Air Pollution as a Climate Forcing: A Workshop

Day 2 Presentations

Some Evidence for Regional Climate Effects in China

Yunfeng Luo
Department of Earth Sciences, National Nature Sciences Foundation of China, Beijing, China

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Figure 1: Inter-annual variation of mean aerosol optical depth in China

Abstract

Since the 1950s, the concentrations of tropospheric aerosols have been increasing noticeably. The uncertainties of aerosol properties, distribution and variation, and its climate effect are now an urgent and important scientific problem, especially for developing countries.

China, the largest developing country in the world, has been using coal as its major energy supply for many years. In addition, mineral aerosols, derived from northwest arid or semi-arid areas of China, usually impact the environment and climate of east China and adjacent areas. This makes China one of the areas polluted heavily by aerosols. However, we still lack a quantitative and comprehensive understanding about the geographical distribution and temporal variation of aerosols over China.

Figure 2: Four months (Jan., Apr., July, Oct.) averaged surface air temperature response

In this paper, by using the direct solar radiation and other conventional observational data, the yearly and monthly mean aerosol optical depths (AOD) at 0.75 -µm were retrieved at 46 solar radiation stations over China from 1961 to 1990. It was found that the AOD increased dramatically over China mainland from 1961 to 1990, particularly in the middle and lower reaches of the Yangzi River area and the east part of southwest China in regions of rapid economic development. The yearly mean AOD has a pattern related to the geographical features, with maxima over basins. In most areas of China the maximum of AOD occurs in spring, but the season of reaching the minimum varies from region to region. The monthly mean AOD distributions are similar to the annual mean pattern, having a strong "basin" effect, but the month-to-month differences are still obvious.

Figure 3: Distribution of linear trend of yearly temperature in China during the period from 1952 to 1990 (10-2°C/year) (Chen et al., 1991)

Based on the retrieved AOD distribution and variation patterns, the aerosol direct radiative forcing and regional climate response in China from 1980-1990 were simulated using a regional climate model. The results show that the mean-value of aerosol direct radiative forcing for China varied between -5.3 W/m and -13 W/m with season. The geographical and temporal distribution of aerosol radiative forcing is generally consistent with that of aerosol optical depth. The surface temperatures are generally reduced in China continent due to the effect of aerosol radiative forcing. The most remarkable regions of surface temperature change are related not only to the magnitude of radiative forcing, but also to general circulation. The simulated surface air temperature response is similar to the real temperature change.

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