（清华大学2008年试题） The changes in globally averaged temperature that have occurred at the Earth’s suce over the past century are similar in size and timing to those【1】by models that take into account the combined influences of human factors and solar variability. To【2】the question of attribution requires the【3】of more powerful and complex methods, beyond the use of global averages alone. New studies have focused on【4】maps or patterns of temperature change in【5】and in models. Pattern ysis is the cli-matologically equivalent of the more comprehensive tests in the medical ogy mentioned【6】, and makes it possible to achieve more definitive【7】of observed climate changes to a particular cause or causes. The expected influence of human activities is thought to be much more complex than uniform warming over the entire suce of the Earth and over the whole【8】cycle. Patterns of change over space and time therefore provide a more powerful【9】technique. The basic idea【10】pattern-based approaches is that different【11】causes of climate change have different characteristic patterns of climate response or fingerprints. Attribution studies seek to【12】a fingerprint match between the patterns of climate change【13】by models and those actually observed. The most recent assessment of the science suggests that human activities have led to a discernible【14】on global climate and that these activities will have an increasing influence on future climate. The burning of coal, oil and natural gas, as well as various agricultural and industrial practices, are【15】the composition of the atmosphere and contributing to climate change. These human activities have led to increased atmospheric【16】of a number of greenhouse gases, including carbon dioxide, methane and so on in the lower atmosphere. Human activities, such as the burning of fossil, have also increased the【17】of small particles in the atmosphere. These particles can change the【18】of energy that is absorbed and reflected by the atmosphere. They are also believed to modify the【19】of air and clouds, changing the amount of energy that they absorb and reflect. Intensive studies of the climatic effects of these particles began only recently and the overall【20】is uncertain. It is likely that the net effect of these small particles is to cool the climate and to partially offset the warming of increasing concentrations of greenhouse gases. 【15】