This article describes two greenhouse gas (GHG) emission scenarios covering the period 1990–2100. The first of these, the B2 scenario, is a successful attempt to provide an internally consistent quantification—checked by the computer models Scenario Generator (SG), MESSAGE, MACRO, and MAGICC—of key variables describing a plausible but unremarkable “storyline” that complements the other storylines discussed in this special issue of Technological Forecasting and Social Change. In the B2 scenario global carbon emissions from energy use and industrial sources rise from 6.5 gigatons of carbon (GtC) in 1990 to 14.2 GtC in 2100. Primary energy use climbs from 350 exajoules (EJ) to 1360 EJ. The global primary energy structure shifts away from gas and oil (28% in 2100 compared to 55% in 1990) and toward non-fossil energy sources (50% in 2100 compared in 18% in 1990). The share of coal is 22% in 2100, only four percentage points lower than in 1990. Among regions there are significant variations in the primary energy structure. Synthetic liquid fuel production grows to 330 EJ in 2100, driven largely by assumptions about the long-term decline of oil and a continuation in current trends towards increasingly flexible, convenient, and cleaner forms of final energy. On the global level sulfur emissions decline from 63 megatons of sulfur (MtS) in 1990 to 43 MtS in 2100. Radiative forcing grows by approximately 1% per year from 1990 through 2100. The “best guess” temperature change (assumed climate sensitivity = 2.5°C) associated with this increase in radiative forcing is 2°C in 2100. The B2S550 scenario is a variation of the B2 scenario constrained to stabilize the atmospheric carbon concentration below 550 parts per million by volume (ppmv). Carbon emissions in the B2S550 scenario peak in 2040 at 10.7 GtC, before dropping to 5.5 GtC by 2100. Roughly 40% of the 8.7 GtC difference in 2100 between the B2 scenario and the B2S550 scenario is due to fuel switching, primarily away from coal. 32% is from carbon scrubbing, 14% is due to price-induced energy demand reductions, and 12% is from hydrogen injection into the natural gas system. The B2S550 scenario's radiative forcing in 2100 is 8% lower than that of the B2 scenario, and its best guess temperature change is 0.2°C lower.