Two degrees don't make a whole lot of difference to a sunbather on the beach, but they make one helluva difference to plant and animal life. We can debate the nuances of climate change science all we want, but the fact is that farmers in many regions of the globe are already feeling the pinch - from French vintners finding that their Bordeaux wines are migrating to cooler slopes, to South African farmers experiencing shifts in microclimates affecting their rooibos tea crops and Kenyans chasing their coffee up the mountains.
The Climate Action Network is demanding that the Bali conference discuss emission reductions by Annex 1 countries at a level sufficient to keep global warming to below 2 degrees. Why 2 degrees? It's a number that's stuck in the public consciousness since some of the earlier climate models were published, and the latest IPCC AR4 report, released last month, says:
There is medium confidence that approximately 20-30% of species assessed so far are likely to be at increased risk of extinction if increases in global average warming exceed 1.5-2.5oC (relative to 1980-1999). As global average temperature increase exceeds about 3.5oC, model projections suggest significant extinctions (40-70% of species assessed) around the globe.
It is sobering to note that 2 degrees of warming is a conservative estimate based on the IPCC's presentation of modelled climate change. Of six different scenarios presented in the latest report, all but one predict more than 2 degrees of warming by the end of this century. Along with the warming comes drought, flooding, pestilence and plague. In short: unpredictability.
Plant species also face extinction, and plant and animal life are obviously intertwined. The full implications of this scenario are impossible to predict, but this description of resilience from biodiversity by Thomas Linders hints at the problem:
Diversity (the number of species within a habitat, such as a wetland) is often considered a measure of ecosystem resilience (the ability of the system to accept disturbances): as the number of species increases, so does the complexity of the interactions of the different species with each other and with their environment; the greater the number of interactions, the more resilient the system is as a whole and the broader its capacity to adapt to change.
Humans are just one species among many, and are just as dependent on life support systems as any other. We need uncontaminated air, water and food; a healthy habitat with room to grow, and manageable levels of stress. And we are rapidly depleting all of these resources, not only through climate change, but also through many other processes that support modern life.
Much of what we do deliberately reduces diversity: tending weed-free suburban lawns and single-crop farms; clearing natural forests for cash crops; spraying pesticides that destroy organisms in the soil; breeding animals for specialisms like more milk or better meat; keeping birds and bugs away from fruit crops. We want uniformity, efficiency, productivity. Homogenised life.
Like rabbits in a cage, we are running out of options. Human resourcefulness might extend our ability to live in suboptimal conditions. Or not. A mathematician friend of mine recently pointed out that models of population growth and decline often show catastrophic decline in the face of resource stresses. Are we any different?
Enjoy your last two degrees. The ride might get a little rough from here.
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