Tropics are on the move (?)
Below is an article summarizing a non-peer-reviewed and unpublished paper which was primarily written by a woman employed by an Australian university Department devoted to climate change (full details of that below). Despite its undistinguished origins, however, it has made the news so I think a few comments are in order.
For a start, she could well be right that the tropical climate zone expanded in recent years. That it might shrink again is her unexamined assumption, however. There WAS global warming in the '80s and '90s and that has more or less plateaued since then, though in the last two years we have seen what seem to be the first signs of a corrective downswing in temperature.
That really is all one needs to say but a couple of minor points just for fun: She characterizes the sub-tropical zone as dry. I live in that zone in Australia, so I wonder if she would like to explain the rain falling outside my window at the moment in what is normally the driest time of the year here (winter)? She seems not to consider that global warming might increase precipitation in ALL areas of the globe -- as it should in theory do (more warmth means more evaporation off the sea and hence more rainfall).
She also concedes that a tropical climate is best for biodiversity -- but seems to imply that that is a bad thing -- an unusual stance for a Greenie!
She also says that disease patterns of the tropics will spead more widely -- completely ignoring that cold weather is a lot more fatal than warm weather and that an expansion of the warm zone should therefore SAVE lives.
She also says that warming will cause more extreme rainfall events in the tropics, with the implication that that is a bad thing. I have news for her. I was born and bred in the middle of an area that CONSTANTLY had extreme rainfall events (Tully to Babinda) and we did quite well there. With around 7 yards of rain a year the crops certainly grew like mad.
I could go on but what is the point in arguing with a religion? -- JR
A review of scientific literature released today by James Cook University shows that the Earth’s tropical zone is expanding and with it the subtropical dry zone is extending into what have been humid temperate climate zones. The authors of the review concluded that the effects of a poleward expansion of the tropical and subtropical zones were immense, resulting in a variety of social, political, economic and environmental implications.
Conducted by Dr Joanne Isaac, Post-Doctoral Fellow at JCU’s Centre for Tropical Biodiversity and Climate Change, with Professor Steve Turton, from JCU’s School of Earth and Environment Sciences, the review looked at scientific findings from long-term satellite measurements, weather balloon data, climate models and sea surface temperature studies.
Professor Turton said that the review - Expansion of the Tropics: Evidence and Implications - encompassed about 70 peer-reviewed scientific papers and reports from scientists and institutions right around the world. The review found that of particular concern were regions which border the subtropics and currently experience a temperate Mediterranean climate. “Such areas include heavily populated regions of southern Australia, southern Africa, the southern Europe-Mediterranean-Middle East region, the south-western United States, northern Mexico, and southern South America – all of which are predicted to experience severe drying.
“If the dry subtropics expand into these regions, the consequences could be devastating for water resources, natural ecosystems and agriculture, with potentially cascading environmental, social and health implications.”
The survey reveals that scientific data suggests while these areas could experience an increased frequency of droughts, the expansion of the tropical zone could result in extreme rainfall events and floods to regions which have not previously been exposed to such conditions, and a poleward shift in the paths of extra-tropical and possibly tropical cyclones in the next 100 years.
“A further implication of the expansion of the tropical zone is the possible expansion of tropical associated diseases and pests.” The review looked at scientific findings in relation to dengue among other tropical diseases and reports that some models predict the greatest increase in the annual epidemic potential of dengue will be into the subtropical regions, including the southern United States, China and northern Africa in the northern hemisphere, and south America, southern Africa, and most of Australia in the southern hemisphere.
The tropical zone is commonly defined geometrically as the portion of the Earth’s surface that lies between the Tropics of Cancer and Capricorn at 23.5 degrees latitude north and south respectively.
Evidence accumulating: “In general, atmospheric scientists estimate the climatic boundaries of the tropics extend further from the equator to around 30 degrees latitude north and south,” the review reports. “In recent years a variety of independent studies, employing different methodologies have found evidence for the widening of the topical region, as defined by climate scientists.
“However, while evidence is accumulating for the widening of the tropical belt and shifts in other climatic events, there is still much uncertainty regarding the degree of the expansion and the mechanisms which are driving it. “For example, across the studies reviewed the estimates of the increase in the tropics vary from 2.0 to more than 5 degrees of latitude approximately every 25 years. That makes the minimum agreed expansion of the Topics zone equivalent to around 300 kilometres. “This variation of estimates makes predicting future shifts difficult. Estimates for the expansion of the tropical zone in next 25 years (assuming the rate of movement is the same as the past 25 years) range from approximately 222 kilometres to more than 533 kilometres depending on which estimate is used.”
The tropics currently occupy approximately 40 per cent of the Earth’s land surface and are home to almost half of the world’s human population and account for more than 80 per cent of the Earth’s biodiversity. The majority of the world’s endemic animals and plants, which are found nowhere else on earth, are found in the tropics and are adapted to the specific climatic conditions found there.
“Thus, the implications of a poleward expansion of the tropical and subtropical zones are immense and the effects could result in a variety of social, political, economic and environmental implications,” the review said.
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