Climate optimist or pessimist?

I love questions after a talk. It gives me a sense of whether I got my points across and how engaged the audience was during the talk. However, a question from the audience after a recent seminar caught me a bit off guard - "So, you sound like an optimist when it comes to climate change. Why?"

photo by @jot_au

In many ways, I'm an optimist in life -- with all the ups and downs in science, I'd be depressed and probably give up otherwise -- but when it comes to the outcomes of climate change, I'd like to think I'm objective. I believe its pretty clear that there will be winners and losers. Some of the losers will likely go extinct. My bigger concern is understanding who the winners and losers will be, WHY, and what effects will that have on ecosystem function.

Obviously, we can't do experiments on every species in the world, so understanding WHY (the mechanism for persistence or frailty) is essential for predicting the fate of others. I focus on plasticity during development as a way for species to rapidly (within an individual's lifetime... often within days) respond to environmental change. I chose this because it is intimately tied to dispersal and I think it gets far less attention than other mechanisms such as range expansion, change in reproductive timing, and behavior, but could be equally important. Unfortunately for the purple sea urchin, it appears that its changes in development in response to food will NOT help it adapt to climate driven mismatches between when food is available and when larvae in the water column (Adams et al 2011, Nature Communications). 

All of the mechanisms mentioned above, with the exception of range expansion, rely on plasticity (alteration of form, function, or behavior) in one way or another. Range expansion could simply be due to increased survival at the range limits as temperatures become more optimal or tolerable for a given species.

AP Photo/Butterfly Conservation, Keith Warmington

New findings published today in Science show that range expansion can also be facilitated by plasticity. The brown argus butterfly in the UK has rapidly expanded its range to the north not just because temperatures warmed. Key to the expansion was utilizing another host plant - plasticity. During cool periods, the new host plant was not as well suited and resulted in higher caterpillar mortality. However, warmer temperatures have now made this plant a better host, boosting population growth and expanding the butterfly's range.

Many animals have these sorts of complex interactions with other species - predator-prey, parasite-host, symbiosis, etc - that can either hinder or propel response to climate change. Taking an opposing scenario for the argus butterfly - if there hadn't been an additional host plant, the butterfly's range would be confined to the spread of the range of the single host plant, even though the butterfly alone could physically tolerate more northern habitat. And for the more pessimistic view, although the butterfly's range is expanding rapidly to the north, it does not appear to be keeping up with habitat loss in the south. So this butterfly may be a "Global Change Winner" in the UK, it may be a loser overall.

Still, the story highlights the need to include multiple species interactions in our mind when considering climate change. Temperature and pH (ocean acidification) tolerances alone are not sufficient.

Its a complex story. The only thing I'm clear about is that there will be change.