Emissions from fossil fuel combustion alter the composition of the atmosphere and have been touted as a major cause of climate change. The amount of carbon dioxide in the atmosphere, for example, has increased by more than 30% since pre-industrial times. Average global surface temperature has increased by approximately 0.6 ± 0.2°C since the late 19th Century, and surface temperature records indicate that the 1990s are likely to have been the warmest decade of the last millennium. The anthropogenically-induced warming is superimposed on natural climatic variability. Proxy records show a regular oscillation, on a roughly 100,000-year cycle, between glacials and interglacials. Superimposed on these long-term oscillations are shorter scale variations. It is thought that changes in the seasonality and location of radiation from the Sun trigger the onset or end of glaciation, and the change is then amplified by feedbacks in the earth-atmosphere system. A firm link between atmospheric composition and temperature has been established from ice core records spanning the last 420,000 years, which show that changes in time of global temperature and atmospheric concentrations of carbon dioxide and methane are tightly coupled. Global average surface temperature is projected to increase by between 1.4 and 5.8°C by 2100, with the warming being greatest over land and polar regions. Precipitation is predicted to increase in the tropical, mid- and high-latitude regions, but to decrease in the subtropical regions. Alternative energy technologies such as hydrogen fuel cell vehicles will lower greenhouse gas emissions and reduce climate problems and costs.