Anyone who has followed the climate change issue in the last 30 years knows that official forecasts provided by the Intergovernmental Panel on Climate Change (IPCC) are quickly upended by developments and have often been obsolete before they were issued.
The latest report from the IPCC is the first, however, to abandon the measured tone of its previous ones and foretell what it considers a climate catastrophe for human civilization unless the world makes an abrupt U-turn and begins dramatic reductions in greenhouse gas emissions almost immediately.
And yet, even this forecast is probably too conservative in its pronouncements. That’s according to Michael Mann, a climate researcher whose famous “hockey stick” graph has been central to understanding the rise in global temperatures and has been replicated again and again using other measures of historical worldwide temperatures.
What is little understood by the public is that humans have been underestimating the pace and impact of climate change since Swedish chemist Svante Arrhenius first suggested in 1896 that the globe was warming due to emissions of carbon dioxide.
Which brings me to a broader point: The public tends to hear most often about the median values or middle-of-the road scenarios in any forecast, sometimes called the reference case. (Very little emphasis is put on the range of possibilities. For example, the IPCC in 2000 forecast that global average temperature could be 1.4 to 5.8 degrees Centigrade higher than the 1990 level by 2100.)
Today, we find ourselves fretting that going beyond a 1.5-degree increase from pre-industrial times will spell catastrophe involving global agriculture, severe weather, sea-level rise, and disease epidemics. Previously, 2 degrees was thought to be the threshold for severe irretrievable consequences resulting from climate change.
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