11 de janeiro de 2010

Clima versus Tempo

Conforme o prometido, um conjunto de referências sobre a diferença entre clima e tempo. Começa com uma nota da Ambio, a definir a questão, e uma transcrição de uma frase de um artigo respigado pela Climate Ark (vale só pela piada que tem); a referência à ciência que interpreta o tempo frio, do Guardian, não se enquadra no tópico da nota, mas como convém ir lembrando, passo a passo, o que se passa, longe da nossa porta, aí fica; a nota do Wired Science tem de ser lida, como a última do Ambio que aborda a temática da validade dos modelos climáticos, relevante para este tópico:
  • ambio: Meteorologia e clima: "Meteorologia é a ciência que estuda os meteoros, isto é, os fenómenos da atmosfera. A sua mais conhecida aplicação prática é a previsão do tempo, em diferentes escalas, mas sobretudo em pequenos períodos de tempos. Na realidade as previsões a mais de três dias, embora tenham sofrido progressos notáveis, são ainda relativamente pouco fiáveis. O clima estuda o padrão das variações meteorológicas, ou seja, avalia estatístiscamente os elementos meteorológicos num período suficientemente grande para permitir avaliar padrões para lá da elevada variação meteorológica de curto prazo. O período considerado mínimo para a análise climática são trinta anos, sendo a média das observações ao longo de trinta anos que define a normal climatológica."  
  • United Kingdom: If I hear another global warming joke, I'll . . | Climate Ark.: "United Kingdom: If I hear another global warming joke, I'll . . . . . . go completely insane. Climate change doesn’t mean we’ll have lots of lovely weather all the time, you numbskulls" 
  • Britain's cold snap does not prove climate science wrong | Leo Hickman and George Monbiot | Environment | guardian.co.uk: [...]  The ability to distinguish trends from complex random events is one of the traits that separates humans from the rest of the animal kingdom. It is also the basis of all science; detecting patterns, distinguishing between signal and noise, and the means by which the laws of physics, chemistry and biology are determined. Now we are being asked to commit ourselves to the wilful stupidity of extrapolating a long-term trend from a single event." 
  • The science behind the cold weather | UK news | The Guardian: "Although it may be hard to believe, many parts of the northern hemisphere are considerably warmer than usual at the moment. Alaska and much of northern Canada is unseasonably warm for instance, with temperatures 5C to 10C warmer than expected. That still leaves the air a biting –30C (–22F) or so though. Hardly a barbecue winter. North Africa and the Mediterranean basin are warmer than average also, by up to 10C. Elsewhere, such as across northern Europe, temperatures are coming in 5C or so colder than average." 
  • It's freaking cold !Skeptical Science: [...] What the science says... Since the mid 1970s, global temperatures have been warming at around 0.2°C per decade. However, weather imposes it's own dramatic ups and downs over the long term trend. We expect to see record cold temperatures even during global warming. Nevertheless over the last decade, daily record high temperatures occurred twice as often as record lows. This tendency towards hotter days is expected to increase as global warming continues into the 21st Century.  [...] I 
  • Looks like I’m going on FoxNews today because it’s cold outside « Climate Progress: "You can’t deny it’s cold outside in Washington, DC today — any more than you can deny the planet is unequivocally warming and humans are probably the cause of most of that warming, can you? I mean, the fact that it’s cold in early January isn’t news. It’s the friggin’ winter! Oh wait, you say we’re setting records for cold over parts of the country. But if you accept the temperature station data going back over a century that says we’re setting records for cold over a small part of the globe over a short period of time, then you have to accept this very same data over the entire globe over a long period of time, no?"

  • Wired Science . Correlations | PBS: "We climate scientists often hear the case made 'If you can't predict the weather next week, how could you predict the climate in a hundred years?' The answer to the question is hidden in the question. The weather and the climate are not exactly the same thing, and so what you can say about the one and what you can say about the other are also different."  
  • Bad Statistical Reasoning about Weather and Climate : Good Math, Bad Math  Wow, look how hot it is today! How can anyone possible deny global warming? Wow, look how cold it is today! How can those idiots believe in global warming?  These are both examples of confusing weather with climate. That confusion is a typical example of a common statistical error: using aggregate data to draw conclusions about specific individuals, or using a single individual to draw conclusions about an aggregate. Individual data points and aggregates are very different things, and you can't just arbitrarily go from one to another.



PS (14.01.10): Já lá vai o tempo em The Economist estava do outro lado da barricada nas questões das alterações climáticas. Este artigo mereceria ser lido pelo Nicolau Santos, do Expresso, e pelo Professor José Medeiros Ferreira (ver aqui): Green.view: Oscilloscope | The Economist.


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