单选题 The changes in globally averaged temperature that have occurred at the Earth"s surface over the past century are similar in size and timing to those 21 by models that take into account the combined influences of human factors and solar variability.
To 22 the question of attribution requires the 23 of more powerful and complex methods, beyond the use of global averages alone. New studies have focused on 24 maps or patterns of temperature change in 25 and in models. Pattern analysis is the climatologically equivalent of the more comprehensive tests in the medical analogy mentioned 26 , and makes it possible to achieve more definitive 27 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 surface of the Earth and over the whole 28 cycle. Patterns of change over space and time therefore provide a more powerful 29 technique. The basic idea 30 pattern-based approaches is that different 31 causes of climate change have different characteristic patterns of climate response or fingerprints. Attribution studies seek to 32 a fingerprint match between the patterns of climate change 33 by models and those actually observed.
The most recent assessment of the science suggests that human activities have led to a discernible 34 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 35 the composition of the atmosphere and contributing to climate change, These human activities have led to increased atmospheric 36 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 37 of small particles in the atmosphere. These particles can change the 38 of energy that is absorbed and reflected by the atmosphere. They are also believed to modify the 39 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 40 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.