资料题：Why dose Zhao Baige cite the research by Thomas Wire of London School of Economics in the last paragraph?

COPENHAGEN: Population and climate change are intertwined but the population issue has remained a blind spot when countries discuss ways to mitigate climate change and slow down global warming, according to Zhao Baige,vice minister of National Population and Family Planning Commission of China (NPFPC)"Dealing with climate change is not simply an issue of CO2 emission reduction but a comprehensive challenge involving political, economic, social, cultural and ecological issues, and the population concern fits right into the picture," said Zhao, who is a member of the Chinese government delegation.Many studies link population growth with emissions and the effect of climate change."Calculations of the contribution of population growth to emissions growth globally produce a consistent finding that most of past population growth has been responsible for between 40 percent and 60 percent of emissions growth," so stated by the 2009 State of World Population, released earlier by the UN Population Fund.Although China's family planning policy has received criticism over the past three decades, Zhao said that China's population program has made a great historic contribution to the well-being of society. As a result of the family planning policy, China has seen 400 million fewer births, which has resulted in 18 million fewer tons of  emissions a year, Zhao said.The UN report projected that if the global population would remain 8 billion by the year 2050 instead of a lttle more than 9 billion according to medium growth scenario, "it might result in 1 billion to 2 billion fewer tons of carbon emissions"Meanwhile, she said studies have also shown that family planning programs are moreefficient in helping cut emissions, citing research by Thomas Wire of London School ofEconomics that states: "Each $ 7 spent on basic family planning would reduce  emissions by more than one ton whereas it would cost $ 13 for reduced deforestation, $ 24 to use wind technology, $ 51 for solar power, $ 93 for introducing hybrid cars and $ 131 electric vehicles". She admitted that China's population program is not without consequences, as the country is entering the aging society fast and facing the problem of gender imbalance.