Lamont-Doherty Earth Laboratory of Columbia University just released a new set of Northern Hemisphere temperature data derived from tree rings that covers the last 1000 years. Tree rings are an important source of what is called “proxy” data, since scientists use information about how trees grow to determine the climate conditions which were affecting their growth, including temperature and precipitation. This serves as an independent data set to thermometer-based measurements of temperature, which have only been around for about 150 years and have some issues with siting.
The dataset shows both the fairly warm conditions about a thousand years ago, followed by generally declining temperatures until the mid 1800s, followed by rapidly warming conditions. Since these measurements were taken from trees that were located at high elevations in remote areas, they do not show any effects of urbanization or other land use changes.
You can read more at https://www.ldeo.columbia.edu/news-events/new-global-team-tracks-temperature-change-through-time?platform=hootsuite.
