Archive for the ‘climate effects’ Category

Biodiversity, extinction and climate change

February 19, 2011

The previous thread turned into a discussion on how climate change might affect biodiversity. It started with Jeff Id’s taunt:

A warmer world will produce more food, biodiversity and a nice place for people and critters to live. Polar bears might be mad, but life is hard.

Aftersome back and forth’s, with e.g. Dave H noting the apparent disconnect between a strong focus on uncertainty and such a strong statement about positive effects, ecologist Jeff Harvey chimed in:

high temperatures are not a pre-requisite for high biodiversity

He points out that an important factor for maintaining high genetic and species richness is

stability – that is, that conditions in a region are not altered frequently by some important extrinsic challenge, such as rapid local climatic changes. (…)

the current rate of warming threatens to seriously undermine the functioning of biomes and ecosystems through uneven effects on species within tightly interacting food webs. (…)

Our species has simplified the planet biologically through the combined effects of paving, ploughing, damming, dredging. logging. slashing and burning, mining, dousing in synthetic pesticides, biologically homogenizing (e.g. through invasive species), altering the chemical composition of the air and water, and through various other forms of pollution. We know that genetic diversity is being lost at rates unseen in 65 million years, and against this background we are challenging an already impoverished fauna and flora to respond to climate changes that are unprecedented in perhaps tens of thousands of years.

Jeff Id replies:

I think like so many tied up in the eco-sciences you have blended too many causes and effects together to attribute the micro-warming to anything damaging to the ecosystem. (…)

my point is that over the next hundred years of warm weather, it would certainly result in higher planetary biomass all other effects unconsidered. Higher biomass eventually results in higher diversity. Warm in general is good for the planet, if you do it slowly enough and not too much of it.

How fast and how much, we could argue all day.

I tried condensing Harvey’s points thus:

- Biodiversity depends more strongly on the rate of change of climate than on the actual climatic state (i.e. whether “warm” or “cold”).

- That is consistent both with evidence from the past and with theoretical considerations

- Biodiversity is already being stressed (by multiple anthopogenic stressors, of which climate change is one), and this stress is likely to increase as (the rate of) climate change will increase. (i.e. future projected biodiversity loss is much stronger than current biodiversity loss)

Of course, it’s a bit more cpmplicated than that, as Harvey aludes to in his reply. Later on he notes that

The IUCN (…) does not classify a species as being ‘formally’ extinct until it has not been recorded in the wild for at least 50 years.

And on the current rate of extionction:

We KNOW that between 10 and 40% of well-known species (vascular plants and vertebrates) are threatened with extinction.

This is an area that don’t know much about, so I don’t have much to add. It’s a very important aspect though, especially when taking into account that projected future (rates of) warming are much stronger than what we’ve seen so far. Not to mention that once a species is lost, it’s lost practically forever. I would think that the rate of species loss can be much greater than the maximum rate of new species development (or creation if you wish ;-).  

References on biodiversity, extinction and climate change:

Extinction risks from climate change

Coral decline threatens fish biodiversity

Papers on ecosystem response to past climate change

Kate at Climatesight on extinction and climate

Association between global temperature and biodiversity, origination and extinction in the fossile record

Recommended reading by Jeff Harvey


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