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comparable to those of the eastern plains, while average winter temperatures are somewhat lower <br /> than at similar elevations in the plains. <br /> Precipitation west of the Continental Divide is more evenly distributed throughout the year than <br /> on the eastern plains. For most of western Colorado,the greatest monthly precipitation occurs in <br /> the winter months, while June is the driest month. In contrast, June is one of the wetter months in <br /> most of the eastern portions of the State. <br /> Greenhouse Gases and Climate Change <br /> There is broad scientific consensus that human actions are changing the chemical composition of <br /> Earth's atmosphere. Activities such as fossil fuel combustion, industrialization, deforestation, <br /> and other changes in land use are resulting in the accumulation of trace greenhouse gases <br /> (GHGs) such as carbon dioxide (CO2), methane (CH4), nitrous oxide (N20), and several <br /> industrial gases in the Earth's atmosphere. <br /> Between 1750 and 2011, cumulative anthropogenic CO2 emissions emitted to the atmosphere <br /> were approximately 2040 ± 310 GtCO2. About 43% of these emissions have remained in the <br /> atmosphere (880± 35 GtCO2); the rest was removed from the atmosphere and stored in natural <br /> terrestrial ecosystems (plants and soils—29%) and in the oceans (28%). Although CO2 levels in <br /> the atmosphere have varied perpetually throughout Earth's history (along with corresponding <br /> variations in climatic conditions), industrialization and the burning of carbon based fossil fuel <br /> sources has caused CO2 concentrations to increase measurably, from approximately 280 ppm in <br /> 1750 to 400 ppm in 2015. The rate of change has also been increasing. This fact is demonstrated <br /> by data from the Mauna Loa CO2 monitor in Hawaii that documents atmospheric concentrations <br /> Of CO2 going back to 1960, at which point the average annual concentration was recorded at <br /> approximately 317 ppm. The record shows that approximately 70% of the increases in <br /> atmospheric CO2 concentration since pre-industrial times (1750) occurred within the last 55 <br /> years. The trend corresponds to an increasing population and rising standards of living and <br /> modernization around the globe. From pre-industrial times to present, emissions from fossil fuel <br /> combustion and cement production have released 375 [345 to 405] GtC to the atmosphere (68%), <br /> while deforestation and other land use change are estimated to have released 180 [100 to 260] <br /> GtC (32%). Concentrations of CO2, CH4, and N20 now substantially exceed the highest <br /> concentrations recorded in ice cores during the past 800,000 years. Since pre-industrial times the <br /> estimated concentrations of CH4 have more than doubled (722ppb to 1,803ppb), while N20 <br /> concentrations have increased by a fifth (270ppb to 324ppb). <br /> Scientists believe that increases in atmospheric GHG concentrations results in an increase in the <br /> earth's average surface temperature, primarily by trapping and thus decreasing the amount of <br /> heat energy radiated by the Earth back into space. The phenomenon is commonly referred to as <br /> global warming. Global warming is expected in turn, to affect weather patterns, average sea <br /> level, ocean acidification, chemical reaction rates, and precipitation rates, all of which is <br /> collectively referred to as climate change. <br /> DOI-BLM-CO-N020-2017-0003 18 <br />