Weather and climate

Overview

WEATHER can be defined as the prevailing state of the atmosphere at a given moment, characterised by weather elements such as air temperature, wind, air pressure, and precipitation.

Data on weather elements is collected from the monitoring network (in Estonian), which in Estonia consists of meteorological, hydrometric, marsh and coastal stations, precipitation measurement stations and actinometry stations. While the mentioned stations carry out measurements on the surface of the ground, the processes taking place in the air layer close to the ground are studied at the Tallinn-Harku aerological station with the help of radio sondes. Remote monitoring is carried out by weather radars in Harku and Sürgavere. Meteorological data from the monitoring network are available on the Environment Agency's open data webpage (in Estonian).

CLIMATE, in a broader sense, is the set of states of the global climate system, or earth system, over a longer period of time, whereby the climate system includes the atmosphere (air), the hydrosphere (water), the cryosphere (ice), the lithosphere (earth crust and land surface) and the biosphere (living organisms).

The United Nations (UN) Global Climate Observing System (GCOS) and the European Union's Copernicus Climate Change Service (C3S) focus their reviews on global climate indicators, which include air and ocean temperature, atmospheric composition, ocean acidity and water level, and indicators describing the cryosphere.

In a narrower sense, climate is a long-term regime of weather based on the geographical location of the observed area and is characterised by both typical weather and the frequency of extreme weather conditions. The climate of an area is determined by all the weather that occurs there during a longer period of time.

Longer-term periods of weather are therefore often described using averages of weather elements: daily average, monthly average and annual average. Deviations from the average (or anomalies) and the frequency of occurrence of extreme weather events provide information about the climate and its changes.

CLIMATE NORMALS Long-term averages of weather elements, or climate normals characterise the climate and its changes. According to the agreement between the World Meteorological Organization (WMO) member states, climate normals are calculated based on 30-year time series. This time period is long enough for extreme phenomena not to affect the average too much and small enough for changes to be recorded. These time series are called reference periods or normal periods. Although the WMO still recommends using the period 1961–1990 as a reference period for historical comparisons and describing climate change, climate normals should also be updated after every decade to reflect subsequent climate changes and their impact on our daily lives. In Estonia, new climate normals for the reference period 1991–2020 were introduced in 2021. You can read about the calculation of climate normals in the WMO 'Guide to Climatological Practices'.