The Arctic is already known as the region on the planet that is warming the fastest. But behind the familiar curves for average temperatures lies another and more disturbing story: Extreme weather events that can profoundly change ecosystems in just a few days. 

This is shown in a recently published a so called focus article by Professor Torben R. Christensen from Aarhus University in the journal Science Advances.

According to the article, research into climate and the environment in the Arctic has for decades been dominated by analyses of average temperatures, average precipitation, and slow trends such as “Arctic greening” and a gradual thawing of permafrost.

But new studies show that the Arctic is also entering a new era of bioclimatic extremes, where heat waves, droughts, rain on snow and sudden thaws in winter are occurring more frequently and over larger areas.

Analyses based on high-resolution weather data over seven decades indicate that almost a third of Arctic land areas today are exposed to types of extreme events that were largely absent in the mid-20th century, the article states.

When one event changes the ecosystem for years
What is special about extreme events is that they can push organisms and ecosystems beyond their limits of tolerance. 

According to the article, a single event of winter rain on snow can encase animals' food in ice and lead to widespread mortality in grazing animals such as musk oxen and reindeer. Similarly, the combination of heat waves and drought can trigger wilting damage to shrubs, drying out of soil and altered carbon exchange between soil, vegetation and the atmosphere.

These effects can occur in days or weeks, but affect populations and ecosystem functioning for years. This challenges both biodiversity, the food supply for local communities and our ability to predict future greenhouse gas emissions from the Arctic.

Affects the climate of the entire globe
According to the article, extreme weather in the Arctic is not just a local problem. Vegetation loss reduces CO₂ uptake, thawing permafrost can release large amounts of greenhouse gases, and changing snow conditions affect the Earth's reflection of sunlight. Thus, Arctic extreme weather events can act as reinforcing feedback on global warming. 

Decision-makers and management efforts should therefore, according to Professor Torben R. Christensen, incorporate scenarios with sudden and strong impacts – from infrastructure and preparedness to nature management and protection of vulnerable Arctic communities.

According to the article, in order to create these scenarios, two things are needed:
Firstly, more close and long-term monitoring in the Arctic, where weather stations, remote sensing and ecological measurements are linked, so that both climate extremes and the response of ecosystems can be monitored. 

Secondly, an adaptation of earth and climate system models so that they are not only calibrated to mean values, but can also handle frequency, intensity and compound extreme events.

The carbon balance must be seen in the entire landscape
The article particularly highlights the need to view the carbon cycle in the Arctic as a so-called overall Net Ecosystem Carbon Balance (NECB). The concept covers both the absorption and emission of CO₂ and other gases, and the carbon that is transported through the landscape by streams, snow and ice.

Today, these types of carbon sources are often measured separately – for example, atmosphere-ecosystem exchange in one place and dissolved organic carbon in streams in another. 

According to the article, it is necessary to compile them into a comprehensive landscape-level account to assess whether an area as a whole is a carbon source or whether it can capture carbon, and how vulnerable the area is to both gradual changes and sudden extremes.

Read the full article “Beyond averages: Why Arctic extremes matter” in Science Advances her.

For further information, please contact Aarhus University, Professor Torben R. Christensen, Department of Ecoscience at +45 93509049 or via email: torben.christensen@ecos.au.dk