Length of the growing season in the Netherlands, 1900-2002

In the last fifteen years, the average growing season was more than three weeks longer than in 1961-1990.

Growing season more than three weeks longer

On average, during the last fifteen years, the growing season has been more than three weeks longer than in 1961-1990. In the period 1961-1990, the growing season lasted an average of 269 days. In the last fifteen years, the growing season has averaged 293 days, 24 days more than previously (KNMI, 2003).
The length of the growing season is determined as the number of days a year with an average temperature in De Bilt of more than 5°C. So there has been a considerable increase since the mid-eighties.

Increase in length of growing season follows the average temperature

The change in the length of the growing season matches the change in the average temperature in the Netherlands. In the last twenty years, this was approximately 1 ^oC higher than at the start of the 20^th century.
The enhanced greenhouse effect is probably the main cause. This in turn is the result of the increased emissions of greenhouse gases by human activity. The UN Climate Treaty (UNFCCC, 1992; Rio de Janeiro) and the Kyoto Protocol (UNFCC, 1997) include agreements about stabilising concentrations of greenhouse gases. The idea is that this will reduce the human impact on the climate.

Impact on nature

An early start to the growing season means that plants start growing earlier and grow faster. Faster plant growth also means an earlier start to the hay fever season. Heat-loving plant species have shifted northwards.
The higher temperatures and their effects on plant growth also affect animals. Many small varieties of butterfly now appear earlier than previously. In recent years, species of butterfly that normally live more to the south are also being observed more and more. Birds are also brooding earlier.

Climate change and the wasp spider, 1990-2002 (page is not available yet)

Temperatures are increasing so fast that not all plants and animals are expected to be able to adapt.

References

KNMI (2003). The Royal Netherlands Meteorological Institute is responsible for measuring temperatures in the Netherlands.

UNFCCC (1992). United Nations Framework Convention on Climate Change Rio de Janeiro, 1992.

UNFCCC (1997). Kyoto Protocol to the United Nations Framework Convention on Climate Change. Kyoto, 11 December 1997. Link to PDF file. Link to HTML version.

Relevant information outside of the Environmental Data Compendium

Information about the Climate Treaty and the Kyoto Protocol can be found on the website of the United Nations Framework Convention on Climate Change (UNFCCC).

Information about Dutch climate policy can be found on the website of the Ministry of Housing, Spatial Planning and the Environment.

More information about the effects of climate change on the weather can be found on the website of the Royal Netherlands Meteorological Institute.

More information about climate change and concentrations of greenhouse gases can be found on the websites of the IPCC (Intergovernmental Panel on Climate Change) and ETC/ACC (European Topic Center on Air and Climate Change).

Information about current and future developments for the Kyoto Protocol can be found in Environmental Balance 2003 and Milieuverkenning 2000-2030, both RIVM publications.