Science Literature

One only has to visit a tropical rainforest to discover a world filled with abundant treasures. It is entirely natural for people to want to protect these regions from any threat. Climate change has been perceived as a threat: cooler climates do not support tropical ecozones - but what about warmer climates? Concerns have been raised about plants being unable to adapt to the heat, and there are potential dangers of rainfall reductions. Geological research has revealed a remarkable period of Earth history at the Paleocene-Eocene Boundary, a very warm period known as the Paleocene-Eocene Thermal Maximum (PETM). Although this has been much studied, little is known of the way the tropics responded to high temperatures globally (temperatures rose by about 5 degrees C) and to higher levels of carbon dioxide (perhaps 2.5 times the present level). One point that is agreed is that this rise in global temperatures was geologically rapid: "one of the most abrupt global warming events of the past 65 million years". New research concludes that, fat from being compromised by heat stress, the tropical regions coped very well.

"Most scientists have assumed that, as carbon dioxide levels increase and the Earth warms, plant species diversity in the rainforests will start to dwindle, with plants unable to adapt to the heat. But a new study suggests that the opposite may be true. In the past, rising atmospheric carbon dioxide and higher temperatures actually drove the evolution of far greater numbers of new rainforest plant species than were wiped out."

Although the study says the Amazon can adapt to a warmer world, it still faces an extreme threat from deforestation. (Image: Gerd Ludwig/Corbis, Source here)

The fieldwork was located in Columbia and Venezuela and led by Carlos Jaramillo, a palaeobiologist at the Smithsonian Tropical Research Institute in Panama, In the late Paleocene, the northern Andes had not been uplifted and most of Central America was still underwater. Pollen recovered from cores was used to gain an understanding of the plants growing at the time.

"To find out how this ancient climate change affected rainforest plants, Jaramillo and his team analysed fossilized pollen trapped in rock cores from rainforests in Colombia and Venezuela. They spent seven years locating appropriate sites and taking samples, then used a battery of dating techniques to ensure that they were examining cores formed before, during and after the thermal maximum - a relatively narrow time window in geological terms. The results are published this week in Science."

The findings were an eye-opener. The researchers were expecting the abrupt warming event to have had adverse effects. However, Jaramillo is reported as saying: "we didn't find any extinction event [in plants] associated with the increase in temperature, we didn't find that the precipitation decreased". Furthermore, diversity increased.

"Although some plant species disappeared, many more new species arose. That included entire families, suggesting that the increased temperatures and carbon dioxide levels actually boosted biodiversity. "What we found was exactly the opposite of what we were expecting," says Jaramillo. "The diversity of the tropical forest increased really fast over a very short amount of time.""

With hindsight, the research outcomes are not so surprising. The authors point out in their paper that "Greenhouse experiments have shown that high levels of CO2 together with high levels of soil moisture improve the performance of plants under high temperatures, and it is possible that higher Paleogene CO2 levels contributed to their success." Fieldwork undertaken in forests has documented increased rates of growth that correlate with increased CO2 concentrations in the atmosphere (go here). The implication is that tropical forests are not as fragile and vulnerable to climate change as many have suggested.

"Indeed, it is possible that rainforest families in general, which have been present in the Neotropics since the Paleocene, have the genetic variability to cope with high temperatures, CO2, and rainfall."

Whilst these conclusions have primary applications in the fields of ecology and the environment, this blog is written to point out the relevance for a design-orientated perspective on the natural world. The clue is in the concept of "genetic variability" that enables animals and plants to adapt to environmental change. Within the Design paradigm, animals and plants are designed to adapt because the world's environments experience change. (Speciation, however, can often lead to a loss of genetic variability, which is why some species reach a state where environmental change threatens them with extinction.) This paradigm expects negative feedback mechanisms to be dominant in ecological systems (as pointed out here and here) so that perturbed systems are restored to an equilibrium state.

There is an important application to all this. Design thinking is relevant to many contemporary issues affecting human societies and the world's environments. I should add that there is no party line on such issues, and every view expressed is ultimately a personal view. Climate models have been developed that incorporate significant positive feedback mechanisms - allowing them to predict avalanche scenarios (whether heating or cooling). This has been accompanied by a strong emphasis on the fragility of the Earth's ecosystems - with consequent apocalyptic scenarios much loved by the media. These emphases have led to the politicisation of science, with climate scientists and many others advocating the expenditure of large sums of money to "save the planet". A design perspective allows us to look at the scientific evidence more dispassionately - and there are good reasons for rejecting climate models with large positive feedback parameters. It also allows us to have more confidence in the self-regulating character of the natural world. We recognise that climate change has always been an aspect of history, so adaptation to a changing world is the way forward.

Having said this, there is no doubt that human activity is affecting the Earth's ecozones in a damaging way. The biggest threat to tropical rainforests is not climate change but unmanaged logging. Governments are often complicit in this, and consumers are at fault whenever wood is purchased without any evidence that is from a managed forest source. Instead of blaming the consumption of fossil fuels, those concerned about tropical rainforests would do well to ensure the wood they purchase has the FSC trademark (or similar).

"Jaramillo believes that there is a more pressing threat to the diversity of tropical rainforests. "Deforestation is the real enemy," he says, "not the increase in temperature and carbon dioxide." "

Effects of Rapid Global Warming at the Paleocene-Eocene Boundary on Neotropical Vegetation
Carlos Jaramillo, Diana Ochoa, Lineth Contreras, Mark Pagani, Humberto Carvajal-Ortiz, Lisa M. Pratt, Srinath Krishnan, Agustin Cardona, Millerlandy Romero, Luis Quiroz, Guillermo Rodriguez, Milton J. Rueda, Felipe de la Parra, Sara Moron, Walton Green, German Bayona, Camilo Montes, Oscar Quintero, Rafael Ramirez, German Mora, Stefan Schouten, Hermann Bermudez, Rosa Navarrete, Francisco Parra, Mauricio Alvaran, Jose Osorno, James L. Crowley, Victor Valencia, and Jeff Vervoort.
Science, 330, 12 November 2010: 957-961

Abstract: Temperatures in tropical regions are estimated to have increased by 3 [deg] to 5[deg]C, compared with Late Paleocene values, during the Paleocene-Eocene Thermal Maximum (PETM, 56.3 million years ago) event. We investigated the tropical forest response to this rapid warming by evaluating the palynological record of three stratigraphic sections in eastern Colombia and western Venezuela. We observed a rapid and distinct increase in plant diversity and origination rates, with a set of new taxa, mostly angiosperms, added to the existing stock of low-diversity Paleocene flora. There is no evidence for enhanced aridity in the northern Neotropics. The tropical rainforest was able to persist under elevated temperatures and high levels of atmospheric carbon dioxide, in contrast to speculations that tropical ecosystems were severely compromised by heat stress.

See also:

Milton, J. Rapid warming boosted ancient rainforest, Nature News, 11 November 2010 | doi:10.1038/news.2010.604