Negishi Welfare Weights: The Mathematics of Global Inequality

The paper argues that Negishi weighting is a critical but often opaque ethical assumption in climate-economics models that effectively freezes the current global distribution of income. By assigning higher weights to the welfare of richer regions, these models suppress the inherent tendency of utilitarian welfare functions to recommend income redistribution from rich to poor regions. The author contends that this creates a political bias in policy advice, as the resulting 'optimal' scenarios are only optimal in a world where income redistribution is considered impossible or forbidden. The document suggests alternatives, including increasing transparency, allowing for redistribution in models, optimizing for money rather than utility, or using non-welfare-optimizing IAMs.

• Negishi weighting is used in regionally disaggregated integrated assessment models (IAMs) to prevent the models from recommending a radical redistribution of world income, effectively maintaining the existing distribution of wealth between regions.
• Without the use of Negishi weights, IAMs that maximize global welfare would naturally suggest equalizing income across regions because of the assumption of diminishing marginal utility of consumption, where a dollar provides more utility to a poor person than a rich person.
• The Negishi procedure achieves its result by assigning higher welfare weights to richer countries and lower weights to poorer countries, ensuring that the weighted contribution to social welfare of an additional dollar is the same across all regions.
• The author identifies a contradiction in these models: they apply the principle of diminishing marginal utility of income inter-temporally (to prioritize the present generation over the future) but suppress it inter-regionally via Negishi weights (to avoid prioritizing poor regions over rich ones).
• The use of technical language, such as 'equalizing the shadow price of capital,' often masks the ethical implication that the welfare of rich regions is being prioritized over that of poor regions, leading to a lack of transparency for policy makers and the public.
• The document proposes four solutions to address the bias and opacity of Negishi weighting: increasing transparency of the weights' impact, discontinuing the weights to allow for redistribution, optimizing for money instead of utility, or utilizing IAMs that do not optimize welfare (such as the PAGE model).

APA

Stanton, E. A. (2009). Negishi Welfare Weights: The Mathematics of Global Inequality. Stockholm Environment Institute. https://www.sei.org/mediamanager/documents/Publications/Climate/negishi-welfare-rights.pdf

Chicago

Stanton, Elizabeth A. Negishi Welfare Weights: The Mathematics of Global Inequality. Stockholm Environment Institute, 2009. https://www.sei.org/mediamanager/documents/Publications/Climate/negishi-welfare-rights.pdf.

Wikipedia

{{cite report |last1=Stanton |first1=Elizabeth A. |title=Negishi Welfare Weights: The Mathematics of Global Inequality |publisher=Stockholm Environment Institute |date=14 May 2009 |url=https://www.sei.org/mediamanager/documents/Publications/Climate/negishi-welfare-rights.pdf |access-date=23 October 2026 |via=Climate Insights Directory}}

BibTeX

@techreport{stanton2009negishi, author = {Stanton, Elizabeth A.}, title = {{Negishi Welfare Weights: The Mathematics of Global Inequality}}, institution = {Stockholm Environment Institute}, year = {2009}, month = may, url = {https://www.sei.org/mediamanager/documents/Publications/Climate/negishi-welfare-rights.pdf}, urldate = {2026-10-23}, note = {Indexed by Climate Insights Directory} }