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Thursday, March 18, 2010


John Blodgett
Specialist in Environmental Policy

Larry Parker
Specialist in Energy and Environmental Policy

In the context of climate change and possible responses to the risk associated with it, three variables strongly influence the levels and growth of greenhouse gas (GHG) emissions: population, income (measured as per capita gross domestic product [GDP]), and intensity of emissions (measured as tons of greenhouse gas emissions per million dollars of GDP). 

(Population) × (per capita GDP) × (Intensityghg) = Emissionsghg 

This is the relationship for a given point in time; over time, any effort to change emissions alters the exponential rates of change of these variables. This means that the rates of change of the three left-hand variables, measured in percentage of annual change, sum to the rate of change of the right-hand variable, emissions. 

For most countries, and for the world as a whole, population and per capita GDP are rising faster than intensity is declining, so emissions are rising. Globally, for the variables above over the period 1990-2005, the rates of change (Δ) in annual percent sum as follows (numbers do not add precisely because of rounding): 

Δ + per capita GDP Δ + Intensityghg Δ = Emissionsghg Δ 
(+1.4) + (+1.7) + ( -1.6) = (+1.6) 

As can be seen, global emissions have been rising at a rate of about 1.6% per year, driven by the growth of population and of economic activity. 

Within this generalization, countries vary widely. (Unless otherwise noted, comments about countries refer to the top-20 emitters as of 2005, who accounted for about 75% of world emissions that year.) Between 1990 and 2005, in some countries, including Brazil, Mexico, Indonesia, and South Africa, population growth alone exceeded the decline in intensity. For most countries, and for the world as a whole, per capita GDP growth exceeded the intensity improvement each achieved. Countries for whom intensity improvements were greater than their per capita GDP increases included Germany, the United Kingdom, the United States, France, and South Africa. And both the Russian Federation and the Ukraine, following their economic contractions in the 1990s, posted negative numbers for population, per capita income, intensity, and GHG emissions between 1990 and 2005. Besides the Russian Federation and the Ukraine, only the United Kingdom and Germany reduced their GHG emissions for the period (Germany being helped by reductions in the former East Germany). 

Stabilizing greenhouse gas emissions would mean the rate of change equals zero. Globally, with a population growth rate of 1.4% per year and an income growth rate of 1.7% per year, intensity would have to decline at a rate of -3.1% per year to hold emissions at the level of the year that rate of decline went into effect. Within the United States, at the 1990-2005 population growth rate of 1.1% per year and income growth rate of 1.8% per year, intensity would have had to decline at a rate of -2.9% per year to hold emissions level; however, U.S. intensity declined at a rate of -1.9%, leaving emissions to grow at 1.0% per year. 

Looking to the future, under auspices of the Copenhagen Accord, the United States has submitted a target of reducing emissions from the 2005 level by 17% in 2020. This would require the United States to reduce the intensity of its emissions by some -4.6% per year during the 2010-2020 decade. This implies that the rate of intensity decline needs to better than double. 

Date of Report: March 5, 2010
Number of Pages: 36
Order Number: RL33970
Price: $29.95

Document available electronically as a pdf file or in paper form.