Abstract

A strong consensus among climate scientists has emerged on key aspects of global climate change: humans have unquestionably altered the composition of the atmosphere in significant ways, there has been an increase in global average temperature of 0.4 – 0.8°C (0.7 – 1.5°F) in the past 100 years, and this increase in temperature is probably caused in part by the atmospheric changes wrought by humans. In the future, the accumulation of greenhouse gases is expected to lead to further warming of 1.4 – 5.8°C (2.5 – 10.4°F) by 2100, with moderate (at the low end) to dramatic (at the high end) consequences for humans and global ecosystems. The uncertainty in this wide range of estimates stems about equally from uncertainty about natural feedbacks in the climate system and from estimates of future socioeconomic change.< br/>
Climate models are the best tool available for understanding future climate change. CIG has extracted output for the PNW region from eight global climate model simulations, which taken together project a regional warming of 1.7 – 3.5°C (3.1 – 6.3°F) by the 2040s, with modest increases in winter precipitation. Even with wetter winters, however, the region will likely face reduced summer flows as rising temperatures reduce winter snowpack depth and distribution. Climate models simulate large-scale temperature much better than other quantities like precipitation; consequently, confidence in the projections of future temperature is higher than for other climate variables. Climate change is expected to continue beyond the 2040s and probably even beyond 2100.