J. L. BELL is a Massachusetts writer who specializes in (among other things) the start of the American Revolution in and around Boston. He is particularly interested in the experiences of children in 1765-75. He has published scholarly papers and popular articles for both children and adults. He was consultant for an episode of History Detectives, and contributed to a display at Minute Man National Historic Park.

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Thursday, August 14, 2008

Using Ships’ Logs to Study Climate Change

Guy Curtis at the British Redcoat alerted me to a British news story about scientists using Royal Navy ships’ logs from the seventeenth and eighteenth centuries to produce evidence about global climate. The first and fullest account appeared in the Sunday Times on 3 August: “Captains’ logs yield climate clues: Records kept by Nelson and Cook are shedding light on climate change.”

[Admiral Nelson, Captain Cook, and “Britain’s great seafaring tradition” all in the first lines! Too bad the research doesn’t go back to Sir Francis Drake, or the paper could have invoked every iconic cliché of British sail.]

Scientists examined those logs to see if the weather notes of British mariners were systematic enough to be useful as data. I would have been skeptical. The best British meteorological instruments of the 1700s—those made by the Hauksbee family in London—have been found to vary by as much as 10%. And most of the weather notes I see in diaries are subjective descriptions, not numerical measurements. Indeed, the Times states:

Most of these earlier documents contain verbal descriptions of weather rather than numerical data, because ships lacked the instruments to take numerical readings. However, [Sunderland University geography professor Dennis] Wheeler and his colleagues found early Royal Navy officers recorded weather in consistent language.

“It means we can deduce numerical values for wind strength and direction, temperature and rainfall,” he said.
Wheeler told the B.B.C., “You find lots of ships sailing in convoy, and they all record the same thing.” I wish the articles offered examples of that common terminology, but I trust that it’s there.

Crude as this method might be, it seems solid enough to work for what Wheeler has studied in the logs so far: reports of big storms. He found wide variability in storm patterns, including, for example, “a surge in the frequency of summer storms over Britain in the 1680s and 1690s.” That casts doubt on the notion that storm patterns which seem unusual today must be the result of new conditions. Nothing’s really unprecedented, Wheeler’s findings suggest.

That touches on one of the debates within climatology today: whether global, human-produced climate change (which most scientists agree is occurring) is producing more big storms or other changes in severe weather (where scientists are split, with many doubtful). I suspect that laypeople are even more prone than climatologists to see “global warming” behind such storms as Hurricane Katrina; humans want to believe that big effects have understandable causes.

The Times article goes on to state:
Wheeler makes clear he has no doubts about modern human-induced climate change. He said: “Global warming is a reality, but what our data shows is that climate science is complex and that it is wrong to take particular events and link them to CO2 emissions. These records will give us a much clearer picture of what is really happening.”
The Telegraph, which leans solidly Conservative, summarized this article the following day, using the headline: “Lord Nelson and Captain Cook’s shiplogs question climate change theories: The ships’ logs of great maritime figures such as Lord Nelson and Captain Cook have cast new light on climate change by suggesting that global warming may not be an entirely man-made phenomenon.” That’s obviously trying to justify skepticism about how much human activity is changing the climate, and its article produced a flurry of predictable activity on warming-denial websites. Nevertheless, even the Telegraph included Wheeler’s quote above at the very end of its article.

Unlike in the U.S. of A., where well-funded pundits and a politicized minority protests most remarks about the facts and consequences of global warming, British society almost wholly agrees that we’re in a period of human-caused climate change. This summer I visited Bodiam Castle, and the signage outside its café says straight out that the land you’re standing on will be flooded in a few decades. So enjoy your cream tea while you can!


Steven Wyder said...

Interesting post J.L. Is it true that Ben Franklin took temperature readings at various depths to chart the gulf stream on his trips across the Atlantic?

Were those measurements recorded and kept? It would be interesting to compare those to current readings as well.

I seem to remember reading something about Franklin being credited for charting the gulfstream. Or did Franklin know about the gulfstream, then decided to try and chart it?

J. L. Bell said...

Franklin and his cousin, a sea captain named Timothy Folger, were the first people to publish on the Gulf Stream, with a map even shown here.

As I understand it (all from a paper I heard a few years back), by that time most transatlantic navigators probably knew about the useful current, but they hadn’t told the general public.

If global warming or anything else changes the gulf stream, then Britain will see much bigger changes than rising sea levels. The islands are at the latitude of Newfoundland, but have a more temperate climate thanks to the warm water flowing from the Caribbean. Take that away, and it's Denmark.