Human effect on climate change

IN his recent letter, Denis Hough poses the question whether human action was contributing to global warming 1,200 years ago? The answer is yes, but not to the same extent as in the years since the industrial revolution.

The ‘early anthropocence’ hypothesis of the renowned palaeoclimatologist William F. Ruddiman argues that humaninduced changes in greenhouse gases did not begin in the 18th century with the advent of coalburning factories and power plants of the industrial era.

Rather, they date back to 7,0008,000 years ago and were triggered by the farming activities of our early agrarian ancestors, and especially by large scale deforestation and rice cultivation which increased carbon dioxide and methane emissions, respectively, particularly over the past 3,000 years.

Of course, carbon dioxide and methane concentrations in the atmosphere have risen much more dramatically in the period between 1750 and 2022, from 227 ppm and 719 ppb to over 420 ppm and over 1915 ppb, respectively, but it is believed the pre-industrial increases in greenhouse gases due to agriculture may have been sufficient to prevent an incipient ice age developing earlier in the Holocene (post-glacial) epoch.

In addition, contrary to what Mr Hough seems to be somewhat mischievously implying, the incidence of serious flooding in prehistorical, historical and modern times are not all the result of the burning of fossil fuels.

Rather, the significant and accelerating effects of anthropogenic global warming has exacerbated such events and is very likely to make them more frequent and more extreme in the future.

Professor Bruce Webb

Exeter, Devon