We all know that weather is not the same as climate, but it is surprising how our perceptions of global warming vary according to what we see outside our window. In the UK for example, last year’s washed-out summer took the focus off global climate warming in many people’s minds – maybe the current heatwave will change that. But regardless of what may be happening in our back yards, the long term trend is one of warming - which it has done globally by an average of 0.74C˚ over the past century.
As the climate warms up, animals and plants have three main alternatives: they can either move to track the temperature, stay put and adapt to the warming, or die. Responding to variation in climate is not a new phenomenon for species – after all, many species responded to climate warming after the last ice ages.
Two recent papers have examined the ability of species to adapt to climate warming in situ by staying put. The first study examines the evolution of more than 500 animal species over millions of years. The second study focuses on a population of a single bird species at a site in southern England that has been studied intensively since the 1960s. They come to very different conclusions about the prospects for the species under future climate change.
The first study examines how quickly about 500 vertebrate species have evolved in the past, and how quickly they need to evolve in future if they are to stay put as the climate warms. The authors come to the conclusion that their studied species will need to evolve at least 10,000 times faster than they have in the past to cope with the degree of climate warming that is projected in the next 100 years. Therefore, they conclude that species moving to track warming is the only option that these animals will have to avoid extinction.
The second study investigates how flexible great tit birds can be over the timing of when they lay their eggs. Many animals and plants have been shown to alter the timing of spring events such as flowering, egg laying, or migration when spring is warmer. Synchronising activities to coincide with spring is important for the success of many species. In the case of great tits, they need to synchronise their breeding with the availability of caterpillars, which they use to feed their chicks. By studying these birds over the past 50 years and their potential for local adaptation, the authors conclude that these birds have an inbuilt capacity to cope with future projected climate changes, assuming that this plasticity can keep track with the rate of change.
So why this apparent disagreement from the two studies? The results from the great tits imply there is sufficient capacity within the population to cope with future changes - although the authors acknowledge that a similar study in the Netherlands was more pessimistic. This contrasts with the first study, which suggests that observed rates of past evolution have been way slower than those needed in future, such that species will go extinct unless they adapt.
Some of the differences may be due to the different scales of study. There is a big difference between large scale “macroclimate” and small scale “microclimate” assessments of species behaviour. Most studies which analyse macroclimates do not take account of local variation in microclimate, or the adaptation of species to local conditions. They neglect to consider that species may be able to take advantage of local variation in slope and aspect if climate conditions become unsuitable. Even if this doesn’t help long-term, it may buy species some time.
However, beyond the small-scale adaptation shown by great tits, there is little evidence that suggests that species can evolve at the rate of projected climate change. There is, however, a large body of empirical scientific evidence showing how ranges of animals and plants are moving to track climate changes.
Research from my lab shows that most species are shifting uphill and towards higher latitudes; we also have data showing butterflies disappearing from sites as they get too warm - hence we currently have little evidence for adaptation.
So, in the words of The Clash, these species have already made up their mind about “should I stay or should I go".