White Christmas, open air events without rain or in agriculture – the weather is important in many aspects of our daily life. From time to time, we would like to change it. But can we specifically influence it?
If we aim to control weather, we first have to understand the correlation between different weather phenomena. But, actually, weather forecasts only indicate a probability about how the weather will most likely be on the next day. These forecasts are based upon numerical simulations, because weather phenomena are the result of nonlinear dynamics. They cannot be described by analytic solutions, but rather have to be described by means of chaos theory. The most prominent example is the so called “butterfly effect”: A small change in the initial conditions (e.g. the flapping of a butterfly’s wings) leads to a big difference in the outcome. In this case, the result is not a compulsory consequence – not to be mixed up with the snowball effect! But if forecasts are already difficult, can we succeed in controlling the weather?
For example, lightning rods are a tool to influence the weather. It also seems possible that silver iodide can be used for cloud seeding and, therefore, to induce rain or suppress hail. But scientific evidence is still missing.[2, 3] Several ideas to prevent hurricanes have been gathered in a documentary in 2007. They include the removal of electrical charge by means of lasers or the cooling of the surface of the ocean with liquid nitrogen to deprive the heat energy of an oncoming hurricane.
In spite of several interesting applications, we are far away from controlling the weather. Mostly, we neither understand the complete outcome of such interventions, nor can we calculate them quantitatively. The future will show whether we can specifically influence the weather some day with all its chaotic effects.
 J. Slingo, T. Palmer, Uncertainty in weather and climate prediction, Philosophical transactions Series A, Mathematical, physical, and engineering sciences, 369, 2011.
 B. A. Silverman, A Critical Assessment of Hygroscopic Seeding of Convective Clouds for Rainfall Enhancement, Bull. Amer. Meteor. Soc., 84, 2003.
 Z. Levin, N. Halfon, P. Alpert, Reassessment of rain enhancement experiments and operations in Israel including synoptic considerations, Atmospheric Research, 97, 2010.