Change scenarios for the Baltic Sea

This page presents a summary of the findings of the second assessment of climate change for the Baltic Sea Basin (BACC II) published in 2008. This second edition comes 7 years after the BACC I. It is a peer reviewed public access document covering recent, future and long term climate changes in the Baltic sea, its drivers and the their environmental and socio-economic impact. Some of the data below are extracted from a PowerPoint presentation conducted in October 2017 by Martin Stendel, on the behalf of the BACC II team.

Temperature anomaly in °C by year, source: BACC II, page 6, fig 1.1

Change in air temperature

Significant warming trend over past 30 years in all seasons and areas
More important in northern areas (>60°N, +0.08-015°C/10y) compared to southern areas ( +0.04-0.10°C/10y)
More important in wintern and spring (+0.10-0.15°C/10y) compared to summer and autumn (+0.04-0.10°C/10y)

Change in total precipitation between 1994–2008 and 1979–1993 by season based on SMHI data (Lehmann et al.2011). Adapted from BACC II, page 7, fig 1.2

Change in precipitations

No long-term trend was observed for precipitation
Some indication of an increased duration of precipitation periods
Possibly an increased risk of extreme precipitation events.

Storminess: number of lows with p_core< 980 hPa in Stockholm and Lund, source BACC II, page 7, fig 1.2

Change in wind and pressure

No significant change in wind speed
No long-term trend was observed for storminess

Ice breakup dates on river Daugava, in days relative to 1st January, source Kļaviņš et al. 2009, in Martin Stendel presentation.

Change in river and lake ice

Change in freeze-up and breakup dates
Decrease in duration of ice cover
Decrease ice thickness

Anomalies of the annual and decadal moving average of the modelled Baltic Sea spatial mean water temperature over the period 1500–2001. The dotted horizontal lines are the standard deviations of water temperature during the reference period 1900–1999 (Hansson and Omstedt 2008), in BACC II, page 134, fig 7.3

Change in sea surface temperature

Current sea warming lies within the range in past 500 years
The XXth century is the warmest, with the exception of the warm anomaly around the 1730s
Strong surface warming in Bothian Bay and Gulf of Finland since 1990
Detectable warming in deep water as well

The maximum extent of sea ice cover in the Baltic Sea, 1900–2012. The red line shows a long-term declining trend of *2 % per decade. Source BACC II, page 148, fig 8.3

Change in sea ice-extent in the Baltic sea

Increase in frequency of mild ice winters
Around 2% ice cover decrease per decade
Winter 2007-2008, with lowest ice cover ever recorded

Annual sea level means averaged for 14 Swedish sea level records corrected for land uplift and compared to the 1886 level. Black line: time-filtered version together with the filtered Stockholm sea level time series (red line) (Hammarklint 2009). Source BACC II, page 164, fig 9.5

Change in sea water levels, corrected for land uplift

The values below are corrected to eliminate the effect of the land uplift when estimating the sea water level.

Global rise of sea level estimated at 1.7 mm/year ± 0,5
Rise of sea level in the Baltic Sea estimated at 1.3 mm/yr – 1,8 mm/year

Time series of three quantiles (median, and the 1 and 99 % quantiles) of the distribution of de-seasonalised monthly sea level at several stations of the Baltic Sea in the period 1890–2010 (Barbosa 2008) in BACC II, page 166, fig 9.8

Overall change in sea water levels

The graphs on the left are showing to overall sea level for 12 locations in the baltic over the past 120 years. The straight bold line trend takes into account the land uplift as well as the rise in sea level.

The land uplift outmatches significantly the sea level rise in the Bothnian Bay (Ratan, Oulu) and to a lower degree in Stockholm, Landsort and Helsinki.
The sea water level rise is noticeable along the southern shore of the Baltic sea (Warnemünde, Wismar, Gedser), where the land uplift is minimal.

Anticipated changes for 2070-2099

Air temperature

Overall warming, 4-8°C in winter and 1.5-4°C in summer
Strongest change in the North of the Baltic Sea

Precipitations

Generally wetter
Possibly dryer in summer and in the south

Wind speed

No change

Runoff

Increase of 15 to 22% in runoff
Earlier peaks
Decreasing salinity?

Sea surface temperatures:

Projected increase of sea surface temperatures,
Up to 4°C in the summer in the north ,
Up to 2°C increase in deep water temperatures

Salinity

Changes uniform across seasons,
Small reduction in the northern and central parts,
Larger reduction in the Kattegat and Skagerrak

Sea ice extent

50 to 80% decrease of sea ice extent projected
Shortened ice season expected

Right panel shows the projected regional sea-level rise for 2090–2099 relative to the 1990–1999 baseline under the SRES A1B scenario, decomposed into local sea-level rise (upper left) and glacial isostatic adjustment (lower left; Hill et al.2010) in BACC II, page 260, fig 14.3

Scenario for sea level change 2090-2099

The graph on the left corresponds to the average scenario
The land uplift is still going to positively compensate for the sea level increase in Sweden above 60°N, but the sae level will increase up to half a meter in southern Sweden;
The up end scenario calls for a sea level increase all over the Battic sea, ranging from 10 cm in the north to one metre in the shouth.