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The greenhouse effect. It's the mechanism warming the world as greenhouse gas levels rise. But it's not all bad. If Earth had no greenhouse effect at all, it would be too cold for us altogether. Just look at frigid, dry Mars.
温室效应是指随着温室气体浓度升高而使全球气候变暖的机制。然而，这也不全是坏消息。如果地球上根本没有温室效应，那将会非常之冷。只要看看寒冷、干燥的火星就明白了。
Many thought that if Mars had a stronger greenhouse effect, it might be more hospitable to life. It's not a crazy idea. Mars has lots of carbon dioxide—much of it frozen. In the past, the CO2 as gas could have been in the atmosphere. And previous studies suggested that a denser CO2 atmosphere could have produced a warm and wet Martian climate.
许多人认为如果火星上也有较强的温室效应，就可能更适宜生命生存。这个想法并不疯狂。火星上有大量的二氧化碳——其中很多是以固态形式存在的。而在过去，二氧化碳可能是以气体的形式存在于大气中。之前的一项研究表明含高浓度二氧化碳的大气会形成一个温暖，潮湿的火星气候。
But a new study throws cold water on that temperate Mars. Researchers ran global, 3D climate simulations for a variety of plausible Martian atmospheres. And even with a much thicker CO2 atmosphere, the greenhouse effect could not have warmed Mars above freezing. The study is in the journal Icarus.
然而一项新的研究却向温和的火星泼了冷水。研究人员用3D技术模拟了火星大气合理的变化引起的气候变化。即使大气中的二氧化碳浓度更高，但温室效应并不能将冰冻的火星暖化。这项研究发表在杂志《伊卡洛斯》上。
Mars has dry canyons and riverbeds, so water must have flowed at some point. But those flows may have been short-lived melting episodes triggered by volcanism or asteroid impacts. Because the idea of a balmy ancient Mars just got iced.
火星表面有干燥的大峡谷和河床，因此在某一时刻肯定有水流经过。但这些河流很可能因火山喷发或者小行星碰撞而消失，成为昙花一现。因此关于温和的古代火星这个说法也被冰封了。
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