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ecology

A warmer Earth

Increase of the temperature, speeded up by human action, should redraw the profile of life on the planet

Weeks ago, the newspapers of the entire world reported on a study carried out by 19 researchers from eight countries and published in the scientific magazine Nature, foreseeing three worrying scenarios for 50 years from now, as a consequence of the forecast increase in the average global temperature mainly caused by burning forests and fossil fuels. In the best of the three, from 900,000 to 1.8 million species of plants and terrestrial animals, corresponding to 18% of the estimated total of present-day species, run the imminent risk of extinction, if the temperature rises a mere 0.8 to 1.7 degrees Celsius and the concentration of CO2 in the atmosphere rises 30% – a forecast that many specialists hold to be certain, in the light of the refusal of the United States and Russia, the two biggest polluters in the world, to sing up the Kyoto Protocol, intended to reduce the emission of carbon dioxide.

In the most dramatic forecast of the study coordinated by Chris Thomas, from the University of Leeds, in the United Kingdom – with the participation of Brazilian biologist Marinez Ferreira de Siqueira, from the Environmental Information Reference Center (Cria) -, an increase greater than 2 degrees in the temperature threatens the continuity of almost double the species – or even three times more, should the plants and animals not succeed in moving to colder regions and finding other spaces to live in.

The computer programs that led to these conclusions are evidently limited and start off from the assumption that life in future is going to behave as it has done in the past, but any one of the three possibilities represents a new mass extinction – the sixth in the history of the planet – with possible serious implications for the life of human beings. The last time that something similar occurred was 65 million years ago, when an extinction caused by volcanic eruptions, or perhaps asteroids colliding with the planet, eliminated the dinosaurs and the majority of the forms of life on Earth, a long time before the human species arose.

Those who face scalding hot summers may perhaps find it difficult to believe that an increase of 2 degrees is capable of such damage. But this possibility can be taken into consideration because of one detail: the warming up is not homogeneous. “The average rise of 2 degrees may represent an increase of 1 degree in some regions of the planet, but more than 4 or 5 degrees in others”, says Jefferson Cardia Simões, a glaciologist from the Federal University of Rio Grande do Sul (UFRGS).

And, as the more intense heat accelerates the evaporation of the water and alters the rainfall patterns, the environmental imbalances cease to be a theoretical possibility to become concrete problems, as, incidentally, is already happening. In September of last year, a typhoon, the origins of which were attributed to global climatic changes, hit North Korea and left a hundred dead, besides 25,000 homeless.

Chris Thomas’ team analyzed how more or less intense climatic changes can influence the future of 1,103 species of plants and animals, almost all exclusive (endemic) to each one of the six regions rich in diversity – Mexico, Australia, South Africa, Brazil, Costa Rica and Europe -, which correspond to one fifth of the land on the planet. It was the largest sample yet analyzed to understand how climatic changes could affect life on Earth, where according to the most reliable estimates, between 5 million and 10 million species currently live, although only 1.8 million of them have been characterized. Even before this study, there were already indications of changes in the ways in which the species of animals and plants related amongst themselves or with the environment – the so-called ecological relationships – as a consequence of recent climatic changes.

In the last hundred years, 60% of the populations of 35 species of European butterflies that do not show migratory habits have relocated and expanded the geographical area they occupy from 35 to 240 kilometers in the direction of the North Pole, according to a study coordinated by Camille Parmesan, a biologist from the University of Texas, published in Nature in 1999. In another article published in Nature, in 2001, Gian-Reto Walther, a geobotanist from the University of Hannover, Germany, recorded other modifications in ecological relationships, such as the anticipation by two to five days the migration of birds in Europe and North America, or the flowering between 1.5 and 3 days earlier each decade of plants in Europe.

More room for old diseases
The future of our own species could be threatened, in a more direct manner than one may imagine. “Climatic changes can increase the geographical distribution of insects like the Aedes (the transmitter of dengue and yellow fever) and the Anopheles (which transmits malaria) and take tropical diseases to countries from temperate regions”, comments Thomas Lewinson, an ecologist from the State University of Campinas (Unicamp). “Europe may have to concern itself with tropical diseases that it has never known or which had disappeared, like malaria, which was relatively common at the time of the Roman Empire.”

Marcelo Tabarelli, an ecologist from the Federal University of Pernambuco (UFPE), gives an idea of what can happen in a space like the Amazon basin: the disappearance of vegetation and animals caused by climate changes and also by the cutting down of the forest is bound to lead to changes in more than one region of the planet. The water lost by plants by transpiration and by animals by breathing gives rise to masses of air that transfer heat and humidity to neighboring regions. An alteration in this cycle may make the climate of the Cerrado (savanna), in the central region of Brazil, even drier and endanger the cultivation of soybeans, today one of the country’s main export products.

In the Brazilian contribution to the article in Nature, Marinez analyzed what can happen to 163 species of plants, using the database resulting from a partnership between Cria and the Cerrado Biome Technical Cooperation, Conservation and Handling Project, made up by Embrapa Cerrados, the University of Brasilia (UnB), the Brazilian Institute of the Environment and Renewable Natural Resource (Ibama) and the Royal Botanic Garden Edinburgh, Scotland.

Of this total, 123 are endemic to the savanna, which once occupied 18% of the Brazilian territory and is reduced today to one sixth of the original area. In the mildest scenario, with an increase in temperature of between 0.8 and 1.8 degrees, 66 species from this ecosystem would be threatened with extinction, while 75 would run this risk with the temperature of the planet rising 2 degrees.

“Warming makes the environment that favors the survival and reproduction of these species disappear, particularly those that are more sensitive to alterations in the climate”, explains the researcher, whose work was carried out in the ambit of the SpeciesLink project, linked to the Biota-FAPESP Program, funded by the Foundation. Accordingly, it is possible, for example, for two shrubs typical of the savanna, the wild coffee bush (Palicourea rigida) and the cocaine tree (Erythroxylum suberosum), to disappear in a few generations, or to survive for some more time as living-dead species – with specimens that are alive, but incapable of reproducing.

Human pressure
In a way, the rise in the temperature is part of a natural cycle of heating up of the planet, which next begins to cool down again. The problem is that human activities like deforestation and the pollution caused by industry and by automobiles are speeding this process up. 18,000 years ago, at the peak of the most recent glaciation, also known as the last ice age, one third of the Earth was covered by glaciers, and its average temperature was around 9 degrees. In 1900, 66% of this ice had now melted, and the planet was almost 7 degrees warmer.

In the mid 18th century, the level of carbon dioxide in the atmosphere grew 33%, going up from 286 to 373 parts per million by volume, due, in great measure, to the growing consumption of fossil fuels after the Industrial Revolution. In the atmosphere, carbon dioxide forms a sort of blanket that retains the heat reflected by the surface of the planet and makes the existence of life possible. Accordingly, in the right measure, its effect is beneficial. It is when the concentration is very high that the imbalances arise. According to the World Meteorological Organization (WMO), the average surface temperature has increased at least 0.6 degrees just in the last century, at a more intense pace from the 1970’s up until now. It is an increase that is 15 times greater than the average verified in the 180 previous centuries. “The difference lies in the speed that man has imparted to this process”, Simões comments.

For human beings, who have acquired the capacity for making a space comfortable – by pulling up a blanket or switching on the air-conditioning -, five decades seems plenty. But it is a very short time, in the light of the thousands of years that larger species, which grow more slowly, take to adjust to changes in the environment. According to the biologists, it is very improbable that in just half a century plants and animals have time to adapt, from the genetic point of view, to the changes caused by global warming, which aggravates a situation that was already complicated on its own, the ongoing loss of natural environments.

The risk of extinction, Tabarelli points out, should not affect all the species in the same way. Some may perhaps be capable of dispersing in the direction of the poles or to higher altitudes, with more amenable temperatures, while others may even be favored. Probably, those more sensitive to changes in temperature and humidity should be the first to disappear.

“If we act immediately, we can try to remedy the effects of the climatic changes, transferring the more sensitive species to other regions”, suggests ecologist Jean Paul Metzger, from the University of São Paulo (USP). For Simões, from UFRGS, the possibility of the extinction of thousands of species of the planet is above all an ethical question, more than numerical: “Do we have the right to leave the planet without favorable conditions of life for the next generations?”

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