全球气候变暖研究中的不确定性

讨论了有关全球变暖研究中存在的一些不确定性 ,主要包括 3个方面 ,即资料方面的不确定性 ,气候变化机制方面的不确定性和预测方面的不确定性。城市热岛效应是资料中最大的误差来源 ,特别是一些最近几十年快速发展的城市 ,其热岛效应的误差没有很好地得到检查和排除。资料覆盖面也很不完善。地面观测温度在 1979— 1999年的趋势是 0 19℃ / 10a ,但覆盖全球的卫星观测资料(反映对流层低层到中层 )趋势只有 0 0 6℃ / 10a。北极地区的温度变化也没有设想的那样强烈。使用海表温度比使用海表气温得到的变暖估计值偏高。 1979年以来 ,用气温代替海温 ,趋势只有0 13℃ / 10a。海洋在气候变化中的作用需要更深入地研究。利用代用资料来估计全球温度的变化 ,带来的不确定性较大 ,特别是树木年轮 ,因为CO2 浓度的增加可以加速植物的生长 ,其年轮宽度并不一定主要反映与温度的关系。未来气候变化的预测有很大的不确定性 ,到 2 10 0年全球平均气温达+1 4℃～ +5 8℃的估计很可能偏高。

UNCERTAINTIES IN THE GLOBAL WARMING STUDIES

Uncertainties in the global warming studies are discussed in the present paper. These uncertainties are related to some shortcomings in (a) the data used to establish the global temperature series, (b) the mechanism of global climate change, and (c) the scientific understanding of the observed climate elements, including the variability, the appropriate parametrization, and the reproducing in the climate simulation. Based on those factors, the projection of future climate is made. As to the data, the biggest problem is the urban|heat|island effect in the temperature records, temperature measurements made in rapidly growing cities may be distorted by this kind of human|induced excessive heat. This gives a false impression of long|term warming. Although the urban adjustment is often applied, there are still considerable errors. The thorough correction is very difficult, since there are non|stable urbanization effect all over the world and at all times. For example, the manifestations of false warming appeared in the big cities in China were due to the rapid development and population expanding since the late 1970s. These human|induced temperature increases have not been corrected prior to getting the global means. Another uncertainty comes from the uneven coverage in surface temperature records. In the polar regions and in the vast areas of the oceans there are still lack of proper measurements. While the surface record was registering a global warming of 0.19 ℃/10 a between 1979 and 1999, the satellite Microwave Sounding Unit (MSU) record was showing a quite different trend (0.06 ℃/10 a) for the same period. There are significant difference between the sea surface temperature (SST) and the marine air temperature. When we substitute the marine air temperature for SSTs, the global warming trend decreases to 0.13 ℃/10 a. Temperature changes inferred from the proxy data often are different from one another, the uncertainties caused by the low accuracy often confuse the temperature variations which is in the order of 1 ℃ in the Holocene. Another major source of uncertainty in the proxy data comes from the assumption of stable plant growth-CO 2 relation at all times, but we now know it is wrong, rising level of CO 2 enhances the plant growth effectively. The difference between the surface record and the MSU record (which represents the low|middle troposphere) as well as the lower|than|expected polar warming show that there are unknown mechanism involved in the climate system. Role played by the oceans remains an open question. Recent estimate of future temperature increase is in the range of +1.4 ℃ to +5.8 ℃ by 2100 . However, our ability to quantify the human influence on global climate and to exactly forecast the 21st climate is limited because there are uncertainties in these key factors.