How climate has changed the world

The Morrison Government’s attitude to our history is that it started with Captain Cook and then – as if transported by the Tardis or Dr Emmet. L. Brown’s DeLorean car – arrived at the era of John Howard, Ronald Reagan, Margaret Thatcher and Milton Friedman.

If it took the time to look beyond this narrow prism it might get some insights into how climate variations have influenced world history by felling empires; provoking civil wars and economic destruction; how science is helping us understand what happened in these episodes in history; and, how the climate emergency will have more profound and long-lasting impacts than any of those other past climate events.

There is ample evidence of these historic changes from antiquity through the Middle Ages and into the 19th and 20th centuries.

One of the most recent also illustrates how science can uncover how climate can spill over into broader historical events. A paper by J.L. McConnell and others, Extreme climate after massive eruption of Alaska’s Okmok volcano in 43 BCE and the effects on the late Roman Republic and Ptolemaic Kingdom, published this year in the Proceedings of the National Academy of Sciences of the USA (PNAS) is a good example.

The falls of the Roman Republic and Ptolemaic Kingdom and the creation of the Roman Empire are probably among the most significant political events in Western history. Now through the wonders of dateable ice core analysis of volcanic fallout, combined with climate proxies and contemporary sources, we can understand a lot more about why and how it happened and what the consequences were.

In the abstract McConnell and his co-authors say: “The assassination of Julius Caesar in 44 BCE triggered a power struggle that ultimately ended the Roman Republic and, eventually, the Ptolemaic Kingdom, leading to the rise of the Roman Empire.

“Climate proxies and written documents indicate that this struggle occurred during a period of unusually inclement weather, famine, and disease in the Mediterranean region; historians have previously speculated that a large volcanic eruption of unknown origin was the most likely cause.”

The authors then show that “using well-dated volcanic fallout records in six Arctic ice cores that one of the largest volcanic eruptions of the past 2,500 years occurred in early 43 BCE, with distinct geochemistry of tephra deposited during the event identifying the Okmok volcano in Alaska as the source. Climate proxy records show that 43 and 42 BCE were among the coldest years of recent millennia in the Northern Hemisphere at the start of one of the coldest decades.

“Earth system modelling suggests that radiative forcing from this massive, high-latitude eruption led to pronounced changes in hydroclimate, including seasonal temperatures in specific Mediterranean regions as much as 7 °C below normal during the 2 y period following the eruption and unusually wet conditions.

“While it is difficult to establish direct causal linkages to thinly documented historical events, the wet and very cold conditions from this massive eruption on the opposite side of Earth probably resulted in crop failures, famine, and disease, exacerbating social unrest and contributing to political realignments throughout the Mediterranean region at this critical juncture of Western civilization.”

Virgil’s lines – “And likewise, mourning Rome, with Caesar dead,/In dim rust-coloured haze he (the Sun) veiled his head” – may not be simply metaphorical but rather reflecting the reality of volcanic-induced climate change.

In a PNAS Commentary article on the research Clive Oppenheimer from the Cambridge Geography Department surveys other literature on volcanic climate impacts including John  Post’s book on the 1815 Tambora eruption and its links (combined with the economic aftermath of the Napoleonic Wars) with social, demographic and political change and the 20 odd works that have been published as “it emerged that an extraordinary archive of information on post global volcanism lies locked in the polar ice sheets.”

If residues in ice can help explain the rise of the Roman Empire they also help in explaining its demise. Bryan Ward-Perkins, an Oxford historian, in his The Fall of Rome and the end of Civilisation challenges the argument that the transition from the Romans to the Germanic tribes was largely peaceful. In fact the traces show that there was a dramatic fall off in industrial production around the period and the physical evidence of population density and building construction suggest the coming of the ‘Dark Ages’ was not mythical.

Geoffrey Parker, in Global Crisis: War, Climate Change and Catastrophe in the Seventeenth Century, has similarly convincingly linked the 17th century ‘Little Ice Age’ with global crises. Parker looks at scientific evidence concerning the climate conditions of the period; and, links it with first-hand accounts throughout the world of political, economic and social crises.

His account takes into account China, England, North and South America, Japan, the Russian empire and sub-Saharan Africa and encompasses revolutions, droughts, famines, invasions, wars and regicides (Charles I in this case plus a few royals, princes and lords in other parts of the world).

Longer and harsher winters, and cooler and wetter summers disrupted growing seasons, causing dearth, malnutrition, and disease, along with more deaths and fewer births. Some contemporaries estimated that one-third of the world died, and much of the surviving historical evidence supports their pessimism.

The work of McConnnell et al, Parker and others makes it clear that we face similar catastrophes – except that with the climate change it may not be transitory if we continue with the Trump and deniers approach or the magical Morrison thinking of meeting the Paris goals “in a canter”.

Oppenheimer says the McDonnell et al research “carries a message for our future.”

And while book blurbs are infrequently useful the one on Parker’s is apposite: “the contemporary implications of his study are equally important: are we at all prepared today for the catastrophes that climate change could bring tomorrow?”

In Australia, however, we are not prepared because our government is not listening to the messages. It is too busy paying hundreds of thousands of dollars to the usual suspects in the tax avoiding oil and gas industries to come up with industry policies which will result in stranded assets or end up like the Northern Ireland Government’s encouragement of DeLorean manufacturing.

Note: John Spitzer alerted the blog to the PNAS paper.