I promised to post something on the effects of climate change on plants and animals, and in particular the article you linked reporting on climate change and extinctions. There are many estimates out there that a third or more of species might be committed to extinction by 2050. Some of these climate-related extinctions are already occurring. The way these estimates are made is by basically taking all recordings of where the current species are located and looking at the average climates that characterize these zones. These climate envelopes are assumed to constrain where a species can live sustainably. There are weaknesses to the approach because it doesn’t account for biotic factors (e.g. competitors, parasites etc) but it does a fairly good job of delineating where a given species can potentially survive.
Most of the people on this board probably reside in climate-controlled environments. For the time being, climate change means using more air conditioning and less heating. We get into trouble when major heat events hit areas that never used to need air conditioning, Europe in 2003 where as many as 70,000 people died from the event, or Russia in 2010 where a combination of the heat and smoke (many wildfires) killed 56,000 come to mind. Barring these extreme events though, we can safely shelter in our homes and weather the weather, so to speak.
Outside, however, the rest of nature has to just deal with whatever comes. Species are found where they are because they can survive what the elements dish out the majority of the time. Storms, droughts, floods and what not may cause high levels of local mortality but as long as there is sufficient time between such event the populations will recover. However, if conditions change sufficiently in either extent or frequency, then they may be in jeopardy. Should such conditions exist over much of their range then they could even be at risk of extinction.
In short, ecosystems are the result of long periods of relative climate stability that has allowed various species to interact and develop mutual relations that allow sustainable existence of populations. The whole process is dynamic with changes from year to year (kind of like the weather) but on average you know what to expect.
Climate change is a game changer. Ecosystems and individuals are designed to deal well with a fair amount of short term stress and bounce back. Climate change, however, is chronic stress. It is not surprising (at least to me) that the authors of the study you cited didn’t find a direct linkage between direct heat stress and extinction. Few of us die directly from chronic stress, it is all of the associated problems, reduced immune response, attention etc that are likely to get us killed. The same is likely true in all natural systems.
Now I am going out on a limb here with the rest of this and saying what I think (not what I can necessarily prove (yet). The ecosystems that we know are the product of 10,000 years of relatively stable climate just as much as our agricultural practices are. What we think of as natural associations weren’t always arranged in this way. Changing weather acts on individuals, changing climate acts on species. What this means in practice is that as climate change stress increases, the various species in any ecosystem will feel various amounts of stress and be nudged in one direction or another.
Periods of relatively slow climate change allow this reshuffling to proceed somewhat gracefully with migrations to new suitable habitats. As the rate of change increases, though, more and more species get lost in the shuffle. Either they can’t move fast enough (think redwoods) or something they rely on (pollinators perhaps) doesn’t show up on time, or the habitat doesn’t provide shelter, predators overwhelm them, competitors don’t let them in etc and their populations drop. Smaller populations and greater levels of stress are recipes for reduced production (offspring) and extinction.
One of the things that occupies my thoughts these days is trying to understand how this is going to play out across landscapes. We know where things are now and we know here they might want to be at some point in the future. However, all of the interesting (terrifying) stuff happens in the middle. At what point do the ‘natural ecosystems’ that we know start to dissaggregate or just shatter? Is this what we are seeing with the massive insect outbreaks in forests across western North America and other parts of the world? Do we try to manage natural ecosystems to remain what they currently are while knowing they are less and less suited to their environment or do we just stand back and let nature sort itself out extinctions and all? Perhaps we try to save species by trying to build our own ecosystems? That didn’t work out so well in Biosphere 2 and we’ve proven ourselves poor at predicting what the addition of new species to an area will do (Aussies can chime in on this point!). What to do? An ethical and logistical quagmire awaits us.
Neither this climate nor the eventual one we end up with are the problem, it’s trying to navigate between here and there that is going to be the crucible for all species (us included). I really don’t think that anyone (myself and the rest of the scientific community included) really understand the magnitude of what we have done. That said, I am a bit of an optimist where species are concerned. I don’t doubt that there will be many extinctions but I think that many species ill prove more resilient than we expect. At least I hope so.