Projections and uncertainty in the US climate change impacts report

The first two Key Findings from the recent USGRP report “Global Climate Change Impacts in the United States” are:

1. Global warming is unequivocal and primarily human-induced.

Global temperature has increased over the past 50 years. This observed increase is due primarily to human-induced emissions of heat-trapping gases.

2. Climate changes are underway in the United States and are projected to grow.

Climate-related changes are already observed in the United States and its coastal waters. These include increases in heavy downpours, rising temperature and sea level, rapidly retreating glaciers, thawing permafrost, lengthening growing seasons, lengthening ice-free seasons in the ocean and on lakes and rivers, earlier snowmelt, and alterations in river flows. These changes are projected to grow.

Both of these Key Findings are based on a combination of observational, theoretical and model based analyses and are a consensus opinion of the report's Lead Author team. After a brief discussion of these statements, the model based projections of future climate used in the report will be detailed. A discussion of the source and magnitudes of uncertainties in these projections will also be presented.