Our home in space

some remarks on global heating and ocean acidity

Guy Ottewell

Shifting zones and seasons

Climatic zones are shifting: poleward (northward in the northern hemisphere) and up the slopes of mountains. Average annual temperatures are moving northward (in the northern hemisphere) at a rate of 4 kilometers a year — 20 times faster than temperatures shifted during the onset and retreat of the last Ice Age.
        In early 2010 it was discovered that some of the sea lions of the Galápagos islands (near the equator) had for the first time moved away, 900 miles southeast to an island off the coast of Peru. The average temperature of the water around the Galápagos had risen over ten years from 17 C to 23 C, so the sea lions had moved to the nearest environment they could find where the water was at the temperature they had been used to.
        Species from continental Europe are moving north. There is a long list of these species that have recently appeared for the first time in Britain, some now as far north as Iceland: for instance damselfly and butterfly species, hummingbird hawk moth, violet carpenter bee, brown-banded carder bee, tree bumblebee, little egret, cattle egret, purple heron, and many so unfamiliar that they do not have English names. The spread of Asian hornets (which massacre honeybees) north from France to England will probably be hastened by warmer temperatures.
        Populations of British seabirds have declined because they rely on sand eels, which have moved north out of British waters. According to the Royal Society for the Protection of Birds, “Warming of the sea by just one degree Celsius allows warm water plankton to move in and replace the more nutritious cold water plankton that provide food for the sprats and sandeels that seabirds need.”
        When I was gardening in South Carolina, I learned that the growing season had become longer than was mentioned in books: the dates of last frost in the spring were earlier, and first frost in the fall later, and this kept becoming more so in my experience. It was not yet recognized that this was part of a general phenomenon called global warming. In Britain, according to experts at the Royal Botanical Gardens in Kew, the dates in spring when plants start to flower have over the past 30 years been getting dramatically earlier (with exceptions after cold winters such as that of 2009/2010). This might seem fine, except that it points toward a possible future in which Britain has the climate of the Mediterranean and South Carolina that of Florida, while the Mediterranean and Florida become desertic.
        Regions with hotter and drier climates are becoming larger. These include the regions with Mediterranean-type climate (cool moist winters, warm dry summers) and deserts like the Sahara.
        Regions of grassland in many parts of the world are being invaded by woody shrubs, which are favored when there is more carbon dioxide in the air. This is already having a great effect on the livelihood of people dependent on rangelands, including in the U.S.
        In 1944 the U.S. navy made a set of detailed photos of northern Alaska. The rediscovery of these photos, and their comparison with modern satellite images, has shown that the tundra all across Alaska, also Siberia and Canada, is becoming covered by shrubs. The zone of boreal forest south of it is advancing northward, but is at the same time “browning” and dying, progressively from its southern edge. This is because of increased warmth accompanied by drying; the warmth also leads to increased insect infestations and increased frequency and size of forest fires.
        In Britain, spring is arriving more than two weeks earlier than in the 1980s, 3 weeks earlier than in the 1950s might seem pleasant, but migrant birds arriving at their usual times 'find the food their young depend on has already bred/pupated/hatched/or gone to ground; and plants flower before their pollinators are on the wing.
        In the Arctic Ocean every summer there is a blooming of phytoplankton, which are the base of the food chain. This blooming used to peak in September, but now because of the shrinking of the ice cover it has moved as much as 50 days earlier, to early July. This was discovered in satellite data from 1997 to 2009 (and published in the journal Global Change Biology in 2011). Biologists fer that such a massive change in such a short time could unravel the region's ecosystem and “lead to crashes of the food web.