Understanding climate change

Dr Sam Willis

Understanding the scope and speed of climate change is a formidable problem for modern climate scientists. One way they approach this is to use historical observations of climate to generate computer models of the global climate system. Such models are essential for the prediction of future climate change and the need for them is now particularly acute because of concerns about the speed of global warming: climate scientists need as much data as possible about past climate, and they need it now.
Much work has been done on historical climate data from terrestrial sources, such as the observatories at Greenwich, Edinburgh and Kew, the archives of National Meteorological Services, private institutions and individuals who kept climate data for their own research. Historical marine data has also been used extensively. However, the more data that goes into the models the better the results. Recently it has become evident that ships’ logs could be an excellent source for that data.
Hundreds of thousands of these log books survive, the vast majority of them in British archives. Watch officers of merchant ships, warships, submarines, whaling ships, exploration ships, survey ships and passenger ships, worldwide, recorded climatic observations, locations and dates in their ship’s log books. The most rigorous did so every two hours. Some even recorded instrumental air pressure and sea temperature.
The value of these sources for climate scientists, however, lies not only in the sheer quantity of this material, but also in the fact that the observations were made at sea. More than 75% of the world’s surface is covered by ocean; it is one of the defining characteristics of the earth as a planet. The quality of observations made at sea moreover, is necessarily more ‘pure’ than those made on land. There are no mountain ranges to create wind systems of their own, nor are there cities to increase temperature or create smog. Land-bound the majority of us may be, but it is to the sea we must turn to understand this aspect of our planet.
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Captains’ logs yield climate clues
By far the largest of the collections of log books is that of the Royal Navy, held at the National Archives in Kew. The pioneering scientist and Royal Naval Hydrographer Francis Beaufort was perhaps the first to acknowledge their potential for the study of the climate. "There are at present", he wrote "1000 King’s vessels employed. From each of them there are from two to eight log books deposited every year in the Navy office; those log books give the wind and weather every hour…what better data could a patient meteorological philosopher desire?".
These books survive in stunning condition, the earliest bound in calfskin and all of them beautifully conserved. Necessarily, some reveal the expected wear of life on a warship. Occasionally the handwriting scrawls as the ship is jolted by a wave; some have suffered from damp or have even survived a drenching. Others are stained with ink, wine or blood. Some are barely legible while others are written by the most expressive and cursive script. In amongst this chaos, above or alongside comments on the most significant events of that day, the climatic observations are ever present, a steady stream of knowledge that reaches out to us today. It is this knowledge that is providing detailed knowledge of the dramatic increase in air and sea temperature that characterises climate change as we know it.
In principle the process is quite simple. Digital images of the logs are taken and the data recorded in an international databank. This can then be manipulated to provide sophisticated re-creations of climate on single voyages, in distinct sea areas, or for the world itself. Necessarily there are some gaps in that data. In the age of sail, for example, the ships took predictable sailing routes, restricted by the direction of the prevailing wind and the known location of safe landfalls. The tracks of millions of voyages, therefore, run like deep scars across the oceans.
However, the tracks of explorers such as Cook, Vancouver and Flinders who pioneered western exploration of the Pacific, that of the Beagle, in which Darwin developed his theories of evolution, or that of Shackleton’s Endurance in its doomed voyage to the south pole, leave traces of delicate silky threads in the vastness of the unknown. These voyages, as voyages of science and exploration, all provide data of exceptional variety and quality, but the most basic data of the earliest log-books – those made before barometers or thermometers were invented – can still be used to illustrate historical climate over long periods or specific events such as the Great Storm of 1703, the fiercest hurricane ever to hit British shores in which four British warships foundered and an estimated 10,000 lives were lost.
From a global perspective there are also some gaps according to nationality. French, Spanish, Dutch, American, even Chilean naval logs all survive, but the majority of log books of the Japanese Navy which would have been invaluable for expanding our knowledge of climate change in the Pacific, were destroyed in the chaos at end of the Second World War. Similarly, the great Lisbon earthquake of 1750 destroyed records of the earliest Portuguese seafarers from the age of discovery. Nevertheless, it is the logs of ships that for centuries fought each other for control of the sea that are now being used to fight the war against climate change.
The digitisation of the logs has also created a stunning resource for historians to exploit. They also record punishment, death and disease, even daily accidents - it is surprising how many sailors dropped cannon balls on their feet. They record the details of battle, damage received, men killed and wounded. For vessels of exploration they even record initial contact with people whose first sight of western civilisation was an armed warship. The finest examples are illustrated by the officers, with sketches of landscapes that are now lost to history.
To see these is to look through the eyes of a sailor, to stand on the heaving decks of a warship and gaze on an unknown land a quarter of a century ago. For both historians and scientists the liberation of this resource is one of the most tantalising promises of the twenty-first century.
For more information, see the ACRE, CLIWOC and RECLAIM websites, all projects involved in the recreation of historic climate.
http://brohan.org/hadobs/acre/acre.html
http://www.ucm.es/info/cliwoc
http://icoads.noaa.gov/reclaim
Dr Sam Willis is an Honorary Fellow at the University of Exeter Centre for Maritime Historical Studies. He is the author of Fighting at Sea in the Eighteenth Century: The Art of Sailing Warfare, Fighting Ships 1750-1850 and Fighting Ships 1850-1950. He has worked as a maritime history consultant for Christie's and the BBC.