一种保守的估计提出到2015年前每年投资500亿美元，到2020年及以后则增加到1000亿美元 — — 这一提案之所以有可能被采纳也正是因为它比较保守。
One conservative estimate – which has a reasonable chance of being accepted precisely because it is conservative – calls for $50 billion per year as of 2015, increasing to $100 billion by 2020 and beyond.