Growing Scientific Consensus

“Greenhouse gases are accumulating in Earth’s atmosphere as a result of human activities, causing surface air temperatures and subsurface ocean temperatures to rise.”
– Climate Chance Science, U.S. National Academy of Sciences, 2001

The earth is warming. Temperatures at the Earth’s surface increased by an estimated 0.6°C over the 20th century. The 1990's were the hottest decade of the entire century; perhaps even the millennium, and 1998, 2001, and 2002 were three of the hottest years ever recorded.

The growing scientific consensus is that this warming is largely the result of emissions of carbon dioxide and other greenhouse gases from human activities including industrial processes, fossil fuel combustion, and changes in land use, such as deforestation. Modeling of climate change scenarios by the IPCC in its report of Working Group 1 for the Fourth Assessment Report provided “best estimate” projections of future warming suggest a global increase 1.8°C to 4.0°C by 2100, with warming in some regions expected to be even higher. In addition to warming, increases in sea level and changes in precipitation, including more frequent floods and droughts, are possible if not likely. These changes, over time, are referred to broadly as "climate change".

Unaddressed, climate change will have significant impacts around the world. While some of the effects of climate change may be positive, such as longer growing seasons in the northern regions increasing the productivity of agriculture and forests, these positive impacts are unlikely to be sustained as the globe continues to warm. Furthermore, even while some nations as a whole may benefit, certain regions or sectors, such as the more southern areas may suffer. Similarly, many developing countries are even more vulnerable to the adverse impacts of climate change and less able to adapt. As nations continue to grow more interdependent, they may not be immune from impacts experienced elsewhere.

Even if we are able to reduce emissions of greenhouse gases, some further warming is unavoidable. We must plan and take action now to adapt to the changes we will face as our climate changes.

The above section is adapted from the Pew Center on Global Climate Change and the IPCC.