Recent surveys have indicated a 69% global reduction in the abundance of species between 1970 and 2018. In Latin America this figure is as high as 94% whilst freshwater species are down 83%. This biodiversity loss is due to a range of factors and includes agriculture, development, pollution, exploitation, population rise. Numerous authors have predicted that we could be facing a sixth mass extinction driven by anthropogenic factors such as climate change.
Biodiversity is also likely to be affected by climate change and this may occur in two ways; catastrophic weather events such as wildfires, storms and floods could lead to local extinctions and severe and sudden decreases of abundance whilst climate change is expected to affect the distribution and survival of many species. As temperatures rise, we are likely to see a twofold impact on biodiversity; the distribution and range of species is likely to shift and phenological responses, or seasonal response times, will also shift. In terms of the ranges of species it is expected that species will begin to migrate poleward, to higher elevations and to greater depths for marine ecosystems as they track their ecological niche during climate change. In Europe and the Northern Hemisphere this will mean a movement of species northwards and plants will flower much earlier than usual, for example.
Break-up of ecosystems
As we witness a northward shift in the distribution of species so the Southern edge of their range will also shift north, however, this change in the southern edge is likely to be at a different rate, slower than the shift to the north. Another factor of this is that plants will not migrate at the same rates as birds, invertebrates and mammals, indeed, differential rates of migration are expected to cause the fragmentation and break-up of ecosystems particularly where species new to an area are able to out-compete the indigenous species .
This phenomenon of invasive species is already observable; in the UK Himalayan Balsam and Japanese Knotweed form large swaths or banks of vegetation that are devoid of native species. The American signal crayfish has devastated native crayfish species across Europe and there are numerous other examples. The response to invasive species in the UK is to conserve our native species by physically removing invasives from the habitat, as a citizen scientist I spent many mornings trawling the Thames tributaries pulling Himalayan balsam, but new species can also be benign or beneficial.
Sixth mass extinction predictions
As species reach their ecological limits driven by the change in abiotic factors occurring due to climate change their survival will depend on their ability to colonise new areas. This process will inevitably result in new and potentially invasive species becoming established in sites where they were previously unknown. This classically Darwinian response, the survival of the fittest, will mean that many species will shift geographically as we have described. This raises the question of how we should manage these phenomena in order to both protect native flora and fauna whilst providing habitat for species migrating due to climate change. The change in conditions is likely to happen too quickly for many species to respond leading to predictions of a sixth mass extinction.
Net Gain policy mitigations
One of the measures that has the potential to mitigate for these issues is the Net Gain (NG) policy as outlined in the UK Environment Act 2021. Essentially, this involves the requirement for all developments including NSIP’s (Nationally Significant Infrastructure Projects) to demonstrate a 10% increase in biodiversity prior to planning consent being granted. This being accomplished with a NG report that details proposals for habitat offsetting that increase overall habitat by 10%. This land-use policy will have the effect of providing space for habitat desperately needed for the recovery and ultimately the survival of many species. There are a number of countries already implementing BNG (Biodiversity Net Gain) including France, Canada and Australia. The Lawton Review, also of the UK, called for a network of interconnected sites for nature creating habitat and corridors linking them. Implementing the NG process could well result in the aims of the Lawton Review being realised. NG may provide space to sustain biodiversity in a changing climate.
Turning the tide
We must find ways to help species withstand the warming climate. Supplying interconnected sites of varying habitat types is almost essential for species survival under the predicted conditions. To turn the tide on biodiversity loss a simple strategy of supplying land for habitat, via NG policy, could prove to be a significant factor.
The biodiversity crisis was the prime focus at the Rio Earth Summit spawning Biodiversity Action Plans across the globe. It seems now to be overshadowed by the climate crisis and CO2 management policies. To avoid a sixth mass extinction, caused by the actions of humankind, we as a global society need to act now to save our biodiversity. Species need habitat, habitat needs land.