Current Climate

Trends and Significant Change against Natural Variability

Trends in climate — past, present and future — always need to be understood in the context of the naturally occurring variability. Climate variability here, refers to the ways how climate conditions (e.g., temperature and precipitation) “flicker” from year to year within their respective typical “range of variability”. The cause for this natural variability can be due to quasi random internal variability of the coupled atmosphere-ocean-land-ice system (as weather variability is drawn out over many years). A prime example for a cause of that category is the variability induced by El Niño – Southern Oscillation. Other causes can be the influence from periodic “forcing” events of non-human nature, such as explosive volcanic eruptions. These natural factors (internal as well as natural forcing) are summarized under “internal climate variability”. This internal climate variability is always present, sometimes a bit more exaggerated, sometimes a bit less. A climatology, therefore, has to be understood as a mean with variability around it. Variability can be very large from year to year (i.e., the high latitudes), and in a few locations, and for specific variables, it can be small (i.e., temperatures in the tropics).

In contrast to natural variability, anthropogenic emissions of greenhouse gases and resulting changes in atmospheric concentrations (i.e., CO2, methane) together land surface changes and aerosol impose a different forcing on the climate system. The search for climate change signals tries to separate their effects from the natural background variability. That signal can show as changes in the magnitude of the variability as well as through a systematic trend overtime.

This page offers three themes in which to explore and understand differences in variability, trends, and significance of change across the last 70-, 50- and 30-year periods. It is meant as an informational tool to augment the views from the climatology pages (Current Climatology- Climatology tab). The three sections present different aspects of how variability might need to be taken into account. For simplicity of navigation, the variables presented are only a subset of the full indicator catalog.  Data used on this page is derived from the ERA5 reanalysis (here used at 0.5º x 0.5º resolution) in order to extract also the daily variability. See  in each visual for discussion on how to interpret data presentations. 

I – Trends within Variability

Climatological averages and trends need to be seen relative to the inter-annual variability

(95th Percentile Not Met) :

II – Variability and Change in Variability

Trends don’t necessarily imply a simple shift in climate and its variability envelope. Changes in variability can be very important for both climatic means as well as at the weather scale (extremes).

III – Change and Significance

Trends determined on different length of timeseries can be a good indicator of change. A period dominated by natural variability (low trend) can be seen in contrast to the emergence of an (anthropogenically) forced trend.