The change in globally averaged temperature that have occurred at that the Earth’s surface over the past century are similar in size and timing to those【A1】______ by models take into account the combined influences of human factors and solar variability.

To【A2】______ the question of attribution requires the【A3】______ of more powerful and complex methods, beyond the use of global averages alone. New studies have focused on【A4】______ maps or patterns of temperature change in【A5】______ and in models. Pattern analysis is the climatologically equivalent of the more comprehensive tests in the medical analogy mentioned【A6】______ , and makes it possible to achieve more definitive【A7】______ of observed climate changed 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 surface of the Earth and over the whole【A8】______ cycle. Patterns of change over space and time therefore provide a more powerful【A9】______ technique. The basic idea【A10】______ pattern-based approaches is that different【A11】______ causes of climate change have different characteristic patterns of climate response or fingerprints. Attribution studies seek to【A12】______ a fingerprint match between the patterns of climate change【A13】______ by models and those actually observed.

The most recent assessment of the science suggests that human activities have led to a discernible【A14】______ on global climate and that these activities will have and increasing influence on future climate. The burning of coal, oil and natural gas, as well as various agricultural and industrial practices, are【A15】______ the composition of the atmosphere and contributing to climate change. These human activities have led to increased atmospheric【A16】______ 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【A17】______ of small particles in the atmosphere. These particles can change the【A18】______ of energy that is absorbed and reflected by the atmosphere. They are also believed to modify the【A19】______ of air and clouds, changing the amount of energy that they absorb and reflect. Intensive studies of the climate effects of these particles began only recently and the overall【A20】______ 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.