is projected to lead to more than 8°F (4.4°C) warming by 2100, with a high-end possibility of more than 11°F (6°C) . (Data from CMIP3, CMIP5, and NOAA NCDC).

(note to help with graph above: if you are not familiar with changing Fahrenheit to Centigrade in the sense used here — changing a given number of degrees from one to the other, not a specific reading on the thermometer of one to the other, just use this: For F to C multiply the F by .5555. For C to F, multiply C by 1.8. Thus 2°C = 2 x 1.8 = 3.6F)

The report from which this graph was taken was created by a team of more than 300 experts guided by a 60-member Federal Advisory Committee which was extensively reviewed by the public and experts, including federal agencies and a panel of the National Academy of Sciences. The Report is called the 2014 National Climate Assessment and summarizes the impacts of climate change on the United States, now and in the future..  See a full summary of that report here and the actual report here. 

Another Graph from this Report is below:

National Climage Assessment-CS_global_temp_projections_V7

Figure 2.5: Projected change in average annual temperature over the period 2071-2099 (compared to the period 1970-1999) under a low scenario that assumes rapid reductions in emissions and concentrations of heat-trapping gases (RCP 2.6), and a higher scenario that assumes continued increases in emissions (RCP 8.5). (Figure source: NOAA NCDC / CICS-NC).