Global Warming in The United States - Our Changing Planet

Since 1989, the U.S. Global Change Research Program has issued Our Changing Planet, an annual report summarizing "recent achievements, near term plans, and progress in implementing long term goals." (http://globalchange.gov/publications/our-changing-planet-ocp) The most recent report, for fiscal year 2010, was issued on October 28, 2009.

Measurement and modeling of climate systems have both improved dramatically in the last three decades, with measurements providing the hard data to calibrate the simulations, which in turn lead to improved understanding of the various systems and feedbacks and indicate areas where more and more detailed observations are needed. Recent developments in ensemble methods have improved understanding of and reduced uncertainty in hydrologic forcing by incoming radiation, particularly in areas with a complex topology. Multiple complementary model-validated proxy reconstructions indicate that recent warmth in the northern hemisphere is anomalous over at least the last 1300 years; using tree ring data, this conclusion can be extended somewhat less certainly to at least 1700 years. Improved measurement and analysis techniques have reconciled certain discrepancies between observed and projected trends in tropical surface and tropospheric temperatures: corrected buoy and satellite surface temperatures are slightly cooler and corrected satellite and radiosonde measurements of the tropical troposphere are slightly warmer.

Various forcing factors, including greenhouse gases, land cover change, volcanoes, air pollution and aerosols, and solar variability, have far ranging effects throughout the coupled ocean-atmosphere-land climate system. In the short term, impacts from ozone, black carbon, organic carbon, and sulfate on radiative forcing are predicted to nearly cancel, but long term projection of changing emissions patterns indicate that the warming impact of black carbon will outweigh the cooling impact of sulphates. By 2100, the projected global average increase to radiative forcing is approximately 1 W/m2.

Human activities influence climate and related systems through, among other mechanisms, land usage, water management, and earlier and more significant melting of snow cover due to greenhouse effect warming. In the southwestern United States, 60% of climate-related trends in river flow, winter air temperature, and snowpack between 1950 and 1999 were human induced. In this region, conversion of abandoned farmland to pine forests is projected to have a slight surface cooling effect, with evapotranspiration outweighing decreased albedo.