Final answer:
The IPCC AR4 carbon emission scenario, also known as the Special Report on Emissions Scenarios (SRES), includes the B1, A1B, and A2 scenarios depicting low, medium-high, and high future emissions and their effect on global temperatures relative to pre-industrial levels.
Step-by-step explanation:
The IPCC AR4 carbon emission scenario, commonly referred to as the Special Report on Emissions Scenarios (SRES), provides a range of potential future emissions of greenhouse gases based on different assumptions about population growth, economic development, and technological progression. The three outlined scenarios are B1 (low emissions scenario), A1B (medium-high emissions scenario), and A2 (high emissions scenario), which depict various projected changes in global average temperatures when compared to the 1961-1990 averages.
The B1 scenario envisions a world with rapid economic changes, an emphasis on environmental sustainability and equity, and a global population that starts to decline midway through the 21st century. The A1B scenario depicts a future with rapid economic growth, global population peaking in mid-century, and balanced use of all energy sources. The A2 scenario assumes a more heterogeneous world with self-reliance and preservation of local identities, higher population growth, and less concern for rapid economic development.
These scenarios are critical in understanding potential climate change impacts and formulating climate policies. They take into account the radiative forcing associated with different concentrations of CO₂ and other greenhouse gases in the atmosphere, and the subsequent estimated rises in Earth's average surface temperature.