Data Sources

Question 1

What is the difference between direct and indirect data sources?

Answer 1

Direct records: historical observations of weather, sea ice etc., which have been stored in an archive
Indirect records
frosts)
- Records of weather-dependent natural phenomena (e.g. droughts, floods, lake/sea ice freeze and break up timing)
- Phenological proxies (dates of flower of buds and trees, harvests)
- Picture records

Question 2

Indirect example

Answer 2

Date of grape harvest in France. Taken from tax records.

Warmer years tend to have a later harvest, as they can get a better yield. Higher tax returns.

Calibrated to Paris temperatures where overlap for late 1700s and 1800s. . The mean for April to September has a correlation of over 0.8 which is good.

But temperature is not the only factor that affects, demand for goods, droughts etc will all affect.

Question 3

Example of indirect (ships)

Answer 3

Ship records in Stockholm.

Ship records– when was last boat of autumn, when was
first in spring… 1700s and 1800s.
ii) Tolag (duty on goods transported by sea)
iii) Sea passports (issued to insure against Mediterranean piracy)
Personal diaries of when ice broke up

Calibrated against temperatures (started recording in 1750s).
Good measure for winter temperature and things like tree rings are mostly summer temperatures.

Good for mean temperatures, bad for extremes.

(difficult if a mild winter when ships could sail all season)

Question 4

Pros and cons of ships logbook data

Answer 4

The observations are fixed in space (lat/long) and time (dated)
The observations are homogenous in respect of time of observation (noon) and of recording (standard, pre-Beaufort vocabulary)
Observations are made AT SEA thereby filling a spatial gap Data are not proxy, and record conditions at the time
The source is one of great abundance

But the term gale was used for wind, so have to adjust meaning.
And be careful of anecdotes.