1 February 2004 | EN | 中文
Biodiversity is inextricably linked to climate, but these interactions are not straightforward. This policy brief examines the interface from both sides. The authors firstly explore the impacts of global warming on biodiversity, from increasing the rate of extinctions to more subtle changes in reproductive cycles and growing seasons.
Turning the tables, they then look at how biodiversity affects climate change. For example, when forests are felled, both local weather and global climate are affected as the removal of trees causes shifts in moisture and temperature, and stored carbon is released to the atmosphere. Similarly, changes in oceanic algal populations can, through a series of natural processes, actually lower air and water temperatures.
With biodiversity and climate change so closely linked, the authors explain why a strong, integrated response is needed, although there are numerous hurdles at the international level. National programmes with a two-pronged approach possibly hold more promise, but even here, governments will need to restructure the way they handle environmental issues before real progress can be made.
A historical context
The Earth’s climate has gone through many periods of significant change throughout its history. Whether they featured warming or cooling, these shifts have inevitably had important ecological impacts: the fossil record shows that episodes of major climate change have coincided with a number of mass extinctions of species over the past 500 million years.
The current episode of global warming, however, is different from the rest, as it is fuelled mostly by human activities – specifically the emission of greenhouse gases, chiefly from burning fossil fuels. Other human activities that contribute to climate change include agriculture and changes in land use that lead to the release of methane, carbon dioxide, nitrous oxide, and some industrially produced gases.
Increased emissions of all these gases are leading to build-up of greenhouse gases in the atmosphere. Carbon dioxide is accumulating faster than at any time over the past 20,000 years. And in the immediate future, rates of increase in global temperatures are expected to be the greatest for the last 10,000 years. 
So today’s warming trend is likely to have a significant impact on species as well as species’ habitats – in short, on biodiversity. But just as we are responsible for the conservation of biodiversity, so we are in a position to limit greenhouse gas concentrations in the atmosphere and help people and ecosystems adapt to the Earth’s changing climate.
How climate change affects biodiversity
Detailed knowledge of how climate change affects biodiversity is still very limited, but recent studies have identified a number of areas where changes from warming are evident. One is what ecologists call ecosystem boundaries. These are the transition zones that separate, say, a prairie made up primarily of tall grasses from one containing mixed grasses. Changes in precipitation and temperature can cause these boundaries to move, allowing some ecosystems to expand into new areas, while others diminish in size as the climate becomes inhospitable to the species they contain.
From a broader perspective, climate change may lead to a sharp increase in rates of extinction. According to one recent study focusing on five regions of the world, if the climate continues to warm it could dramatically increase the number of species going extinct. Mid-range predictions suggest that 24 per cent of species in these regions will be on their way to extinction by 2050 due to climate change. This study also indicates that for many species, climate change poses a greater threat to their survival than the destruction of their natural habitat. 
Climate change also affects species at the level of cells and genes. Changes in the genetic makeup of species are expected as organisms adapt to new climatic conditions, and increases in temperature can also lead to increases in the rate at which cells use energy. 
Other observed impacts of climate change include changes in the timing of reproduction in certain species; in the length of the growing season in many regions; in the abundance of different species; and in the frequency of pest and disease outbreaks. For example, higher temperatures have led to an increase in the number of eggs laid by the spruce budworm, already one of the most devastating pests in North America’s boreal forest. This could in turn contribute to more severe outbreaks of this pest. 
The impacts of climate change on biodiversity will, of course, vary considerably from region to region, partly because changes in temperature and precipitation will differ among regions. The most rapid changes in climate are expected in the far north and south of the planet, and in mountainous regions. Unfortunately, these are also the regions where species often have no alternative habitats, a factor that prevents them – unlike animals and plants in some temperate regions – from migrating or spreading elsewhere to survive.
Other species are vulnerable in different ways. Corals and other organisms living in coral reefs, for example, have already shown devastating losses as a result of increased water temperatures. Species restricted to small areas, or in small populations, are also particularly vulnerable. A catastrophic event such as disease or drought, for example, can kill off a small population. And populations in small, isolated habitats are unlikely to be replenished once decimated by outbreaks of fire or other catastrophes.
How biodiversity affects climate
The process is not one-way. Just as climate change alters the state of biodiversity, so changes in biodiversity can also affect the world’s climate. Perhaps most significantly, changes in land use that lead to a loss of biodiversity can lead to increased greenhouse gas emissions.
Take forests. These are a major store of carbon. Carbon dioxide is released into the atmosphere whenever there are forest fires, or when forests are cut down. It is estimated that one-third of the carbon dioxide released into the atmosphere between 1850 and 1998 came from land-based sources, predominantly the destruction of forests.  Forests also help to regulate moisture in the atmosphere and can reduce temperatures. So felling them can cause changes in atmospheric moisture and higher temperatures.
Peatlands or mires are another major store of greenhouse gases. As they hold roughly one-third of the carbon contained in soil worldwide, greenhouse gases are released into the atmosphere every time wetlands or peatlands are burned, drained, converted to agriculture or degraded. A dramatic example of this was the peatland forest fires that occurred in Indonesia during 1997. These fires released amounts of carbon dioxide equivalent to 40 per cent of the world’s average yearly carbon emissions from fossil fuels. 
There are also feedback mechanisms at work between biodiversity and climate change. For example, some species of ocean algae release a chemical into the atmosphere known as dimethyl sulfate (DMS). When ocean temperatures rise – an effect of global warming – more DMS is released. But DMS is also associated with the formation of clouds. This means that a boom in populations of some algal species – due to increased water temperatures – and a resultant boost in DMS levels, may actually help reduce temperatures because extra cloud cover reduces the amount of heat that reaches the Earth’s surface. 
Integrated policy responses
The many ways in which climate and biodiversity interact are gradually leading researchers and policymakers to the conclusion that working on the two issues together will be more effective than dealing with them separately.
At a practical level, this will mean that the initiatives emanating from the UN Framework Convention on Climate Change (UNFCCC) and Convention on Biological Diversity will need to be put into practice in a more integrated way. Both of these conventions came out of the 1992 Earth Summit in Rio de Janeiro, Brazil.
The climate convention aims to stabilise atmospheric concentrations of greenhouse gases, primarily through negotiation of global agreements such as the Kyoto Protocol, but also by providing guidance to governments on practical ways to adapt to a changing climate. The goals of the biodiversity convention are “the conservation of biological diversity, the sustainable use of its components and the fair and equitable sharing of the benefits arising out of the utilisation of genetic resources”.
Despite their separate objectives, members of the two conventions have been considering ways of working together. The biodiversity convention, for example, has an Ad Hoc Technical Expert Group, which has identified a number of possible areas where links between the two conventions could be strengthened.  Similarly, the secretariats to the climate and biodiversity conventions, as well as the UN Convention to Combat Desertification, have established a joint liaison group to help link up initiatives related to climate change and to biodiversity.
One mechanism that will catalyse stronger links between policymakers working on climate change and biodiversity, and that could also have positive implications for biodiversity, is the Clean Development Mechanism of the Kyoto Protocol. This allows developed countries to invest in emissions-reducing projects in developing countries to obtain credits, which they put towards meeting their own emissions targets. Projects to establish plantations as carbon sinks could be added to the activities under this mechanism. If established in degraded areas and composed of indigenous species, such plantations could become valuable habitats that help to conserve biodiversity.
In practice, however, getting those responsible for implementing the two conventions to work together will not be easy. The conventions have separate constituencies, administration arrangements, negotiators and guiding scientific bodies.
Practical ways to link climate change and biodiversity
Focusing on national programmes may get better results. A small number of practical projects on both biodiversity and climate change are already getting off the ground in several countries. One example is the proposed Greater Addo National Park in South Africa. The park covers a large area with a range of elevations, microclimates and ecosystems. By protecting such a variety of diverse habitats, the park’s planners have factored in the effects of climate change, by ensuring that species can migrate to another safe habitat if climate change adversely affects their present one.
In Vietnam, a project to rehabilitate 12,000 hectares of mangrove forest along the northern coast is creating both a large carbon reservoir and a valuable habitat. Local communities benefit, too, from new fisheries for crabs, shrimp and molluscs, while the mangroves offer vital protection from tropical storms for villages and ecosystems alike. 
Energy production is another area with a strong potential for reducing human impacts on climate change while protecting biodiversity. Currently, about 80 per cent of the global carbon dioxide emissions arising from human activities originate from the generation and use of energy from fossil fuels. Renewable energy is widely seen as a desirable alternative. Indeed, in countries where people use wood for fuel, promoting fuel-efficient stoves and biogas can significantly reduce pressure on forests, and thus conserve carbon.
But some projects that promote renewable energy also have an impact on biodiversity. Large-scale hydropower schemes, for example, can trigger losses of terrestrial and aquatic biodiversity, inhibit fish migration and lead to mercury contamination. [10, 11, 12] They can also be net emitters of greenhouse gases, as submerged soils and vegetation decay, and lead to the release of carbon dioxide and methane.
Similarly, biodiversity conservation should be factored in to the design and location of wind turbines. Birds, including several threatened species, have been killed in wind turbines, but simple design modifications can limit these mortalities. Such risks make it important to take biodiversity issues into account when formulating policies on alternative energy sources.
There remain many unanswered questions about the relationship between biodiversity and climate change. One is the amount of carbon that forests actually draw down and release – something signatories to the UNFCCC need to be able to estimate. To be accurate, these calculations must take into account factors such as pest infestations, forest fires and logging which can lead to carbon release, yet scientists have not worked out precisely how that should be done.
A second question relates to the joint governance of biodiversity and climate change issues. In addition to the conventions on biodiversity and climate change, UN member states are party to many other environmental agreements, including treaties to protect migratory species, regulate trade in endangered species, phase out organic pollutants, slow down the pace of desertification and restore the ozone layer.
So if climate change and biodiversity are ever to be considered in tandem, there must first be a much wider debate on how countries can best fulfil all their environmental obligations. This debate has particular relevance for developing countries – many of which have neither the required expertise, nor the necessary finance, to implement these highly complex international agreements.
In recent years, several alternative models for international environmental governance have been suggested. One possible reform at the national level would be to encourage countries to set up a single body to deal with their obligations under all international environmental agreements. At present, many countries have a separate national organisation handling each concern that have little contact with each other, despite the fact that they may report to the same ministry.
Another area for national-level reform could be in the area of disaster management. For example, countries that are drawing up plans to deal with climate-induced disasters could identify not just vulnerable human settlements, but also the local ecosystems on which they depend. An important element of this highly integrated approach is that it would protect ecosystems not just as economic mainstays of local peoples, but also as havens of biodiversity.
Overall, all environmental issues concern natural systems that are linked in myriad ways. Before long, research and policymaking – both at the national and international level – will need to reflect this interconnectedness.
[The authors would like to thank the reviewers for their comments, and to Ehsan Masood and Saleemul Huq for their support and help.]
Hannah Reid is a research associate with the International Institute for Environment and Development's climate change programme. Balakrishna Pisupati is head of the World Conservation Union's regional biodiversity programme in Asia. Helen Baulch is currently an intern with the International Institute for Sustainable Development.
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Kamal Rai ( Nepal )
18 April 2008
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