Extreme climates over a hundred thousand years

Brand new analyses show Swedish climate change over a very long period. Over a hundred thousand years, the mean annual temperature can vary by more than 30°C.

Erik Kjellström och Gustav Strandberg
"In the new research study we describe the limits within which the climate can be expected to vary by presenting three periods with extreme conditions," say climate researchers Erik Kjellström and Gustav Strandberg

A recently completed research project into the Swedish climate over a period of a hundred thousand years is filling in knowledge gaps about historical development, while also offering guidance on the future climate.

"Much of today´s climate research focuses on scenarios a hundred years into the future. However, we´re unable to specifically say if and exactly when anything will happen regarding more long-term development. In the new research study we describe the limits within which the climate can be expected to vary by presenting three scenarios of extreme conditions," says climate researcher Erik Kjellström, SMHI.

Permafrost, ice age, warmer climate

The three examples projected using climate models are a cold climate with limited ice cover, an ice age climate, and a future warm climate. The conditions used as a basis for the projections correspond to a period of permafrost 44,000 years ago and the most recent ice age 20,000 years ago. The warm example is intended to reflect the climate in 6,000 years.

"We know that carbon dioxide released into the atmosphere remains there for a very long time. The warm future period therefore shows very similar patterns to the scenarios for a hundred years time. The results also indicate that if Greenland´s ice melts, it will not reform."

The temperature differences between the warm and cold periods in the study are extremely great. The variation during the winter is particularly pronounced, where the mean temperature is more than 40°C higher in the warm period than during the ice age. The major differences in temperature climate are due not only to far a colder climate in general during the ice age, but also to the effect of the high inland ice on air temperature. Precipitation also varies between the periods, with more rain the warmer the climate.

Factors that affect the climate

One important aspect of the research project has been to map different factors that affect the climate, such as ice cover, land elevation and changes in vegetation. Warmer climates generally produce more vegetation, which in turn can cause further warming. Dust and particles also have a major impact on climate: during cold periods with lower sea levels, more dust blows up and has a cooling effect on the climate.

The climate projections have been analysed alongside climate information that can be gleaned from prehistoric pollen and algae. There is quite good access to this data in the Mediterranean area which provides an estimation of climate during different periods. There is, however, no such climate guidance for the ice age in Sweden, which is why the research is producing brand new material.

"The analysis is increasing knowledge of the climate during three extreme periods, and is also providing more insight into various links and repercussions, which we can utilise in our climate models. For the first time we have carried out climate projections for a very long time perspective, both on a global level and in more detail at a regional level," says Erik Kjellström.

The research has been conducted over a two-year period on behalf of SKB (the Swedish Nuclear Fuel and Waste Management Company) in collaboration with the Royal Institute of Technology, Lund University and Stockholm University.

Rapporten Climate conditions in Sweden in a 100.000‑year time perspective (pdf)