Biodiversity & climate change

For a long time, climate change was regarded as our most pressing environmental concern. However, widespread damage to the Earth’s biodiversity and a hotter planet combined are changing the lives of plants and animals in ways we are only just beginning to understand. Professor Colin Prentice from Imperial College London and Dr. Cosima Porteus from the University of Exeter discuss the implications of climate change for biodiversity, and why we need better models to assess risk to life on Earth.


Pr. Colin Prentice,

Imperial College London (United Kingdom)


Dr. Cosima Porteus,

University of Exeter (United Kingdom)

Pr. Colin Prentice

The recent IPBES report makes it clear that, among the threats to biodiversity, the number one issue is habitat loss. So far, we have not actually seen all that much climate change impact on biodiversity. What we know is that species – plants, birds, fish and so on – are adapting, which is good news. The biosphere is reacting fast, but it has to, because climate change is happening fast.

Dr. Cosima Porteus

I have been studying ocean acidification. Oceans are doing us a huge favor, absorbing carbon and dampening the effects of climate change on earth. But, in the process, the oceans are becoming more acidic, and that affects fish – they lose their sense of smell.

For our research, we used end-of-century projections for carbon dioxide (CO2) in European sea bass. Through an experimental process putting sea bass either in seawater with current levels of carbon dioxide, or those replicated for the end of the century, we found that their sense of smell was reduced by up to half in high carbon dioxide seawater. This is important since fish use their sense of smell to locate food, to avoid predators, to find and choose mates, and larvae use it to find appropriate habitats. For some species, such as salmon, it is used for long-distance migration. This loss of smell is not happening yet – but the message is we have to reduce carbon emissions now.

Pr. C.P.

The fact is, humans have made many species extinct. We know for sure from the paleorecord that, with the exception of large mammals, biodiversity has quite extraordinary resilience if you look back to previous periods of relatively rapid warming. It is often said that in the past, change was much slower, and that now it is much quicker. In fact, when we came out of the last ice age, the process may have been long, but the final warming-up that made the difference was completed in twenty years. The point is, somehow species coped with it. The joker in the pack is that we live in a very different, much more fragmented, landscape. We are not allowing natural biodiversity to be expressed fully – we are putting restrictions on it. We should not be complacent and think that species will naturally migrate through landscapes that look like Iowa, with its corn and soybeans. So, if you ask me, what will happen in the future, exactly, I do not know – it is extremely unclear. For the carbon cycle, our models differ greatly. They are all reasonably well tuned to look at something like the real world today, but, for the future, they go off in different directions. It depends, of course, on the assumptions you make. Our models are not being stretched enough, they are being used to track emissions, but they are not being used to ask ‘what if’ questions, which would be the most relevant. It is a symptom of silo thinking. There are people who study the past, and people who study the present, and they barely talk to each other. If we are talking about a +4°C scenario, I do not think we know what the world would look like. We may not particularly wish to find out, but the fact is we do not know.


of total greenhouse gas emissions from human activities derive from agriculture, forestry and other land use.

Source: IPCC (Climate Change and Land, 2019)

Dr. C.P.

We need to know more about how different stresses combine and interact. Ocean acidification is just one stress on fish populations in addition to the increase in sea temperature and the potential drop in oxygen. Warmer temperatures may produce smaller fish because the fish have less energy available for growth. Fish also move to cooler waters – that could impact fish availability. At the moment, 50% of our fish consumption comes from wild stock. The fact is, we will have to rely more on aquaculture for our food in the future. The FAO is predicting that aquaculture will have to double by 2050 to keep up with population growth, but we have a CO2 problem in aquaculture as well, since where water is recirculated, CO2 tends to accumulate to much higher levels, up to forty times higher. That can affect growth in fish. We are now working with industry partners to find out how we can mitigate this.

500 GtCO2

Over the past 200 years the oceans have taken up 500 GtCO2¹⁴ from the atmosphere out of 1300 GtCO2 total anthropogenic emissions.

Source: IPCC (Special Report on Carbon dioxide Capture and Storage, 2018)

$1.5 trillion

The world’s ‘blue economy’ is worth an estimated $1.5 trillion – that includes offshore oil and gas, tourism, maritime equipment and activity at ports. More than 250 million people worldwide rely on fishing and aquaculture for their livelihoods.

Source: OECD (estimate for 2010), WorldFish (2019)


Biodiversity & climate change

Forests, especially tropical ones, host a wide diversity of plant and animal species, and store large amounts of carbon taken up from the atmosphere. As a consequence, deforestation has serious impacts for both climate change and biodiversity loss. To better understand the processes at work, we spoke to two researchers studying tropical forests, deforestation and climate change.


Dr. Vincent Gauci,

Birmingham University (United Kingdom)

We have seen very significant deforestation in recent years to make way for crops such as oil palm or acacia. What is the effect on biodiversity?

Dr. Vincent Gauci

The character of the landscape changes dramatically, from many hundreds of different plant species per hectare to maybe one or two. With oil palm, we have also seen proliferation of rats – so there is a whole range of other species coming in. We know there has been a 50% loss in orangutans over the last twenty years due to deforestation and we are down to the last 300 or so Sumatran tigers in the wild. It has a very disruptive effect.

After deforestation, do these landscapes become more susceptible to climate change?

Dr. V. G.

Yes – we are moving towards a system that does not have the same level of resilience and is not able to adjust to climate shocks. In south-east Asia, for example, we are talking about wet, carbon-rich ecosystems. They do not ignite, they do not burn. Once the trees are removed and the peat is drained for agriculture to make room for plantations, the peat15 becomes very dry and it becomes susceptible to fire.

And this releases carbon and adds to climate change

Dr. V.G.

Yes – peatlands are enormous stores of carbon. Fires occur every summer in south-east Asia. In 2015, during the last big El Niño event, there were huge fires across tracts of land in Sumatra and elsewhere. There is also carbon release just through drainage. When trees are cut down, channels are cut into the peat to drain the land, resulting in an upper meter or so of peat that is then exposed to oxygen, while it has not been exposed for thousands of years. Carbon and oxygen produce aerobic decomposition – when organic materials decompose in the presence of oxygen, and carbon rapidly disappears into the atmosphere as CO2.

How does deforestation affect the land?

Dr. V.G.

It can create artificial boundaries. The hydrology of peatland is such that, if a portion is drained, it will have knock-on effects many hundreds of meters or even kilometers away. This is not unknown to local land managers who will do their best to limit hydrology loss. The management of water in these landscapes is quite a challenge as water can be lost very quickly. Deforestation might also cause encroachment – for example, tigers moving out and seeking food elsewhere, leading to the additional challenge of human-species interaction.

“We are moving towards a system that does not have the same level of resilience and that is not able to adjust to climate shocks.”


More than forty percent of soil carbon is stored in the world’s peatlands.

Source: IUCN (2019)

Around the world, the scale of deforestation has been enormous. Do you see attitudes changing?

Dr. V.G.

The Amazon is being depleted at the rate of a football pitch of tropical forest every minute. This is very politically sensitive. In Brazil, some land users now feel they can deforest again because of the recent change of government. Elsewhere, in south-east Asia for example, there are moratoriums in place – ironically, some of the big landholders end up almost ‘policing’ the fragments of natural forest that remain. It is a very complex situation and tensions arise. For example If you build a road, for economic development so that a community can get greater access to markets, more people will come into the forest that the road cuts through; they may lay claim to the land through legal or illegal means with often little policing or resistance, and clear the forest for crops or other products. The challenge is really about people, their movement and livelihoods and balancing the needs for economic development with protection of the forest. And this crosses borders – commodities grown in tropical forests are part of international markets – with palm oil and paper, and so on.

What are the possible solutions? How do we protect these forests?

Dr. V.G.

There are efforts to reforest – that can be a solution. In Indonesia, after the 2015 fires, landholders were told to raise the water table in peatland to within forty centimeters of the surface. That provides an opportunity to go back to native tree species that do not grow as quickly, but that grow well in a high-water table environment. It is not easy to raise the water table, but it can be done by introducing dams and sluices and regulating flows through drainage canals. There are a lot of issues relating to this, but landholders are starting to realize that their long-term economic sustainability depends on not losing their peat.


Biodiversity & climate change


Dr. Diego Navarrete,

The Nature Conservancy (Colombia)

How seriously are governments taking deforestation?

Dr. Diego Navarrete

Countries have been taking action. The Paris Agreement commits them to reducing their emissions. In the case of Brazil and Colombia, that means correctly managing agriculture and forestry and coming up with alternatives to reduce deforestation. In Colombia, 62% of total emissions come from deforestation and traditional agriculture – basically, cattle ranching. For tropical countries, with natural forests, this is a big issue. The REDD+ program16 provides a framework for developing initiatives as well as monitoring and reporting progress. In Colombia, the government has been implementing laws and incentives to meet its climate commitments and is working with different sectors and there is now a carbon tax17. In Brazil, the context is far more challenging.

How delicate are these forest ecosystems?

Dr. D.N.

They are very interconnected. We have fragmented the forest, which has a negative impact on processes such as pollination and seed dispersal. When a forest is cut down, the bridges that connect the different ecosystems within the forest are taken out. Before deforestation, species used to move from the Andean forest to regions in the Amazon. Now, those bridges have been removed and species in the Andes have become isolated from those in the Amazon.

How resilient are species to this kind of change?

Dr. D.N

Some are more resilient than others. Birds, for example, can fly and find resources elsewhere – food, breeding partners, places to nest. But other species are not so fortunate. We often take a very ‘human’ point of view. We ask: is this species useful to me? The sloth is a great example. Sloths do not represent anything economically, but they are important in ensuring a stable ecosystem. All species – animals, plants, even human beings – have a role to play. In that respect, if one species is lost, the whole stability of the ecosystem starts to weaken.

How do we improve land management? Can we make it more sustainable?

Dr. D.N.

We know that, through deforestation, we release carbon. First, when people cut down and burn the forest. Then, over maybe twenty years, we have legacy fluxes as carbon is released more slowly. If we start to manage land sustainably we can reduce these emissions, even neutralize them altogether – that means moving to lower-intensity agriculture. In Colombia, a program has been developed to convert traditional cattle ranches – pastures where the soil is often degraded – into much more productive, healthier areas through planting trees and taking a more ‘silvopastoral’ approach, combining trees and grazing land. The result should be better carbon capture, improved biodiversity – and increased productivity.

“We are moving towards a system that does not have the same level of resilience and that is not able to adjust to climate shocks.”


Deforestation and forest degradation are responsible for approximately 15% of global greenhouse gas emissions.

Source: Forest Carbon Partnership Facility (2019)


Satellite data shows an 84% increase in the number of fires in Brazil’s Amazon rainforest.

Source: INPE (National Institute for Space Research, based on data for January- August 2019)

Is business getting involved in helping tackle deforestation?

Dr. D.N.

Some companies are involved – they are definitely interested in improving conditions. At TNC, for example, we have a Water Funds Initiative to improve water quality and availability. This initiative brings together the private sector, government, local communities and NGOs, and we work as a solid block. With work on degraded land, there will never be the same level of biodiversity as there is in a forest, even in an area which is managed sustainably. The first step is to stop cutting down the forest – then to concentrate on degraded areas where the soil and vegetation can be improved. With that, quite soon, biodiversity will improve.

14 Gigatonnes of equivalent carbon dioxide (a simplified way of expressing various greenhouse gas emissions in terms of the carbon dioxide that would have the same global warming effect).

15 Organic deposit which consists of semi-decomposed plant material mixed with varying amounts of mineral, or inorganic, matter (Source: IUCN, 2014).

16 REDD – Reduce Emissions from Deforestation & Forest Degradation – was first negotiated in 2005 under the auspices of the UN Framework Convention on Climate Change (UNFCCC). It is supported by the UN, World Bank and national governments.

17 Introduced in 2017, Colombia’s carbon tax is levied at $5 /tonne of CO2. Proceeds are used to finance conservation initiatives. Colombia also applies tax breaks in areas such as renewable energy (source: Conservation Finance Network).


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