Climate change

Climate change is one of the greatest environmental problems facing mankind, and one for which mankind is largely to blame. The continuous emission of greenhouse gases, such as carbon dioxide, since the Industrial Revolution, has led to continuous global warming. Other factors, such as the changing use of land, increased solar activity, and changes in particulate matter and soot particles have also contributed to climate change.  

Over longer time scales, other processes can also play a role in climate change (e.g. of a geological or astronomical nature). Over short time scales (a number of years), natural variations in weather and in the El Niño/La Niña cycle are especially important, as well as the effects of major volcanic eruptions.  

Our research focuses on existing climate change, and specifically on the role that greenhouse gases and particulate matter play in this. Due to the global nature of climate change, research is carried out in national cooperation, both nationally and internationally, with numerous partners such as VU-A, WUR, KNMI, INRA, MPI-BGC, LSCE, etc.  

Aerosol and climate

Of the factors that contribute to climate change, the influence of particulate matter, so-called aerosols, is subject to the greatest uncertainty. Aerosols can reflect light, causing less sunlight to reach the earth’s surface. This has a cooling effect on the climate (the “direct effect”). Aerosols also contribute to cloud formation. They act as the nuclei on which water vapour can condense and in turn form cloud drops. Clouds have a cooling effect (on average) and aerosols therefore also have an indirect effect on the climate via their influence on cloud formation. There is also a set of particulates (primarily soot) that actually have a warming effect because they absorb solar radiation.  

Compared to greenhouse gases, aerosols only have a short life span in the atmosphere. After no more than a few weeks, they are absorbed into the earth’s surface again. They therefore only have a localised and limited effect on the climate, unlike greenhouse gases that have a longer life span.  

Aerosols have probably contributed greatly to climate change during the past 100 years. Aerosol concentration increased significantly in the mid 20th century, thereby halting warming caused by greenhouse gases. Over the past decades, the global concentration has remained relatively constant, allowing global warming to continue as a result. The greater concentration of particulate matter in relation to before the Industrial Revolution has masked global warming by greenhouse gases to a degree. Future reductions in particulate matter emissions, such as in the context of improving air quality, could therefore cause additional global warming.  

In addition to the climatic effects of particulate matter, negative health effects are also important for any policy measures. How the effect of a package of emission measures on the climate will differ locally, and how all of this works out in the end is shrouded in uncertainty. It is therefore highly desirable to have a greater knowledge of the origin, physical manifestations, conversions in the atmosphere, the manners in which particles disappear again and how they influence the radiation balance of the earth in the meantime, directly or via cloud formation.  

ECN is participating in the following projects, among others, to this end:

• BSIK CS4

Greenhouse gases

Greenhouse gases absorb infrared radiation emitted by the earth and then re-emit it in all directions. This characteristic of some substances was already observed in the laboratory more than 150 years ago. The presence of greenhouse gases in the atmosphere increases the temperature because less radiation vanishes into space. The natural greenhouse effect is caused primarily by water vapour and carbon dioxide. Without this natural greenhouse effect, the temperature on earth would be roughly 30 degrees colder and therefore not suitable for existing life.  

Since the Industrial Revolution, mankind has increased the concentration of greenhouse gases in the atmosphere considerably. The most important greenhouse gases, which are emitted through the fault of mankind, are carbon dioxide, methane, nitrous oxide, CFCs and ozone. These emissions are largely due to the combustion of fossil fuels. Intensive farming, deforestation, dewatering and industrial processes are also important sources. Most greenhouse gases (except ozone and water vapour) have a long life span in the atmosphere (between 10 and 1000 years). The warming effects are therefore global and long term (unlike those of aerosols).  

The precise emissions of the most important greenhouse gases are still uncertain. We think that overall global carbon dioxide emissions due to fossil fuel combustion are a few percentage points. Our knowledge of emissions from wood-fired ovens is less precise, and emissions from forest fires and the deforestation of tropical rainforests are very uncertain.  

The knowledge of emissions is less precise than global averages across relatively small surfaces and short time periods. Annual, national emissions from agriculture, for example, peat oxidation after dewatering, methane from cows and ditches, and nitrous oxide from fertilised pastures are uncertain up until a factor of two. This is despite the fact that there are actually binding agreements in the Kyoto Treaty and other future climate treaties relating to these national emission figures.  

Due to these treaties, the policy has an effect on these specific sources and their emissions. In order to evaluate that policy, an independent emissions check is required. To that end, observations, direct flux measurements of various sources and integrated measurements over time concerning the effect of emissions across large areas are needed. Atmospheric transport models are used to translate concentration measurements into emissions per area. ECN also participates in the following projects for that purpose:

• BSIK ME-1 and ME-2
• Carbo-Europe IP, GEOMON and IMECC
• ICOS and ICOS-NL
• TTorch (coordinator)

Measuring equipment

• Licor
• QCL
• GC
• SMPS
• CCN counter  

Measurement strategy

Cabauw

The 200-metre-high measurement tower in Cabauw (in the Dutch province of Noord-Brabant) is used for numerous measurements. ECN measures various greenhouse gases here (carbon dioxide, methane, nitrous oxide, sulphur hexafluoride) and other air pollutants (nitrogen oxides, carbon oxide, hydrogen, radon, etc.). We also measure the chemical composition of aerosols using instruments that have often been developed by ECN. Other institutes measure meteorological variables (KNMI – Royal Netherlands Meteorological Institute) and the physical properties of aerosols (TNO).  

The Cabauw tower is part of a growing network of tall measuring towers in Europe. Due to the height at which measurements are carried out on these towers, they are representative for a relatively large surface area as they are influenced less by local emissions compared to measurements carried out on the surface of the earth. This makes them ideal for estimating emissions of greenhouse gases, for example. Some modelling work is required, however, which also introduces uncertainty in turn. By averaging across large surface areas and long time periods, an attempt is made to keep this degree uncertainty within limits.  

Cloud chamber

The ECN cloud chamber is unique and already has a long history. It is actually a metal vat (7 m3) through which outside air can be blown. This air can be filtered first if desired (removal of particulate matter) and brought to a specific humidity. A relatively small supersaturation, which also occurs in natural stratus clouds, can be kept in a stable state for hours on end. This makes the chamber highly suitable for calibrating measuring instruments, but also for studying processes that occur in clouds.  

Measuring vehicle

• CESAR

Computer models

• COMET
• FLEXPART
• WRF