What causes global warming
what causes global warming? is the biggest factor in determining future global warming is projecting future emissions of CO2 and other greenhouse gases—which in turn depend on how people will produce and use energy, what national and international policies might be implemented to control emissions, and what new technologies might become available. Scientists try to account for these uncertainties by developing different scenarios of how future emissions—and hence climate forcing—will evolve. Each of these scenarios is based on estimates of how different socioeconomic, technological, and policy factors will change over time, including population growth, economic activity, energy-conservation practices, energy technologies, and land use. Scientists use climate models to project how the climate system will respond to different scenarios of future greenhouse gas concentrations. Typically, many different models are used, each developed by a different modeling team.
Each model uses a slightly different set of mathematical equations to represent how the atmosphere, oceans, and other parts of the climate system interact with each other and evolve over time. Models are routinely compared with one another and tested against observations to evaluate the accuracy and robustness of model predictions. The most comprehensive suite of modeling experiments to project global climate changes was completed in 2005.1 It included 23 different models from groups around the world, each of which used the same set of greenhouse gas emissions scenarios. Shows projected global temperature changes associated with high, medium-high, and low future emissions (and also the “committed” warming—warming that will occur as a result of greenhouse gases that have already been emitted). Continued warming is projected for all three future emission scenarios, but sharp differences in global average temperature are clearly evident by the end of the century, with a total temperature increase in 2100, relative to the late 20th century, ranging from less than 2°F (1.1°C) for the low emissions scenario to more than 11°F (6.1°C) for the high emissions scenario. These results show that human decisions can have a very large influence on the magnitude of future climate change.