Although the threat of global warming has been known to the world for decades and all countries and leaders agree that we need to deal with the problem, we also know that the effects of measures, especially harsh measures taken in some countries, would be nullified (抵消) if other countries do not control their emissions. Whereas the UN team on climate change has found that the emissions of carbon dioxide would have to be cut globally by 60% to stabilize the content of coz in the atmosphere, this path is not feasible for several reasons. Such deep cuts would cause a breakdown of the world economy. Important and populous (人口众多的) low or medium-income countries are not yet willing to undertake legal commitments about their energy uses. In addition, the state of world technology would not yet permit us to make such a big leap.
We must, however, find a solution to the threat of global warming early in the 21stcentury. Such a commitment would require a degree of shared vision and common responsibilities new to humanity. Success lies in the force of imaginations, in imaging what would happen if we fail to act. Although many living in cold regions would welcome the global-warming effect of a warmer summer, few would cheer the arrival of the subsequent tropical diseases, especially where there had been none.
The main purpose of this passage is to______.
A. convince people that global warming is a real threat
B. criticize some countries for refusing to cut down emissions harmful to the ozone layer
C. analyze the problem of global warming
D. argue against making deep cuts in emissions