The Earth climate system contains a vast range of processes and feedbacks, so it is natural to focus first on the dominant ones, for example, those dominating planetary heat and carbon budgets. However, these basic processes have been modeled with increasing accuracy since the days of Arrhenius (1896a,b). Nowadays, we seek to improve representation and quantify the uncertainty of many more processes. Quite often dominant processes modulate the subdominant, and vice versa, with a whole cascade of reciprocal actions and feedbacks. This last point, feedback, is where difficulties arise, particularly if it occurs within interactions spanning multiple scales. Then practical difficulties of measuring the relevant interactions or the excessive computer power required for simulation limit our development of theoretical and quantitative assessment of how important these feedbacks may be. In this situation, we take a shortcut and use a parameterization that summarizes one, or several, processes into a simplified algorithm. Progress, bias analysis, and experience tell us how much further we need to go to have more accurate and reliable results. Today it is obvious that the atmosphere and ocean are heavily interacting-enormous quantities of heat, energy, water vapor, and carbon dioxide are exchanged each instant through their boundary layers. After the overall radiation balance, these exchange processes are the next priority in providing predictions of the climate system from seasons to centuries. The role of these exchanges is clear, in that the heat capacity of only a few meters of the ocean equals that of the whole atmosphere, and the carbon reservoir of the ocean dwarfs all but the lithosphere. However, having in mind the scale of the planet, it is natural to look at the problem on a large scale. Waves are small in comparison, a tiny distributed detail. However, it is a beautiful example of the little process modulating the overall large-scale behavior. Granted that some of the small-scale processes do affect the large-scale ones, the question is how much they affect the climate. One point of view is that the climate is established by the overall budget of incoming and outgoing radiation. Even if this is the case, two aspects need to be pointed out. First, the distribution of temperature and other parameters will vary based on small-scale processes rather than overall balances, and such distributions and their variations are relevant to humans even if they only slightly affect the global energy balance. Second, as climate is progressively changing through natural and anthropogenic changes, we live in a permanent transient situation. Only application of our best physical principles, rather than empirical parameterizations, can be robust in the face of a changing climate. Science has been slow to appreciate the extent of the interaction between ocean and the atmosphere. It took even longer to understand how these exchanges are modulated by the characteristics of the surface that separates the two phases. Here, we have tried to emphasize how sea state, particularly during wave-breaking conditions and when waves are not equilibrated with the wind, strongly modulates many of the processes that have a direct influence on climate. We still do not grasp the whole physics nor an accurate measure of the degree to which the mean state and climate feedbacks are affected by these modulations, but having an idea of where we want to go is certainly a good start. Many groups worldwide are attempting to quantify these effects of waves on climate in observations, models, and theory, and we celebrate their accomplishments and look forward to their discoveries. We need to carry on, understanding more and more the physics of the thin layer of fluid that, in the immensity of space, surrounds the planet that is our home. © 2012 American Meteorological Society.
