1: WeatherWeather and climate are related but they differ in the time scales of changes and their predictability. Weather is the instantaneous state of the atmosphere around us. Temperature, precipitation, humidity, air pressure, cloudiness, radiation, wind, and visibility vary from day to day and over weeks and months. Weather predictability is limited to days. Climate is the statistics of weather over a longer period. It can be thought of as the average weather that varies slowly over periods of mont 2: ObservationsAlthough Earth’s climate is currently changing rapidly relative to past changes, in most regions where we live changes are slow enough that we do not notice them directly during our daily lives. In this chapter we will discuss some observations from the past 100 years and data from regions that are particularly sensitive to climate change, where the most dramatic effects have occurred. 3: PaleoclimateMeasurements with modern instruments (the instrumental record) are available only for roughly the past century. This is insufficient to describe the full natural variability of the climate system, which makes attribution of observed changes difficult. We want to know if the changes observed in the recent past are unusual compared to pre-industrial climate variability. If they are it is more likely that they are anthropogenic, if not they could well be natural. 4: TheoryWe have seen how global climate has changed and we’ve learned that some of these changes have been related to forcings and feedbacks such as atmospheric CO2 concentrations and the seasonal distribution of solar irradiance. Now we want to proceed to understand quantitatively why climate is changing. 5: CarbonDue to the importance of CO2 as a greenhouse gas the carbon cycle is a crucial part of the climate system. Since carbon exchanges with the biosphere, biological processes need to be considered in climate science. The carbon cycle is part of the broader biogeochemical cycles, which include other biologically important chemical elements such as nitrogen and oxygen. 6: ProcessesMany different processes play important roles in the climate system. In chapter 4 we have already learned about radiation and the global energy budget. Here we want to discuss atmospheric and oceanic circulations, how they transport heat and water, and we’ll explore a little more in depth Earth’s water cycle and how it penetrates all climate system components and is linked to the energy cycle. 7: ModelsClimate models are tools used in climate research. They are attempts to synthesize our theoretical and empirical knowledge of the climate system in a computer code. This chapter describes how climate models are constructed, and how they are evaluated, and it discusses some applications. 8: ImpactsClimate change impacts not only physical but also biological and human systems. Possible impacts of future climate change are important considerations for current decision making, but they are associated with uncertainties. In this chapter we will discuss future projections with climate models, the main sources of uncertainty for those projections, and some global scale impacts. 9: EconomicsUnderstanding the impacts of climate change requires a combined understanding of how ecosystems respond to the buildup of greenhouse gases and how humans are impacted and thus respond to the changes in these ecosystems. This chapter provides an economic perspective on the climate change challenge and an introduction to the role that market-based incentives and policy can play in helping us mitigate and adapt to the impacts of climate change. 10: EthicsTo the surprise and frustration of the scientists, all nations are not taking immediate action to slow climate change, and people are largely silent, even acquiescent, in the face of real threats to their futures and the futures of all beings that evolved under this – not another, hotter, more volatile and violent – climate. 11: SolutionsClimate change is a difficult problem to solve because our modern society was build with fossil fuel burning as an energy source. We still depend strongly on fossil fuel energy for everything from driving our cars and washing our laundry to charging our cell phones and heating our homes. In order to stabilize climate, however, we’ll need to move to near-zero carbon emissions in the long run. Thus, the challenge is to decarbonize our economy.