From Almuth Ernsting
Neil Fisher (5 March, p 32) suggests that most of the global warming projections of the Intergovernmental Panel on Climate Change are flawed because, he thinks, there must be negative feedbacks which will counter global warming (5 March, p 32). He believes that, without such negative feedbacks, the climate would not have been stable over thousands of years.
Climate history, unfortunately, gives us many examples of abrupt and catastrophic climate change. Some 13,000 years ago, global temperatures first dropped and, many centuries later, rose by well over 3 °C. In both cases the temperature change occurred within less than 50 years. Buried mangrove forests have been found under the Great Barrier Reef which suggest a 3-metre rise in sea levels in less than 30 years, following the end of the last ice age, at least in that region.
Longer ago, massive and abrupt global warming saw a rise of 8 °C in sea-surface temperatures during the early Eocene. The greatest extinction of all times, at the end of the Permian, coincided with a sudden massive rise in greenhouse gases.
The climate experienced since the last ice age has indeed been stable, but then greenhouse-gas levels, and probably the amount of radiation received by the Earth, have been fairly stable until recently. If we look further back, we find a climate that is quite stable within small parameters and prone to abrupt and catastrophic changes when pushed too far. Climate history gives the strongest warning that we must not push the system too far – and that we must keep greenhouse-gas levels under control.
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Aberdeen, UK
