TOP CLIMATE SCIENTISTS SHARE THEIR OUTLOOK

By Tom de Castella 2009-11-26

Name: John Mitchell

Age: 61

Nationality: British

Position: Director of Climate Science, Met Office Expertise: Climate modelling

After 36 years at the Met Office, including a spell writing the shipping forecast, John Mitchell has a weather-beaten mind. In person, there is no smug air of foreknowledge. Yet this softly spoken rugby fan from County Down in Northern Ireland is one of the most experienced climate modellers in the world.

Modelling is a contentious area. There's so much we don't fully understand about the climate – clouds, hurricanes, ice melting, aerosols – that questions remain over the ability of super-computers to model future climate. One experiment – Climateprediction.net, which generated thousands of versions of the Met Office's climate model and got people to run them on their home PCs – showed that models will produce radically different results if you make minor adjustments to their parameters. The week before I met Mitchell, the Met Office was forced to defend its “barbecue summer” press release – proving the difficulty of making even seasonal predictions.

Mitchell takes such criticism calmly. “Essentially, a model is based on Newton's Laws of Motion. All we're trying to do with the models is quantify [the warming] better and say what the regional changes are.”

In practice, that means taking balloon and satellite measurements for temperature, winds and humidity in the atmosphere and using equations to give you a rate of change. It is always going to be an approximate picture but he insists there is a “strong resemblance” with what happens in reality.

Big obstacles remain. “There's so much variation out there,” he says, pointing through the window. “How do you model that? Clouds are the ‘Achilles' heel' of modelling.”

But modelling power is increasing all the time. This summer, the government gave people access to detailed regional climate projections for the coming decades. The modelling was done by the Met Office – and though many scientists are uncomfortable with such “postcode predictions”, saying they send out an overconfident message about our understanding of the future, Mitchell is proud that the US is now considering following suit.

Personal stance: Takes small steps – turning down the thermostat and unplugging his mobile phone charger.

姓名：约翰•米切尔(John Mitchell)

年龄：61

国籍：英国

职位：英国气象局(Met Office)气候科学部主任专长：气候模型分析在英国气象局工作了36年之久（其中有一段时间负责编写海上气候预报），约翰•米切尔的头脑已经饱经风霜。外表来看，他丝毫没有拥有先见之明的自负姿态。然而，这个来自北爱尔兰唐郡、语调温和的橄榄球爱好者，却是世界上最有经验的气候模型分析专家之一。

模型分析是一个有争议的领域。关于气候，我们有太多东西都不是很了解——云团、飓风、融冰、悬浮物，因此对于超级计算机模拟未来气候的能力仍然存在 疑问。根据一项试验，Climateprediction.net网站会生成数以千计的气象局气候模型版本，让人们在自己家里的个人电脑上运行。试验结果 显示，如果你对参数进行轻微的调整，模型就会产生截然不同的结果。我与米切尔会面前一周，英国气象局被迫为其“烧烤夏季”(barbecue summer)的新闻稿进行了辩护——这证明哪怕只是进行季节性预测也很困难。

面对这些批评的声音，米切尔表现得很平静。“本质上，模型的基础是牛顿的运动定律。我们所尝试去做的，不过是利用模型（对气候变暖）进行更好的量化，并说明有哪些地区性变化。”

在实践中，这意味着利用气球和卫星测量温度、气流和大气中的湿度，并用方程式得出变化速率。这永远只会是一种大致的描述，但他坚称这与实际情况“非常相似”。

重大障碍依然存在。“那里的变化实在太多了，”他指着窗外说道。“你怎么对它建立模型？云层就是模型分析的致命弱点。”

但模型分析的能力一直在不断增强。今天夏天，英国政府允许人们获取未来数十年详细的地区气候预测信息。这个模型是由英国气象局建立的——尽管许多科 学家不喜欢这种“邮政编码预测”，称它们就我们对未来的了解传递出一种过于自信的信息，但让米切尔感到骄傲的是，美国正在考虑效仿这种做法。

个人立场：从小事做起——调低自动调温器的功率，不充电时从插座上拔掉手机充电器。

译者/管婧