After the publication of RSPB's new report on the impacts of climate change on wildlife, Dr Tom Oliver shares more detail on the ways that extreme weather events make up part of the picture.
Dr Tom Oliver, Associate Professor of Landscape and Ecology at University of Reading.
Detecting the impacts of extreme events using long term species monitoring data
Extreme weather and climate events
Many climate models (e.g. the set of international models used to develop climate projections for the latest IPCC5 report) predict an increase in the frequency of weather extremes. The recent IPCC5 report predicts that it is “virtually certain that there will be more frequent hot and fewer cold temperature extremes over most land areas on daily and seasonal timescales, as global mean surface temperature increases, and it is very likely that heat waves will occur with a higher frequency and longer duration.”1 If these temperature rises are not accompanied by increased precipitation then we will also get more droughts.
For example, a recent study that I led2 assessed projected changes in spring-summer aridity* for Central England from 17 climate models. We found that the extreme aridity that occurred in 1995 (the most extreme spring-summer drought in the historical record of 238 years) was projected to occur roughly every 6 years under even the lowest CO2 emissions scenario (IPCC RCP2.6 scenario). This increased, effectively to every year, under the most severe scenario (RCP 8.5). Current emission trajectories are putting us on track for the most severe scenario....
The impacts of extreme weather events
Extremes such as cold winters, drought (and associated wildfires), days of extreme heat and intense rainfall (with subsequent flooding) have the potential to disrupt species communities for long periods after the initial event has passed.
Recent research, however, has also shown how the impacts of extreme weather events on species populations can be mediated by the structure of the landscape in which they live. One reason for this is that microclimatic conditions can vary between locations. For example, the centres of large woodlands are much moister and research shows that mobile species like butterflies3 and crickets4 will move in and out of woodland as the weather changes. This is a form of ‘behavioural thermoregulation’ (think taking off your jumper when feeling hot and putting it back on when cold) that maintains the health of individuals. However, problems arise when suitable habitats are not available nearby, or when they are of very low quality. In these cases, individuals can suffer greater impacts during weather extremes, when individuals are unable to find shelter. The availability of high quality habitats during extreme weather can also ensure that food remains available for species. For example, for insects, the quality of host plants is very important and if plants dry out, as they may do in open exposed areas during a drought, then the insects will need to find alternative resources in wetter locations.
Examples of landscape structure moderating the effects of extreme events are becoming increasingly documented in the scientific literature, with examples in amphibians 5, butterflies 6, crickets4 and birds7, to name just a few.
What can we do to help species adapt?
The general conclusion is that where land use is more hostile to species, for example when there are large extents of intensive agriculture, then species will suffer greater impacts of extreme events. For example my recent study2 of six drought-sensitive butterfly species in the UK showed that, unless we improve the quality of landscapes for these butterflies (by reducing the fragmentation of semi-natural habitats), then there are likely to be widespread local extinctions under all climate change emissions scenarios.
We can therefore learn important lessons for adaptation to climate change. For example, following the same UK butterfly example, if habitat extent is increased, and the new habitat is created in a way that optimally reduces the total ‘edginess’ of existing semi-natural habitat patches, then the population persistence of these butterflies is improved. That said, to achieve a greater than 50% chance of population persistence right through to 2100 was projected to be possible only under a combination of both low emissions (RCP2.6) and semi-natural habitat restoration. This absolutely underlines that we need both climate change mitigation and adaptation.
In praise of long-term monitoring!
To understand these impacts (and the way they are mediated by landscape structure) requires long-term monitoring repeated across many locations. This can either be through paid surveyors or through trained volunteers. An excellent example is represented by the many bird-(http://www.ebcc.info/pecbm.html) and butterfly (http://www.bc-europe.eu/) monitoring schemes across Europe. In some countries, new schemes are underway to expand such standardised monitoring to other species groups (e.g. plants in the UK http://www.npms.org.uk/). These volunteer schemes represent excellent value for money for governments needing to understand and respond to climate change. They also have the added value of expanding understanding of the natural environment and the impacts of climate change among the general public. However, even these schemes will need some financial support for the co-ordination of volunteer action.
Climate change acts upon biodiversity in complex ways and in order to preserve biodiversity over coming decades we will need the best information available. Ideally such monitoring should encompass as many species groups as possible. Just like when piloting an aeroplane we would want a full range of information dials, to ensure that we are flying the safest course possible. In a similar way, species monitoring schemes allow us to assess the impacts of climate change in real time and to inform the design and effectiveness of necessary adaptation options. There is a large amount of uncertainty in both the impacts of extreme events and the best way to deal with them. Only with sufficient long term species monitoring will we have the information to make the best decisions to protect biodiversity for ourselves and for future generations.
*aridity was calculated using an index that combines daily temperature and precipitation data between April-September
The large skipper Ochlodes Sylvanus, a species identified as drought sensitive in our study2. Photo credit: Tim Melling.
Observed annual spring-summer aridity* in the UK (black points) and projected aridity under different greenhouse gas emissions scenarios (coloured lines) reproduced from Oliver et al.2. The horizontal dashed line shows the highest aridity on record in the year 1995.
References
1 IPCC, Climate Change 2014 Synthesis Report Summary for Policymakers. (2014).
2 Oliver, T.H. et al., Interacting effects of climate change and habitat fragmentation on drought-sensitive butterflies. Nat. Clim. Chng. 5, 941 (2015).
3 Suggitt, A.J. et al., Habitat associations of species show consistent but weak responses to climate. Biol. Lett., http://dx.doi.org/10.1098/rsbl.2012.0112 (2012).
4 Kindvall, O., The impact of extreme weather on habitat preference and survival in a metapopulation of the bush cricket Metrioptera bicolor in Sweden. Biol. Cons. 73, 51 (1995).
5 Piha, H., Luoto, M., Piha, M., and Merilä, J., Anuran abundance and persistence in agricultural landscapes during a climatic extreme. Glob. Ch. Biol. 13, 300 (2007).
6 Oliver, T.H., Brereton, T., and Roy, D.B., Population resilience to an extreme drought is influenced by habitat area and fragmentation in the local landscape. Ecography 36, 579 (2013).
7 Newson, S. et al., Can site and landscape scale attributes buffer bird populations against extreme weather events and facilitate recovery? Ecography 37, 872 (2014).
Matt Williams, Assistant Warden, RSPB Snape.