3．Greenhouse gas emissions would rise if all farms in England and Wales went organic.Though the emissions of each farm would go down，much more food would have to be imported，as the amount they would produce would decrease greatly.
"The key message from my perspective is that you can't really have your cake and eat it，" says Laurence Smith，now at the Royal Agricultural University in the UK，who was part of the team that ran the numbers.Smith is a supporter of organic farming and says "there are a lot of
merits of the organic approach"，but his analysis shows that organic farming has downsides too.
Farming and changes in land use，such as cutting down forests，are responsible for a third of all greenhouse gas emissions.That means reducing farming emissions and the land needed for farming is required to limit further global warming.
Smith and his colleagues found that emissions per unit of food are，on average，20 per cent lower for organic crops and 4 per cent lower for organic animal products.However，organic harvests per hectare （公頃） are also lower on average.For wheat and barley，for instance，harvests are just half of those of conventional farms.This means 1.5 times as much land would be needed to grow the same amount of these foods.
The estimated increase in emissions varies greatly，depending on where the extra farmland comes from.If only half comes from turning grassland into farms，the increase could be as low as 20 per cent.If grassland that would otherwise have been reforested is turned into farmland，emissions could nearly double.
This doesn't necessarily mean people should stop eating organic produce，says Smith.People might choose organic food for other reasons，such as to reduce their pesticide exposure （though contrary to popular belief，organic farmers do use pesticides） or for the sake of wildlife.
Going 100 per cent organic could also harm global biodiversity.The extra land used for farming would mean the land available for wildlife would be smaller and more fragmented （碎片化的）.
Smith says the best option may be to use some organic and conventional farming methods at the same time.
（1）Why may greenhouse gas emissions increase if a country goes organic？
A．Organic farms take longer to build.
B．The agricultural output will increase greatly.
C．The emissions of each farm unit will increase.
D．Greater demand for imported food will be created.
（2）What does the underlined word "merits" in Paragraph 2 probably mean？
A．Changes.
B．Challenges.
C．Advantages.
D．Differences.
（3）What did Smith and his colleagues find？
A．Organic harvests per unit are greater than traditional harvests.
B．Organic farming needs more farmland to feed a country.
C．Global warming could be brought under control.
D．Land was not used in a responsible way.
（4）What is Smith's proposal？
A．Stopping using pesticides.
B．Eating less organic produce.
C．Going back to traditional farming.
D．Adopting mixed farming methods.
