英语翻译We are close to a knowledge of annual summer and winter

　　We are close to （主谓）,knowledge是宾语,以介词短语的形式后跟着定语,
a knowledge of annual summer and winter temperature variations
over much of the northern hemisphere going back 600 years.（这一部分又修饰说明前面的整个长的定语,其中,going back 600 years是后置定语,修饰northern hemisphere）
希望可以说明白!