Spring seems capricious. Warm breezes soften ice on a local pond, then storms bury it in snow again; one day there are tiny spikes of green grass and the next there’s only endless gray slush. But if we look at temperature records for any region over a span of time, the profoundly capricious variation we see suggests that wholly unpredictable change is both normal and natural.

Graph of average temperatures over the last million years (scale in thousands), from B. Saltzmann, Dynamic Paleoclimatology: Generalized Theory of Global Climate Change (Academic Press 2002).

This does not mean, as some suggest, that we should be complacent about the unprecedented rate of environmental change the world faces now. Instead, it calls us to reconsider our practice of designing structures, food plant genomes, and land

or water use patterns to precisely fit today’s “normal” conditions -- which are clearly only transitory. Just how transitory depends on how well we’re able to slow the human-induced changes we’re adding into

the system. Reducing carbon emissions slows global warming and so buys us much-needed time to figure out how to live with enough “give” in our systems to adapt to natural change when (not if) it comes. But sooner or later, to survive, we will have to learn that we can’t assume it’s natural or normal for present conditions to stay the same forever, and that it’s dangerous to design our cities, water supplies, and crops as if they will.