Several studies have estimated the total impact (aggregated across sectors) in different regions of the world. Table 19-4 shows aggregate, monetized impact estimates for a doubling of atmospheric CO₂ on the current economy and population from four studies. Clearly, in all of these studies there are substantial uncertainties about the total impacts to regions and whether some regions will have net benefits or net damages at certain changes in global average temperature. Most studies, however, show the following:

• Developing countries, on the whole, are more vulnerable to climate change than developed countries.
  
• At low magnitudes of temperature change, damages are more likely to be mixed across regions, but at higher magnitudes virtually all regions have net damages.
  
• The distribution of risk may change at different changes in temperature.

Developing countries tend to be more vulnerable to climate change because their economies rely more heavily on climate-sensitive activities (particularly agriculture), and many already operate close to environmental and climatic tolerance levels (e.g., with respect to coastal and water resources). If current development trends continue, few developing countries will have the financial, technical, and institutional capacity and knowledge base for efficient adaptation (a key reason for higher health impacts). For temperature increases of less than 2-3°C, some regions may have net benefits and some may have net damages. If temperature increases more than 2-3°C, most regions have net damages, and damages for all regions increase at higher changes in global average temperature.

Table 19-4: Indicative world impacts, by region (% of current GDP). Estimates are incomplete, and confidence in individual numbers is very low. See list of caveats in Section 19.4.1. There is a considerable range of uncertainty around estimates. Tol's (1999a) estimated standard deviations are lower bounds to real uncertainty. Figures are expressed as impacts on a society with today's economic structure, population, laws, etc. Mendelsohn et al. (2000) estimates denote impact on a future economy. Positive numbers denote benefits; negative numbers denote costs (Pearce et al., 1996; Tol, 1999a; Mendelsohn et al., 2000; Nordhaus and Boyer, 2000).
	IPCC SAR	Mendelsohn et al.		Nordhaus and Boyer	Tol
	2.5°C Warming	1.5°C Warming	2.5°C Warming	2.5°C Warming	1°C Warminga
North America					3.4 (1.2)
- United States			0.3	-0.5
OECD Europe					3.7 (2.2)
- EU				-2.8
OECD Pacific					1.0 (1.1)
- Japan			-0.1	-0.5
Eastern Europe/FSU					2.0 (3.8)
- Eastern Europe				-0.7
- Russia			11.1	0.7
Middle East				-2.0b	1.1 (2.2)
Latin America					-0.1 (0.6)
- Brazil			-1.4
South, Southeast Asia					-1.7 (1.1)
- India			-2.0	-4.9
China			1.8	-0.2	2.1 (5.0)c
Africa				-3.9	-4.1 (2.2)
Developed countries Developing countries	-1.0 to -1.5 -2.0 to -9.0	0.12 0.05	0.03 -0.17
World
- Output weighted	-1.5 to -2.0	0.09	0.1	-1.5	2.3 (1.0)
- Population weighted				-1.9
- At world average prices					-2.7 (0.8)
- Equity weighted					0.2 (1.3)
a Figures in brackets denote standard deviations. b High-income countries in Organization of Petroleum Exporting countries (OPEC). c China, Laos, North Korea, Vietnam.

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