2017-05-23_GENERAL DOCUMENTS - M1977472

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Warming of the climate system is unequivocal, and since the 1950s, many of the observed changes are unprecedented over time spans of decades to millennia. The atmosphere and ocean have warmed,the amounts of snow and ice have diminished, and sea level has risen. Each of the last three decades has been successively warmer at the Earth's surface than any preceding decade since 1850. In the Northern Hemisphere, 1983-2012 was likely the warmest 30-year period of the last 1400 years (medium confidence). The globally averaged combined land and ocean surface temperature data as calculated by a linear trend, show warming of 0.85 [0.65 to 1.06] °C, over the period 1880 to 2012. In Colorado, the statewide annual average temperatures have increased by 2.0°F and 2.5°F over the past 30 and 50 years respectively. Warming trends have been observed over this period in most parts of the state, and show that daily minimum temperatures have warmed more than daily maximum temperatures. Additionally, temperature increases have occurred in all seasons. No long-term trends in average annual precipitation(30- 50 years) have been detected across Colorado, although since 2000 the state has experienced below-average annual precipitation and snow pack. The warming trends have contributed to an earlier shift in snowmelt and peak runoff timing in spring by approximately 1 to 4 weeks. Ocean warming has dominated the increase in energy stored in the climate system, accounting for more than 90% of the energy accumulated between 1971 and 2010 (high confidence). On a global scale, the ocean warming is largest near the surface, and the upper 75 m warmed by 0.11 [0.09 to 0.13] °C per decade over the period of 1971 to 2010. More than 60% of the net energy increase in the climate system is stored in the upper ocean (0-700 m), and about 30% is stored in the ocean below 700 m (40-year period from 1971 to 2010). The rate of sea level rise since the mid-19th century has been larger than the mean rate during the previous two millennia(high confidence). Over the period 1901 to 2010, global mean sea level rose by 0.19 [0.17 to 0.21] m. It is very likely that the mean rate of global averaged sea level rise was 1.7 [1.5 to 1.9] mm yr-1 between 1901 and 2010, 2.0 [1.7 to 2.3] mm yr-1 between 1971 and 2010, and 3.2 [2.8 to 3.6] mm yr-1 between 1993 and 2010, a trend that is increasing. The driver for the buildup in heat within the climate system is best described in terms of radiative forcing (RF). The term describes the energy balance that will occur (i.e. heating (+) or cooling (-)) in units of W m-2. The total anthropogenic RF for 2011 relative to 1750 was 2.29 [1.13 to 3.33] W m-2 (includes both heating and cooling parameter estimates). For well mixed GHG's the total positive forcing is estimated to be 2.83 [2.54 to 3.12] W m-2. The largest contribution to total radiative forcing since 1750 is caused by the increase in the atmospheric concentration of CO2. Emissions of CO2 alone caused an RF of 1.82 [f 0.19] W m-2 (64%), while CH4 caused an RF of 0.48 [f 0.05] W m-2 (17%). The data highlights methane's important role as a potent greenhouse gas, given its RF value in relation to its atmospheric loading trend, approximately 556 Tg yr-1 (64% anthropogenic, 36% natural) and relatively short atmospheric lifetime (12 years). N20 has the third largest forcing of the anthropogenic gases, at 0.17 [± 0.03] W m-2 (6%). Collectively the three GHG's of concern account for approximately 87% of the positive forcing within the climate system. DOI-BLM-CO-N020-2017-0003 19