Climate Change is Real

Carbon Dioxide Concentrations Chart. Credit: U.S. Global Change Research Program

Worldwide scientific consensus tells us that human activities have led to large increases in the concentrations of carbon dioxide, methane, nitrous oxide and other heat-trapping gases, also known as greenhouse gases, in the Earth’s atmosphere during the past century. Global temperatures are projected to continue to rise over this century; by how much and for how long depends on a number of factors, including the amount of heat-trapping gas emissions and how sensitive the climate is to those emissions.

Climate change is not a distant threat; it is occurring here and now. As a result of the growing abundance of these greenhouse gases, the global average air temperature has risen steadily over several decades, particularly since the 1950s. The first decade of the 21st century has proven to be the hottest decade since scientists began recording global temperatures in the 1880s, with the 1990s following close on its heels as the second hottest. The unmistakable signs of a rapidly changing climate are everywhere – melting glaciers, heat waves, rising seas, flowers blooming earlier, lakes freezing later, migratory birds delaying their flights south. No geographic region is immune.

According to the findings of the Intergovernmental Panel on Climate Change (IPCC), sea levels have been rising at an average rate of 1.7mm per year for much of the 20th century. However, in the last two decades, that rate has nearly doubled, reaching an average of 3mm per year. Many coastal regions, including a number of wildlife refuges and cities will be threatened as shorelines recede. The 2007 IPCC report predicts that sea levels will rise 0.18 to 0.59 meters in the coming century, however, more recent studies taking into account observed changes in the melting of the ice sheets in Greenland and Antarctica have suggested that this figure is too conservative, instead projecting a rise of up to 2 meters by 2100.

Rising temperatures and particularly rising ocean temperatures also have significant implications for the world’s rainfall patterns. The heat causes water to evaporate faster, resulting in more water in the atmosphere. Scientists predict that the global average annual precipitation will increase as a result. However, this precipitation will not be distributed evenly across the globe. While the effects are predicted to vary from region to region, it will generally hold that already wet areas will get wetter while dry areas will get dryer. Many regions will also find rainfall patterns tending more towards the extreme, torrential downpours interspersed with prolonged dry spells, in other words rain storms will become more intense but less frequent. Also, in some areas precipitation that used to be in the form of snow will shift to rain, with major implications for streamflows and availability of water for wildlife, fish – and people.

For more information, visit the U.S. Global Change Research Program web site.

Last updated: April 16, 2014

Contact Us