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Scientific records show that the surface temperature of the Earth has risen by about 0.6°C in the last 100 years. The ten warmest years of the 20th century all occurred in the last 15 years of the century, with 1998 the warmest ever; 2001 was the second warmest year ever.
The great majority of the world's professional climate scientists now agree that most of the observed climate warming over the last 50 years is due to rising levels of greenhouse gases, caused by human activities. The two most important activities threatening climate are the burning of fossil fuels and the destruction of forests and vegetation both of which lead to an increase in the concentration of greenhouse gases in the Earth's atmosphere. 1 The impacts of these increases are expected to continue through this century. They include a changing climate, rises in sea level, and a host of effects on our social and economic systems.
How have climate scientists come to these conclusions? Exactly how do certain types of air pollution turn up the heat? Explore this section to learn more about how our climate system works, how we measure and predict changes in the climate from human activities, and what the impacts of climate change are likely to be. The body of scientific knowledge in this field is growing rapidly. You'll also find links to a number of the best scientific sources because thousands of climate and ecosystem scientists are working around the world to improve our understanding of climate change and its probable impacts on the environment, our economy, and our quality of life.
1. A very small minority of professional climate scientists do not agree with this conclusion, however. There is a range of perspectives and different approaches for taking them into account.