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Frequência de secas está a aumentar. Ou não?

Devido à importância Global e Determinante do Tema para o Futuro do País, este artigo no Público de hoje por Ricardo Garcia, é publicado juntamente com um artigo no Guardian de ontem …
António Sérgio Rosa de Carvalho.
Por Ricardo Garcia in Público
Para quem tem dúvidas sobre o que as alterações climáticas podem significar para as secas em Portugal, o histórico dos últimos 70 anos pode ser um primeiro sinal de alerta. Pelo menos um estudo sugere que as secas se tornaram mais frequentes a partir da década de 1970. E esta tendência coincide com um período de aquecimento no país, após 30 anos de arrefecimento - de 1940 a 1970.
Entre 1941 e 2006, em três quartos das estações meteorológicas do país os episódios de seca concentraram-se a partir de 1976, momento a partir do qual as temperaturas voltaram a subir, segundo um estudo de Vanda Cabrinha Pires, Álvaro Silva e Luísa Mendes, do Instituto de Meteorologia.
De acordo com o estudo, houve nove períodos expressivos de secas desde 1941. A de 1943-46 foi a mais longa. A de 2004-2006 foi a mais intensa e teve a maior extensão territorial, atingindo 100% de Portugal continental. Houve ainda secas expressivas em 1948-49, 1964-65, 1974-76, 1980-83, 1990-92, 1994-95 e 1998-99.
O estudo recua até 1901, calculando um índice usado para medir a seca, o PDSI (Palmer Drought Severity Index), para quatro estações meteorológicas - Lisboa, Porto, Évora e Beja. São mais numerosos os momentos em que o índice aponta para períodos com menos chuva do que para momentos chuvosos - ou seja, as secas podem até estar a tornar-se mais frequentes, mas são uma realidade de longa data no país.
"É um fenómeno intrinsecamente natural. Mas a sociedade está menos capaz de resistir à adversidade natural", afirma Maria Manuela Portela, investigadora do Instituto Superior Técnico (IST).
Chegar a uma conclusão sólida sobre o aumento ou não da frequência das secas requer mais estudos. "A pergunta é complicada. Dar uma resposta com certeza científica não é fácil", afirma João Filipe Santos, professor do Instituto Politécnico de Beja e também investigador no IST.
Um dos problemas está no facto de os estudos se basearem em índices - que são uma forma indirecta de se descrever um fenómeno. Através de um indicador diferente do PDSI, o SPI, João Santos avaliou a distribuição das secas no tempo e no espaço, com base em séries de dados de 144 estações meteorológicas, de 1901 a 2004. Uma das conclusões a que chegou foi a de que o país está claramente dividido. "A seca assume comportamentos diferentes no Norte, no Centro e no Sul", afirma. "O Sul é sempre mais afectado, quer em área, quer em termos de severidade", salienta.
A outra conclusão é a de que a frequência das secas também será diferente conforme a região do país. No Sul, o estudo identificou uma periodicidade de 3,6 anos; no Norte, as secas estariam associadas a um ciclo de 13,4 anos. São, no entanto, resultados preliminares que necessitam de mais estudos.
Numa investigação posterior, Maria Manuela Portela, João Santos e mais três investigadores sugerem limiares de chuva, mês a mês, abaixo dos quais haverá situações de secas. A ministra da Agricultura, Mar, Ambiente e Ordenamento do Território, Assunção Cristas, tem advogado que o país deve ter estratégias de adaptação para mais secas no futuro. Os investigadores Vanda Pires, Álvaro Silva e Luísa Mendes parecem concordar, dizendo, no seu estudo, que o incremento na frequência das secas "é indicativo de um aumento do risco e da vulnerabilidade a este fenómeno, o que poderá obviamente trazer um aumento dos impactos". Ricardo Garcia

Death threats, intimidation and abuse: climate change scientist Michael E. Mann counts the cost of honesty
Research by Michael E. Mann confirmed the reality of global warming. Little did he know that it would also expose him to a vicious hate campaign

Robin McKie, Saturday 3 March 2012 11.32 GMT
Article history

Research by US physicist and climatologist Michael E. Mann demonstrating an increase in global temperatures infuriated climate change deniers. Photograph: Greg Rico
The scientist who has borne the full brunt of attacks by climate change deniers, including death threats and accusations of misappropriating funds, is set to hit back.

Michael E. Mann, creator of the "hockey stick" graph that illustrates recent rapid rises in global temperatures, is to publish a book next month detailing the "disingenuous and cynical" methods used by those who have tried to disprove his findings. The Hockey Stick and the Climate Wars is a startling depiction of a scientist persecuted for trying to tell the truth.

Among the tactics used against Mann were the theft and publication, in 2009, of emails he had exchanged with climate scientist Professor Phil Jones of East Anglia University. Selected, distorted versions of these emails were then published on the internet in order to undermine UN climate talks due to begin in Copenhagen a few weeks later. These negotiations ended in failure. The use of those emails to kill off the climate talks was "a crime against humanity, a crime against the planet," says Mann, a scientist at Penn State University.

In his book, Mann warns that "public discourse has been polluted now for decades by corporate-funded disinformation – not just with climate change but with a host of health, environmental and societal threats." The implications for the planet are grim, he adds.

Mann became a target of climate deniers' hate because his research revealed there has been a recent increase of almost 1°C across the globe, a rise that was unprecedented "during at least the last 1,000 years" and which has been linked to rising emissions of carbon dioxide from cars, factories and power plants. Many other studies have since supported this finding although climate change deniers still reject his conclusions.

Mann's research particularly infuriated deniers after it was used prominently by the UN's Intergovernmental Panel on Climate Change (IPCC) in one of its assessment reports, making him a target of right-wing denial campaigners. But as the 46-year-old scientist told the Observer, he only entered this research field by accident. "I was interested in variations in temperatures of the oceans over the past millennium. But there are no records of these changes so I had to find proxy measures: coral growth, ice cores and tree rings."

By studying these he could trace temperature fluctuations over the past 1,000 years, he realised. The result was a graph that showed small oscillations in temperature over that period until, about 150 years ago, there was a sudden jump, a clear indication that human activities were likely to be involved. A colleague suggested the graph looked like a hockey stick and the name stuck. The results of the study were published in Nature in 1998. Mann's life changed for ever.

"The trouble is that the hockey stick graph become an icon and deniers reckoned if they could smash the icon, the whole concept of global warming would be destroyed with it. Bring down Mike Mann and we can bring down the IPCC, they reckoned. It is a classic technique for the deniers' movement, I have discovered, and I don't mean only those who reject the idea of global warming but those who insist that smoking doesn't cause cancer or that industrial pollution isn't linked to acid rain."

A barrage of intimidation was generated by "a Potemkin village" of policy foundations, as Mann puts it. These groups were set up by privately-funded groups that included Koch Industries and Scaife Foundations and bore names such as the Cato Institute, Americans for Prosperity and the Heartland Institute. These groups bombarded Mann with freedom of information requests while the scientist was served with a subpoena by Republican congressman Joe Barton to provide access to his correspondence. The purported aim was to clarify issues. The real aim was to intimidate Mann.

In addition, Mann has been attacked by Ken Cuccinelli, the Republican attorney general of Virginia who has campaigned to have the scientist stripped of academic credentials. Several committees of inquiry have investigated Mann's work. All have exonerated him.

Thousands of emails have been sent to Mann, many deeply unpleasant. "You and your colleagues… ought to be shot, quartered and fed to the pigs along with your whole damn families," said one. "I was hopin [sic] I would see the news and you commited [sic] suicide," ran another.

Yet all that Mann had done was publish to a study suggesting, in cautious terms, that Earth had started to heat up unexpectedly in the past few decades.

"On one occasion, I had to call the FBI after I was sent an envelope with a powder in it," Mann adds. "It turned out to be cornmeal but again the aim was intimidation. I ended up with police security tape all over my office doors and windows. That is the life of a climate scientist today in the US."

Mann insists he will not give up. "I have a six-year-old daughter and she reminds me what we are fighting for." Indeed, Mann is generally optimistic that climate change deniers and their oil and coal industry backers have overstepped the mark and goaded scientists to take action. He points to a recent letter, signed by 250 members of the US National Academy of Science, including 11 Nobel laureates, and published in Science. The letter warns about the dangers of the current attacks on climate scientists and calls "for an end to McCarthy-like threats of criminal prosecution against our colleagues based on innuendo and guilt by association, the harassment of scientists by politicians seeking distractions to avoid taking action, and the outright lies being spread about them."

"Words like those give me hope," says Mann.

The Hockey Stick and the Climate Wars will be published by Columbia University Press in April

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