It is estimated that US energy-related CO2 emissions in 2001 totalled 5,692 Mt. To put US emissions in a global perspective, total energy-related CO2 emissions for the world in 2001were estimated at 23,899 Mt, making US emissions about 24% of the world total. Emissions for the industrialised world, that is, North America, Western Europe, and industrialised Asia, in 2001 are estimated at 11,634 Mt, or about 49% of the world total, implying that US emissions represent about 49% of the energy-related CO2 emissions from the industrialised world. The remaining 51% of 2001 worldwide energy-related CO2 emissions come from developing countries with 9,118 Mt and the former Soviet Union and Eastern Europe with 3,148 Mt. By 2025, however, the US share of total world emissions is projected to fall to 22% or 8,142 Mt out of a global total of 37,124 Mt. The reason for the expected decline in the US share is that energy-related CO2 emissions from the developing countries are projected to increase at an annual rate of 2.7%, while emissions from the industrialised countries increase by 1.2% annually.
From an economic perspective, US GDP in 2001 was USD 9,394 bn (in constant 1997 USD), compared with an estimated global total GDP of USD 32,354 bn. Thus, the US share of world economic output in 2001 was about 29%. In 2025, when the world’s total GDP is projected to be USD 65,574 bn, US share is projected to be USD 18,881 bn, or still about 29%. In other words, the US is projected to maintain its share of economic output while its share of global emissions shrinks.
Although power generators in the US have decreased their emissions of these substances since the enactment of the CAAA, fossil fuel combustion still contributes a significant proportion of the total SO2, NOx and mercury released into the atmosphere. According to the US EPA, emissions from burning fossil fuels for power generation continue to result in serious health and environmental impacts.
Existing regulations will require substantial additional reductions in SO2 and NOx emissions, and pending regulations will limit mercury emissions. However, new multi-pollutant regulatory initiatives, including two bills introduced in Congress and the Clear Skies Initiative, could replace some of these existing requirements and may include regulation of CO2 as well.