Reconstructing our Climate’s History: Old Logs and Written Records

Read...

Old Logs and Written Records

I want to touch on one more source of climate data, albeit one that isn't technically a proxy. Before the advent of modern meteorological instruments, early observers meticulously recorded weather conditions in logs, diaries, and other written records. Ship captains, for instance, often noted wind patterns, sea ice, and weather events during their voyages across the world’s oceans. Handwritten records from explorers, farmers, and even monks often contain detailed accounts of temperature, rainfall, and unusual events such as droughts, floods, or frosts. For instance, ship logs from the 18th and 19th centuries have been used to reconstruct historical sea ice extent in the Arctic and Antarctic. Likewise, personal diaries from farmers have revealed details about crop failures and harsh winters, which can indicate broader climate conditions.

While these observations are certainly not as precise as modern measurements many times they are qualitative, talking about "a great heat wave" instead of providing a numeric temperature they can help us piece together patterns of past climate and weather events, especially when combined with other sources of data, such as the ones above. They can also give us a picture albeit a fuzzy one of trends in extreme weather, like what hurricane landfalls may have looked like around the founding of the United States.

Stitching all of these together, we can get a more complete view of how the temperature of the planet has changed over geological time. The figure below shows estimates of the Earth's temperature from 500 million years ago (on the far left) to the present day (on the far right). We have a more detailed understanding of the temperature the closer we get to the present day, so the tick marks for time are change at each vertical break in the figure, starting with every 100 million years (100,000,000 years) in the first section and ending with every thousand years (1,000 years) on the right.

From this figure, we can see that the Earth’s temperature has changed drastically over the course of geological time. Within this period, many changes occurred: the continents changed positions, volcanic activity ramped up and ramped down, and the atmosphere had different amounts of carbon dioxide. In general, periods that are very warm over the Earth’s history are ones where the carbon dioxide is higher.  Over the past 11 thousand years the Earth’s temperature has been relatively constant, allowing humans to thrive. This is the case until very recently, when an increase in carbon dioxide created by people has led to a quick increase in temperature that is projected to continue, as depicted by the red dots representing projected temperatures for 2050 and 2100. Remember, the scale on the bottom is changing with each break. Although the Earth has been as warm as we are projecting it to become, it has never happened this quickly or when humans have been able to thrive.