The Big Picture - Climate Change and Extinctions

One of the most important messages of this blog has been to get across the sheer variety of ways that climate change influences the lives of species and their associations within and beyond the ecosystem. This influence has taken the form of many different ecosystem responses, such as rapid range shifts, changing phenologies, increased invasions, genetic polarisation and much more. Last week we saw how all of these effects come together to erode ecosystem resilience, and this week, as we come towards the end of our blogging journey, I would like to discuss how they are pushing species on a global scale towards extinction.

As Bellard et al.(2012) state (and we have seen), climate change is expected to affect all levels of our planet’s biodiversity. This ranges from biota at an organism level, all the way up to the biome, and will affect not just individuals, but species, their populations, ecological networks and ecosystems as a whole. At the small-scale level, as we have seen over the past couple of months, climate change causes phenological desynchronization (such as with the Pied Flycatcher, as discussed in an early blog), can damage genetic diversity (as shown by Cobben et al. 2012 in a previous blog on the unforeseen consequences of range shifts) and can make ecosystems more susceptible to invasions by non-native species. At the community scale, we have seen that the complex “web of interactions” can become desynchronised or entirely broken, through examples such as that of benthic plankton communities. At yet a higher level, climate change also threatens to cause ecosystem and even biome collapse (as discussed last week). In fact, the Millennium Ecosystem Assessment predicts biome shifts for 5 to 20% of Earth’s terrestrial systems (Sala et al. 2005; chapter 10).

We have also seen that species, populations and ecosystems have a variety of mechanisms with which to deal with these changes. When looked at together, and as Bellard et al.(2012) state, these responses can be largely grouped into three categories. These include spatial responses, such as range shifts in both latitude and elevation, temporal shifts, such as phenological plasticity, and finally “self” shifts, which Bellard et al. (2012) describe as species or communities adapting themselves to new conditions through a process of microevolution, whereby species genetically adapt by way of new mutations or selection of already existing, and better adapted, genotypes.  Whilst this provides affected species and ecosystems a variety of methods by which to “get out of dodge”, ecologists across the board are finding that many of these responses are entirely inadequate to counter the rapidity and scale of modern climate change. Not only this, but unlike in previous episodes of climate change, that were arguably well weathered by Earth’s biological community, species are now finding themselves having to cope with additional threats such as land-use change and pollution, which act somewhat in tandem with climate change to really drive species towards the brink (Bellard et al 2012).

When species do find themselves unable to cope with the challenges of climate change, the harsh reality is that they go extinct. This can happen both at local and global levels, with local extinctions understandably being significantly more common. Understanding the possible trends of these extinctions, alongside biodiversity change is incredibly important both for understanding of the issues and the construction of efficient, focused and relevant responses (Bellard et al.2012). Many ecologists, then, have strived to understand the potential future patterns of these extinctions, and numerous studies exist that project these future changes.

One of the most referenced comes from Thomas et al. (2004), mentioned in our first blog, who famously estimated that 15-37% of all of Planet Earth's species could be committed to extinction by 2050 under more intermediate models of climate warming. A similar meta-study, published in 2011 by Maclean and Wilson, estimated relatively similar rates of 12.6% of plants committed to extinction, 9.4% of invertebrates and 17.7% of vertebrates. A range of studies that investigate more specific extinction projections also exist. Koh et al. (2004) for instance conducted a study of 9,650 interspecific relations and found that an estimated 6,300 species could become extinct following the extinction of their associated species. Sekercioglu et al. (2008) on the other hand investigated extinction risks for terrestrial avian species (as birds are deemed to be especially sensitive to changing climates), finding that up to 30% could become extinct by 2100. Moreover, Malcolm et al. (2006) found that endemic species were also at significant risk from climate change and that losses of 39-43% might be realised in worst-case scenarios, translating to an absolute loss of 56,000 endemic plants and 3,700 vertebrates.

Similar predictions also exist in relation to biodiversity loss. Alkemade et al. (2009) for instance found that we could face decreases of between 11 and 17% of mean species abundance, and the International Union for the Conservation of Nature forecasted that globally, 35% of birds, 71% of warm-water corals and 52% of amphibians would be especially at risk of degradation (Foden  et al. 2008).

There are an incredible range of studies then that attempt to project and quantify the future for species across the globe. However, as Urban(2015) states in his very recent study from May, these current predictions vary hugely depending on the assumptions, method, focus and thresholds of each study. Whilst other meta-studies circumvent this problem, such as those aforementioned, it makes it hard to build up a large and reliable global picture. Urban (2015) hence conducted a meta-analysis of 131 multi-species predictions, finding that 7.9% of species globally can be expected to become extinct due to climate change. Specifically, this projection is 5.2% for 2^oC warming (that many experts (and myself included) no longer see as a feasible target), 8.5% for 3^oC warming and a staggering 16%, or as Urban (2015) puts it, 1 in 6 species, if we continue business-as-usual.

A graph from Urban (2015) that details the predicted extinction risks associated with varying global temperature rise

If the past three months’ worth of blogs hasn’t made it clear, then hopefully after reading today’s blog the sheer scale of destruction caused by climate change will finally have hit home. These projections show that the natural world is currently on the path to becoming completely devastated. Even the lowest, most conservative estimates such as Urban’s (2015) 5.2% or Thomas et al.’s (2004) 9% would be absolutely devastating for our planet’s ecology, causing widespread ecosystem and biome collapse and resulting in the permanent loss of many wonderful and unique species.

Throughout this blog we have examined closely the direct effects of climate change on our flora and fauna. Now, to round it off, we start looking at the future. It's not a bright one. After conducting so much research and learning so much about the whole sorry state of affairs, it looks like climate change is one of the biggest threats to our fauna and flora for millennia. 

In the last blog of the series, which should be coming out tomorrow, I would like to look to the future, and briefly discuss what needs to be done before bringing this project to a close. As much as I’d like this blog to have a happy ending however, already it is becoming too late for numerous species, and however hard we do try to change our ways and save species, the time is well past that damage can be entirely prevented.